SOXHLET EXTRACTION

Soluble solids can be extracted from insoluble impurities by repeatedly leaching the impure solid using water or an organic solvent.
The soxhlet extractor is an efficient apparatus for such continuous extractions.

By leaching with refluxing solvent, the apparatus permits the extraction of delicate substances such as natural products which frequently require prolong extraction and are often heat sensitive.
The soxhlet extraction apparatus is in 3 distinct parts.
A heated round bottom flask containing extracting solvent
The soxhlet extractor itself which holds the material to be extracted in a thick porous paper thimble.

An efficient usually double surfaced reflux condenser
The heart of the apparatus is the extractor
This has a by-pass tube to allow vapor to reach the condenser, a sample chamber and a Siphon to return condensate from the sample chamber to the flask.

Material to be extracted us placed in a paper thimble which just fit in the wide part of the soxhlet glassware.
The thimble should be no more than 2/3 full.
Loosely packed glass or cotton wool placed on top of the solid serves to prevent any solid splashing out.

Then slide the prepared thimble into the soxhlet.
Its top must be at least 1cm above the top of the siphon tube
This prevents any solid being washed out into the siphon.
Next, fill around bottom flask of capacity 3 or 4 times that of the soxhlet 2/3 full to with the extracting solvent.

Securely clamp the flask resting either in a stem bath if flammable solvent is used or a heating mantle if a low flammability solvent is used.
Add a few anti-bumping granules
Then assemble the apparatus.
Remember that water will condense on apparatus heated over a steam bath so the joints must be greased to prevent water sipping inside the apparatus.

Connect the cold water supply to the bottom of the condenser and the overflow tube to waste.
Turn on the cooling water and heat the flask in this case in the heating mantle.
Adjust the rate of heating so that the solvent refluxes at a steady rate.
Vapor from the boiling solvent enters the wide tube on the right of the soxhlet and when it condenses drips into the paper thimble.
Since the sample chamber is sealed at its bottom end, the solvent passing through the thimble cannot reenter the flask until its level reaches the top of the siphon tube.
At this point, the siphon operates discharging the extract solution into the round bottom flask.

This cycle of events repeats every few minutes and it is continued for as long as it is necessary to complete the extraction.
Completion is judged by the disappearance of color from the fresh extract or if the extract is colorless simply by try and error.
If necessary, the extraction should be run for several hours.
Finally turn the heater off and allow the apparatus to cool.
Product can be recovered from solution by filtration and solvent removal.

SOLVENT EXTRACTION

When an organic compound has to be isolated from an aqueous mixture, solvent extraction using a separating funnel is often a quick and easy technique.

Non polar organic materials are usually soluble in organic solvents but not in water whilst
Non polar ionic materials are soluble in water and not usually in organic solvents.

This is the principle of like dissolves like
Separation can often be done by allowing the components of the mixture to distribute themselves between a water layer and a non miscible organic layer.

The piece of equipment used to mix up and separate phases is known as a separating funnel.
Funnels come in a variety of shapes and sizes but all have a stopper for the neck and a tap in the stem
The isolation of organic product from an aqueous reaction mixture containing unwanted ionic material is  a typical separation.
Having first ensure that the tap is closed, pour the mixture into a separating funnel of at least twice its volume.

Since the solvent used is likely to be flammable or toxic, the work should be carried out in a well ventilated fume cupboard.
The chosen solvent must be immiscible with water, have a low boiling point and preferably be of low toxicity
Diethyl ether is a popular choice.

When using such highly flammable solvents, ensure that there are no sources of ignition present.
The mixture should be extracted first with about one third of its volume of solvent then with two subsequent portions of about a quarter of its volume.
A slightly larger of volume is used for the first extraction because ether is not totally immiscible with water.
Less dense solvents like ether which floats on top of the aqueous layer, are handled in the following way:

Stopper the funnel and taking care to hold the stopper and tap in place, invert and gently shake the funnel.
Then release any built up pressure by briefly opening the tap.
Continue with progressively more vigorous shaking, always taking care to point the stem away from nearby colleagues when opening the tap.
After shaking for a few minutes, release the pressure.
Support the funnel in the ring and allow the layers to separate.
Once the separation is achieved, a series of transfers are needed to remove the upper solute rich organic layer and replace it with fresh extracting solvent.

Remove the stopper and run the lower aqueous layer into a suitable clean vessel such as a conical flask.
If the tap is opened without removing the stopper, irregular flow and some remixing can occur.
If this happens, close the tap and allow the layers to settle.
Then remove the stopper and open the tap once again.
Drainage should now be smoother.
Reduce the run off rate as the interface between the layers approaches the tap.

Close the tap just before the interface reaches it. Then swirl the funnel to dislodge any aqueous phase from the sides.
A soon as the aqueous layer has passed through, close the tap.
Pour the ether layer into a clean, dry conical flask.
Before continuing with the two subsequent extraction of the aqueous phase, securely stopper the flask.

Sequential extraction of the aqueous layer with two further small portions of solvent are recommended because this procedure will always achieve a more efficient separation than a single extraction with the same total volume of solvent.
Add the second and third ether layers to the flask containing the first extract.

Return the combined organic extracts to the separating funnel and wash with a similar volume of cold water to remove any water soluble impurities.
Since small amount of water are always left in the organic layer, it is common to wash this layer with saturated salt solution
With its high affinity for water, the brine removes dissolved water from the organic layer and so act as a preliminary drying agent.
Combine the aqueous washings with the aqueous layer and label the flask.

Do not discard this until the final product has been recovered successfully.
When the extracting solvent is more dense and form the lower layer, the transfer procedure is not necessary
The lower solute rich layer is simply run off and fresh portion of solvent added to the separating funnel to further extract the less dense phase.

Either way, dry the combined organic extract by adding a desiccant such as anhydrous magnesium sulfate.
The first few grams of the desiccant may form dense hydrated lumps which stick to the bottom of the flask.
Add further desiccant until free powder is suspended when the flask is swirled and settles only slowly to leave a clear solution.
Then stopper the flask and periodically agitate it over a period of 5 to 10mins to ensure the extract is thoroughly dried.
Remove the desiccant by filtering the mixture through a funnel lightly plugged with cotton wool.

Or under suction through a filter paper in a hush funnel.
Finally strip off the solvent in a rotary evaporator and purify the residue by recrystalisation for a solid
or distillation for a liquid.
Sometimes agitation of the two phases will produce an emulsion.
Filtering the mixture will often break the emulsion but there are no hard and fast rules for these situations. It a case for experimentation
The addition of cold saturated Brine is frequently successful in breaking emulsions.

This is because emulsion often form when the solute dissolved in the immiscible liquid has made their densities very similar or where a surfactant is present
The Brine increases the density and ionic nature of the aqueous phase.
This makes the density of the two phases less similar and helps to reduce the emulsifying effect of surfactants.
Another strategy is to add more solvent thereby decreasing the density of the organic phase by reducing its solute concentration.

USING CONDUCTIVITY CELLS

Measuring the conductivity of a solution provides information about the degree of ionization of solute present in that solution.
The usual solvent is water but other polar solvent such as acetyl nitrile and dimethyl  sulfurside can be used.

A common cell for conductivity measurement is the Dipping Electrode Cell.
Its platinum electrodes are plated electrolyticaly with platinum black.
This coating is delicate. So handle the cell gently and never touch the platinum surfaces.

No two dipping electrodes are physically identical. So begin by calibrating the cell with the solution of known conductivity e.g 0.1M Sodium Chloride.
Connect the cell to the conductance meter and switch it on.
Thoroughly rinse the dipping electrode with the calibrating solution
Discard the solution and replace with the fresh sample of the same calibration solution.

Ensure that there are sufficient solution to cover the electrodes and that the electrodes are clear of the stirrer.
Then switch on the stirrer.
The stirring should give just sufficient agitation to remove any air bubbles from the electrode surfaces.

The temperature of the solution must be measured because conductivity changes with temperature and the calibration solution’s conductivity will be compared with reference data.

Next, adjust the meter controls to find the null point.
Choose a scale range that gives a null point with the scale reading that is greater than 1.
If there is no reading, check that all the leads have been properly connected.

If still no reading is obtained, consult a member of staff.
Leave the system for about 2mins to equilibrate.
Then bring the needle to the null position and note the scale reading for the calibration solution.
Use this value to calculate the cell constant as described in the laboratory notes.

Once the cell constant has been determined, the apparatus can be used to measure the conductivities of other solutions.
Before each measurement, remember to rinse the cell with the new sample solution before measuring its conductivity.

Always remove the cell from solution as soon as possible after each reading and wash it with distilled water.
This prevents deteoration of the platinum black surfaces.
After use, store the cell in distilled water in its container.

USING ELECTROCHEMICAL CELLS TO DETERMINE THERMODYNAMIC PARAMETERS

Commercial common batteries are example of electrochemical cells being so compact and sealed they provide a convenient and safe means of examining the thermodynamic parameters of the reactions which take place within them.

Place the cell in a spring loaded holder and make the connections to the cell.

Immerse the cell in a large tube partially filled with paraffin oil containing a thermometer.
Switch on the digital voltmeter connected to the cell.
Warm the tube gently with the Bunsen burner until the temperature is above 50deg Celsius.

Remove the Bunsen and take the DVM reading just as the temperature falls to 50deg Celsius.
As cooling continues, take further readings until the temperature has dropped to about 20deg Celsius.
The reading should then be repeated with increasing temperature over the same range.
This provides a check that the cell is in equilibrium.

Plot a graph of the meter readings against the temperature.
Entropy gives energy and entropy changes can be obtained using the standard equations given in the lab script.

USING AN AUTOMATIC TITRATOR

Automatic titrators work to high analytical standards and are particularly useful when a large number of similar titrations are to be done.
They can carry out a variety of types of titration such as

Acid-Base Titration

Oxidation-Reduction Titration

Photometric Titration

Conductometric Titration

Each type of titration has its own dedicated burette.
A titration vessel containing automatic detection system commonly an ion specific combination electrode and titration parameters which are stored under discrete method numbers in the instrument.

Begin by
Choosing the relevant titrant, fitting the automatic burette and
keying in the appropriate method number for the titration.
Ensure that correct electrode is fitted to the titration.
Always wash the electrode with distilled water before use and between measurements.
Fit a beaker containing a pipetted aliquot of the acid sample and sufficient distilled water to ensure that the tip of the electrode is completely submerged.
Press the run button to begin the titration process
And then set the detailed titration parameters e.g. Identity of sample, sample weight or sample volume.
Press the run button again to activate the stirrer and carry out the titration.
The progress of the titration is shown on the LED display.
During the titration, the automatic burette delivers metered volumes of titrant.
These volume and the corresponding electrode readings are stored in the memory ready for access at the end of the titration.
When the titration is complete, the printer can plot out the results in a variety of formats.
As a full set of millivolt or PH data points with the corresponding titrant volumes, a table of result together with the graph or as here, simply a graph of PH versus titrant volume.
The end point corresponds to the mid-point of the steep section where the PH changes most rapidly.

Note that this machine plots the volume in milliliters which are equivalent to cubic centimeters.
Here, the machine had plotted the result of a strong acid–strong bas titration as millivolt versus volume.
Again, the end point is at the mid-point of the steepest section of the curve.
A plot of the first derivative of such millivolt or PH curves can also be produced.

In such plot, the end point is much more obvious as the point where the slope of the curve changes direction.
Such plots are particularly helpful when it is difficult to determine the mid-point of the steep section such as in the titration of a weak acid with a weak base or vice versa.
At the end of any titration, remove the sample beaker and rinse the stirrer, burette tip and electrode.

Note that electrodes must not be allowed to dry out. So immerse them in reference electrolyte when not in use.

CONDUCTIOMETRIC TITRATION

Conductiometric titrations are particularly important where visual and potentiometric methods fail such as when hydrolysis occurs at the end point or where a moderately soluble precipitate forms.
In addition, comparable accuracy can be obtained for both dilute and concentrated solutions.
Start by suspending the conductivity probe in a beaker containing a large measured volume of distilled water equipped with the magnetic stirrer.
The large volume ensures the probe can be submerged and kept clear of the stirrer bath
Also, it will minimize the change in conductivity due to dilution when the titrant is added.
In this demonstration, the unknown sample is a strong acid and it could be titrated with the standard 0.1M sodium hydroxide as the titrant.
Holding the pipette vertically, use the pipette filler to draw the sample solution into the pipette until the meniscus is just above the graduation.
Remove the pipette from the solution, and allow the meniscus to fall to the graduation.
Use the edge of the beaker to remove any drop from the end of the pipette and transfer the sample to the titration beaker.
Allow the pipette to drain for 10sec.
Then touch the tip of the pipette in the solution to ensure the calibrated volume has been delivered.
In titrations, only changes in the conductivity of the solution are followed.
So it is not necessary to calibrate the meter or monitor the temperature.
Switch on and find the appropriate scale range.
Then determine the conductivity reading.
The meter reading should be near the middle of the scale.
If the initial is near the bottom of the scale, a scale change might be necessary during a titration and this is undesirable
In such a case, increase the volume of the sample added so that the initial meter reading is near the middle of the scale.
Clamp a clean burette in the stand, and using a funnel, fill it with the titrant.
 In this case, 0.1M sodium hydroxide.
Fill the burette to a centimeter or so above the zero mark.
Then run titrant into a waste beaker until the meniscus reaches the zero mark or a lower graduation that can be viewed easily.
Sometimes, lighting effect can make it difficult to judge the position of the meniscus.
The use of a black and white card can be helpful as it makes the meniscus completely dark and easy to read.
Whether such an aid is used or not, when taking a reading, always have your eye level with the meniscus.
If the meniscus lies between calibration marks, estimate its position, here it is 4.61
Remove any drop from the tip of the burette by touching it against the waste beaker.
And position the filled burette over the beaker of sample solution.
Note the initial burette reading in your lab book and check and record the initial conductivity reading.
Add 1cubic cm of titrant and allow the system to stabilize and note the new conductivity and burette readings in your lab book.
Continue to add 1cubic centimeter aliquot of titrant.
A point will be reached where the conductivity stops decreasing.
Then continue the additions until a volume of titrant added at that point is approximately doubled.
At the end of the titration, remove the Dipping Electrode, wash it with distilled water and return it to its storage container.
Plot a graph of the conductivity readings against the volume of titrant added.
The graph should show a distinct change in gradient of the end point as in this graph for a strong acid titrated with a strong base.
For maximum accuracy, the data can be corrected to allow for the dilution effect caused by the addition of titrant.
If the graph is curved, in the region of the end point, straight lines are drawn through the point as shown.
The point of intersection of these straight lines is taken as the end point.

ELECTROCHEMICAL METHODS FOR DETERMINING SOLUBILITY PRODUCTS

ELECTROCHEMICAL METHODS FOR DETERMINING SOLUBILITY PRODUCTS

 Measuring electrode potentials is a good method for determining solubility products because the measurement do not disturb the equilibria involved
This experiment describes the procedure for measuring the solubility products of some silver salts
Begin by preparing a saturated solution of silver chloride by adding 1 to 2 drops of 0.1m silver nitrate solution to approx 100cubic cm of 0.01M solution of potassium chloride.
To form a reference half cell; place a calomel electrode into a beaker containing saturated potassium chloride solution ensuring that the fret is completely immersed in the solution
Place the two beakers side by side and connect them using an ammonium nitrate salt bridge.
Immerse a clean sliver electrode in the solution to form the silver half cell
The two electrodes are connected to a digital voltmeter.
Gently agitate the solution.
If the electrode is fragile, use a magnetic stirrer.
When the reading on the digital voltmeter steadies, note the reading.
If the sign is negative, simply change over the terminals
But note the polarity of the cell, i.e. which electrode is connected to the positive terminal when entering the result in your lab book
Repeat the experiment adding 1 drop of 0.1m silver nitrate solution to 0.02, 0.05, 0.1 and 0.2M solutions of potassium chloride in the silver electrode beaker.
Remember to wash and dry the electrode and bridge between measurements and always to put the same end of the salt bridge in the silver solutions.
Carry out analytical experiments for other silver salts by replacing the potassium chloride in the silver electrode beaker by solutions of known concentrations of potassium bromide, iodide, and chromate.
Calculate the silver electrode potentials and obtain the solubility products as described in the lab script.

STANDARD ELECTRODE POTENTIALS DETERMINATION

DETERMINATION OF STANDARD ELECTRODE POTENTIALS

The potential of an electrode is obtained by measuring the potential difference across a cell comprising that electrode and a reference electrode of known potential.
The electrode whose potential is to be measured here is a Silver electrode.

It is connected via a digital voltmeter to a saturated calomel reference electrode immersed in a saturated of solution of potassium chloride.
A salt bridge is used to connect the 2 solutions
The silver electrode comprises a silver rod in an appropriate solution
It is important for the electrode to be in good condition and free from surface contamination
A good way to ensure this is to immerse the silver rod briefly in dilute nitric acid.
Rinse with distilled water
Then dry gently with the tissue and place it in a 100 cubic cm beaker.
To form the silver half cell, pour some 0.001 molar silver nitrate solutions into a beaker.

It is important to add enough solution to completely cover the metal part of the electrode.
To form the reference half cell, pour saturated potassium chloride solution into a beaker.
Immerse the reference electrode ensuring the freight is completely covered by the solution
Place the 2 electrode beakers close together and lower the salt bridge into them.

Typically the salt bridge consist of a solution of ammonium nitrate in an agar gel.
Salt bridges containing potassium chloride must be avoided in this experiment because the chloride ions will react with the silver ions in silver nitrate to produce a precipitate of silver chloride.
Digital voltmeters known as DVMs Aare well suited for these measurements because they draw very little current.

This is important because the electrode potential is an equilibrium value and drawing current disturbs the equilibrium
With the meter on, switch the dial to V for volts and set the DVM to read DC.

After setting up the DVM connect the electrodes to the V and Com terminals of the DVM.
Then switch on again.

Note that it is possible to connect the electrode the wrong way round.
If this happen, a negative sign appears in the voltage display
This is nothing to worry about. The electrodes may be changed over.
It is necessary however to note which is the positive terminal when tabulating the results.

A problem which sometimes occur is for the potential difference of the cells, drifts slowly with time
Gentle stirring will usually overcome this problem giving a reasonably steady reading but take great care if the electrode is fragile.
If the drift persists, consult a member of staff.
Having measured the voltage of the cell using the 0.001M silver nitrate solution, repeat the measurement using solutions of different concentrations.

And tabulate the result in your lab book.
Don’t forget to rinse and dry the electrodes and the slat bridge before each measurement
And be sure to replace the salt ridge with the same end of the bridge in the silver solutions.

Plot a graph of the meter readings against the log of the silver nitrate concentrations.
The intercept on the vertical axis on the slope of the graph allow the calculation of the standard electrode potential of the silver half cell as described in the lab script.

USING GALVANIC CELLS

A galvanic cell consist of two half cells of different potentials.
A digital voltmeter measures the potential difference between them.
A salt-bridge sometimes completes the circuit.
One half cell contains a reference electrode and otherwise closed unit in the electrical contact with the other half cell
Reference electrodes maintain constant known potentials.
An example is the saturated calomel electrode
This apparently sealed probe has a glass fretted space which provides electrical contact with the surrounding liquid.
The other half cell which contains the indicator electrode has a potential which changes with the properties of the solution it dips into.
Examples of commonly used indicator electrodes are
The Silver Electrode
The Platinum Electrode
The Glass Electrode whose potential varies with the concentration of Hydrogen Ions and so is used in PH measurement
And there is the other
Ion Selective Electrode whose potential depend on the concentration of Ions like fluoride and Nitrate
Two half cells can be combined into a single probe as in the measurement of Ph
Such probes are usually more robust than single electrodes
It is essential that electrodes are in good condition and free from surface contamination.
If you have any doubt about this, ask a member of staff.
Handle electrode carefully. They are often expensive and easily broken.
Take care to mount fragile electrode well cleared of magnetic stirrer baths.
Electrodes are very sensitive. So when taking measurement on a series of samples, It is important to rinse the electrode and then the bridge used thoroughly with distilled water.
Then dry them before taking the next reading.
Alternatively, they may be rinsed with some of the next solution to be measured before taking readings using a fresh sample of that solution.
At the end of the set of measurements, wash the electrodes with distilled water and return them to their storage containers.
Electrodes left lying around can become contaminated or dry out and become unusable.
When using a digital voltmeter, the correct scale of the meter must be chosen and the meter must be calibrated.
So for Ph measurements, the meter’s PH scale is selected.
And the scale is calibrated using standard buffer solutions of accurately known ph.
The PH of any sample solution can then be read.
Salt bridges contain metal salts in an agar gel
They come pre-pared or else can be made as required as illustrated by the bridge shown here.
It is important the salt in the bridge does not react with the ions in the cells.
For example, potassium chloride in a salt bridge will react with silver nitrate in a cell solution.
If this happens, both the bridge and the solution are ruined.
At the end of an experiment, rinse the end of the slat bridge with distilled water; remove the excess water with tissues
And store the salt bridge in a storage container such as desiccators but without desiccant.

STEAM DISTILLATION

STEAM DISTILLATION

Steam Distillation is a method of distilling a compound at a temperature below its normal boiling point.
The underlined principle being that when a mixture of compound is distilled, it boils at a temperature at which the sum of their vapor pressures is equal to atmospheric pressure.
Usually the process is used to distill an organic liquid or low melting solid that is immiscible with water.

It is particularly used when a volatile product has to be separated from a mixture which is mainly in -volatile
Steam can be supplied from the steam generator or a pipe laboratory supply, or water can be added to the distillation flask.
Either way, it’s important that the distillation flask is heated so that water doesn’t accumulate in it.

In the simple water addition method, a two necked flask containing mixture and a few anti-bumping granules is fitted with the dropping funnel containing water and a splash head.
All forms of steam distillation require an efficient double-surfaced condenser since large amount of steam have to be condensed.
The flow of water need to be faster than usual, so the tubing must be securely attached.

A large receiver should be used. Usually a conical flask and spare receiver should be at hand as the volume of distillate is often very large.
Ensure that the distillation flask is no more than half full at the start of the distillation and heat the crude compound water mixture to boiling before adding additional water.
When an immiscible substance is being steam distilled, the distillate may be cloudy and low melting solid will separate out as the distillate cools.
From time to time, add more water to keep the distillation flask half full.

When a low melting solid is being steam distilled, it may begin to collect in the condenser and could block it if allowed to continue.
In such cases, periodically clear the condenser by turning off the water supply and detach the tubing from the tap to allow the condenser to empty.

As the condenser heats up, the solid will melt and flow into the receiver.
Once the condenser is cleared, reconnect the tubing and turn on the water supply again.
The steam distillation should be continued until the cooled distillate shows no further traces of the immiscible organic compound.
Solid is recovered from the distillate by simple filtration and then dried to remove any remaining water
Immiscible liquids are separated from the water in a separating funnel then dried over a drying agent.

When steam is supplied from a generator or a pipe laboratory supply, the dropping funnel is replaced by steam inlet pipe.
Before the flask is charged, adjust it so it is long enough to reach the bottom of the distillation flask.
The distillation procedure is otherwise the same as in the water addition method.
When the distillation is finished, dismantle the apparatus while it is still warm.
This will prevent residues in the flask from hardening on its surface and so make cleaning easier.

FRACTIONAL DISTILLATION

Simple distillation can separate compounds which boil at temperature more than about 500C apart.
But from 500C apart down to the distillation limit of around 50C, a fractionating column has to be used.
In a fractionating column, a descending stream of condensate mixes with an ascending stream of hot vapour.

The mixing of gas and liquid and the temperature drop up the column cause the vapour to become more concentrated with the most volatile component moving towards the top of the column while the less volatile components drain down in the liquid returning to the flask.
Here the thorough mixing is achieved with specially designed bubble caps.

Much ingenuity is being employed in designing fractionating column to provide surfaces that give good mixing between vapor and liquid.
One of the simplest is a straight column packed with rings or beads to give a large surface area for gas-liquid exchange.
A fractionating column works best when the liquid it contains is simply heated by the ascending vapor with no gains or losses of heat to the surroundings.

Thus a fractionating column is usually insulated.
In this case with the vacuum jacket
Such a fractionating column is capable of separating substances boiling more that 200C apart.
The best heat source for fractional distillation is an oil bath mounted on a hot plate.
And the column is located between the distilling flask and the distillation head.

As with any distillation, the first job is to charge the distillation flask.
Add a few anti-bumping granules, then the liquid to be separated.
Fit the fractionating column and check that it is vertical.
Then fit a distillation head on top of the column
The remaining assembly is the same as simple distillation
The only difference is the need for blocks, extended lab jacks and the high retort stand to accommodate the height of the fractionation column.

A tube from the take off band leaves any traces of very volatile components to an extractor port.
Conical flasks which are easy to change quickly are used to collect the distillate fractions.
The oil bath is fitted with a thermometer and mounted on a lab jack so that it can be raised or lowered to give fine control of the rate of distillation.

The initial stage of a fractional distillation is to achieve equilibrium between vapor and condensate in the column and the first step is to ensure that the vapor reaches the top of the column.
Then lower the oil bath to keep the head temperature at that point for about 5mins.
When this is being done, equilibrium between valor and liquid is being set up, raise the oil bath and distill the material slowly.
If vapor is distilled too quickly, the equilibrium set up in the column will not be maintained and so efficient separation will not be achieved.
Ideally, the distillation should be around such rate that every ten drop of condensate that fall back into the column  and drop falls into the receiver.

This is known as the reflux ratio.
When a component has been distilled off, the distillation temperature will change. Usually it rises as the next component is distilled.
 Very clear separation of the components is such that no vapor comes over for a time, then it may fall before rising again to the boiling temperature of the second component.

 Change the flask as soon as the temperature changes.
When it is stabilized at a new level, change the flask again and collect a higher boiling component.
The fractionating column can be cleaned by distilling over a low boiling compound.
This will displace any higher boiling materials and evaporate off when the apparatus is dismantled.

DISTILLATION AT REDUCED PRESSURE

High boiling liquids and many liquids which have a tendency to decompose near their boiling temperatures are often purified by distillation under reduced pressure.
Since lowering the pressure dramatically reduces the temperature at which a liquid will distill.
Distillation under reduced pressure always carries a slight risk of the apparatus imploding.

For this reason, such distillation should be carried out in a fume cupboard or behind a toughened safety glass screen.
Always examine flasks very carefully for star cracks before using them under reduced pressure.
One of the significant changes from simple distillation is the need for the 2 neck claisen head in place of the distillation head.
As with simple distillation, insert a thermometer in a neck nearest the outlet.
And attached a water cooled condenser to the outlet joint.
Insert a capillary bleed into the other neck.
This may have either a rigid or a screw cap quick fit joint. But the later is easier to adjust to the correct neck. Do this before assembling the apparatus.

Lightly grease all the joints to prevent air leaking into the apparatus.
Attach a plastic clip to secure the joint between the claisen head and the condenser
There is no need to clip the thermometer or the capillary bleed.
Since the major cause of the decomposition of hot liquids is oxidation, it’s usual to draw oxygen free Nitrogen through the bleed.
The simplest way to do this is to use a Nitrogen filled balloon.
Attach this to the end of the bleed.

The fine bore of the capillary will prevent a rapid escape of the gas even under reduced pressure.
Use a multi-flask receiver adaptor to allow the receiving flask to be changed without letting air into the apparatus.
Carefully grease the upper part of the condenser cone so that the joint will rotate even when there is reduced pressure in the system.
A plastic clip securing this joint will still allow it to rotate easily.
The receiving flask should be held in place by clips and only very lightly greased.

For many applications, a water pump gives an adequate reduction in pressure such as down to 20-25 Hgmm.
If a lower pressure is required, use a rotary oil pump which easily gives pressures down to few mm or less.
When using an oil pump, always insert a trap cooled with dry iced acetone or a similar coolant between the pump and the distillation apparatus.

This is to prevent pump damage caused by solvent filling the pump lubrication oil.
Attach suitably thick walled tubing from the trap to the outlet on the receiver manifold.
In this case, the apparatus with reduced pressure distillation has been assembled in a fume cupboard to give the necessary protection in case of implosion.
Heating is best supplied by a heated oil bath mounted on a lab jack.
At the start, make sure the liquid in the bath is leveled with that in the flask.

Suspend the thermometer in the oil to monitor the bath temperature.
Position the safety screen to provide adequate protection but leave a small space for access to the apparatus.
With the pump on, close the vent to the suck-back trap.
Then open the Nitrogen bleed. Bubble should appear immediately.
Any traces of low boiling components in the liquid will rapidly be drawn off into the water pump of the cold trap.
As the bath temperature rises, distillation of the first few drops of liquid begins.

Collect distillate in the first receiver until the distillation temperature becomes steady.
Then rotate the receivers to collect the main fraction in the larger flask located on the central arm of the manifold.
Collect the third fraction in the remaining flask if the temperature changes again while there still liquid in the distillation flask.
When the level of liquid in the distillation flaks is near the bottom of the bleed, or a foaming is observed in the flask, lower the oil bath.
Continue to draw Nitrogen through the apparatus for 5 -10mins while it cools.
Then release the vacuum by letting air into the system through the vent tap on the trap.
Then switch off the pump.
Finally, unclip and stopper the flask and if necessary, weigh them and record their weights.
Dismantle the apparatus for cleaning before it cools completely.

DISTILLATION AT ATMOSPHERIC TEMPERATURE

Simple distillation at atmospheric pressure may be used to purify liquid that boils below about 2000C without decomposition.
To begin with, clamp the flask and fit it with the distillation head.
If the boiling temperature isn’t known, use water cooled condenser – A Liebig condenser.

It helps to secure the joints with a clip.
Cradle the condenser on the fixed jaw of the clamp
Close the upper jaw to hold it firmly but not too tightly. It should still be possible to rotate the condenser.
Attach a tip take off band and secure it with a clip.
Three receiving flasks are usually needed for distillation.
The largest should be big enough to contain at least three quarters of the liquid to be distilled.

In a quantitative distillation, all three flasks with their stoppers must be labeled and weighed before collecting any distillate in them.
Attach the 1st receiving flask supporting it with a cork ring on a lab jack.

The cork ring should be oversized so that it will cradle the flask should it fall from the take off end.
Alternatively, clamp the flask (not the take off end) using a further clamp on a stand.
The early distillate may be very volatile and flammable, so attach a length of tubing to lead any uncondensed vapor down the zinc with running water or into an extractor port.
Attach the rubber tubing from a lower side arm of the condenser to the water tap.
Slide it up until is firmly fixed.
Water should always flow up the condenser jacket.
Keep it steady but not too powerful water flowing and check it from time to time.

It is best to wire the tubing unto the condenser.
If the liquid is known to have a high boiling temperature, an air condenser can be used from the start.
When carrying out distillation at atmospheric pressure, a few anti-bumping granules should be added to ensure smooth boiling.
Use them only once and just a few at a time.
They should be added to the flask before the liquid. Don’t try to add them through an already wetted funnel they may stick to the sides.
The stem of the funnel used to introduce the liquid into the flask, must extend below the side arm or crude liquid may accidently get into the condenser.

The flask should be filled not more than two third full from the start of the distillation.
With care, fix a quick fit thermometer into the distillation head to monitor the distillation temperature.
Remember they are expensive and fragile.
The usual source of heating is a water or oil bath set on a hot plate or stirrer hotplate.

The foil prevents any spillage burning on the hotplate.
It’s wise to have the bath on a lab jack so that the heat source can be raised or lowered quickly.
The level of the oil in the bath should be positioned just about the level of the liquid in the flask.
Switch on the stirrer hotplate, adjust the stirring rate.
And at first set the heating rate to maximum until the liquid starts to boil.
Suspend a thermometer in the oil to monitor the temperature of the heating bath.
At the first sign of boiling, reduce the heat to certain point that a steady boiling is just maintained.

The temperature usually begin to rise rapidly but soon settles down to a steady value as vapor begins to condensed about the thermometer bulb and drifts from the outflow of the distillation end.
Record this initial temperature, and adjust the bath temperature to between 30 – and 500C above it.
Distillate should drip into the receiver at about 1 drop a second. The first few drops may be cloudy,
When the temperature has remain steady for half a minute, note it , then change the receiver and collect the bulk of the liquid in the second flask.

If the rate of distillation becomes too high, the heating can be quickly reduced by lowering the oil bath.
Generally the bath should be lowered as the liquid levels inside the flask falls during distillation so avoiding the  danger of the flask overheating and causing returning condensate to decompose,
When most of the liquid is distilled, the temperature may begin to fall slightly, until the vapor of higher boiling reaches the thermometer, at this point, note the temperature and change the receiver again.
After this had been collected, a little more liquid may distill over giving 3 fractions in all.

At the end of the distillation lower the lab jack to remove the heat source, don’t heat the flask to dryness or even nearly so, it could be dangerous, for example the residue may be explosive or decompose to give toxic fumes.
Finally, let the apparatus get cold before dismantled it, and clean it as soon as possible.

PREPARATION OF GRIGNARD REAGENT

During the preparation of a Grignard reagent, it is important to exclude moisture.
So the apparatus consisting of a tapered flask, Magnetic Stirrer bar and a Liebig condenser should be assembled while it is still warm after drying in an oven at about 1200C.
The top of the condenser is sealed with a septum cap and fitted with a hypodermic needle attached to a drying tube.

The condenser is connected to the cold water supply.
Before the apparatus assembled, weigh out about 30mg of magnesium turnings and put them into the tapered flask.
Then add a small crystal of iodine.a
Transfer 100micro lit of Bromo Benzene at a 156mg to a small specimen tube and dissolve it in 1 cubic cm of diethyl ether that has been dried over sodium wire.
Cap the tube.
Take out about 0.3 cubic cm of the Bromo Benzene solution in hypodermic syringe fitted with a 15cm needle.
Insert the needle through the septum cap as far as it will go.
Inject the solution onto the magnesium.
Then start the stirrer.
As the reaction begins, the initially brown solution becomes colorless and the ether begins to boil.
If it is slow to start, it can be heated with a hot air blower.
Once the reaction starts, add the rest of the Bromo-Benzene solution drop-wise.

When the addition is complete, remove the syringe, raise the apparatus, then put a  sand  bath  unto the hot plate, lower the flask into the sand and begin heating the bath up to about 600C.
Stir and heat the reaction mixture on the reflux for 30mins.
Measure out 100 microlit of propyol phenol, add to it 0.5 cubic cm of dry di-ethyl ether
Haven taken away the sand bath, and allow the reaction mixture to cool,
Insert the hypodermic syringe containing the propyol phenol solution to the septum cap and add it clockwise.
There is an exothermic reaction.

When all pro solution has been added, replace the sand bath and heat the stirred reaction mixture under reflux for a further 10mins.
Then remove the apparatus from the sand bath to allow the reaction mixture to cool.
When it has cooled, remove the flask from the condenser.
Transfer the reaction mixture into a small specimen tube containing cold dilute sulphuric acid.

 Rinse the reaction vessel with a further 0.5 cubic cm of Di-ethyl ether and add the rinsing to the tube.
Mix the two layers repeatedly until both are clear.
Allow the layers to separate.
Then pipette out the water layer (the bottom layer) into another container.

Dry the remaining Di-ethyl ether solution of the product with anhydrous magnesium sulphate.
Filter the Di-ethyl ether solution through a cotton wool plug into a clean dry tube.
Rinse the drying agent and the filter with a little more ether.
Expel the last traces of ether from the filter by pressure from a rubber teeth.
Add an anti-bumping granule and carefully boil off the Di-ethyl ether.
Remove the last traces of solvent and pushing the tube down into the sand.
The Residue should solidify on cooling and can be purified by re-crystallization.

GOS CHROMATIGRAPHY

Gas Chromatography is an instrumental method for separating and analyzing sub microgram amount  of volatile liquid and volatile solids and gases.
The separation takes place as the sample vapor passes through a coil tube and a column, which is housed in a temperature controlled oven.
There are two types of column, capillary column and packed columns.
Packed columns are stainless steel or glass tubes around half a centimeter internal diameter and 1-2m long.

The column is packed with a stationary phase with either a finely divided solid support on which a high boiling inert liquid is being absorbed or just a finely divided solid such as silica or carbon.
Capillary columns are very fine silica tubes between 10-15m long, then about a half a millimeter internal diameter, here the high boiling liquid is chemically bonded on the inside wall of the capillary.
These columns are capable of much better resolution than packed columns.

The sample vapor is transported through the column by a mobile phase, an inert carrier gas such as Nitrogen or Helium.
To start, check that the instrument is turned on. It’s common in many laboratory to leave these instrument permanently switched on.
Check that the carrier gas flow rate is as specified in the instruction sheet, typically 1-2cubic centimeter per minute in the capillary column or 30-60 cubic centimeters per minute in a 1-2meter packed column.

The sample movement vaporized in a pre-heated in the injection pot prior to entry of the column, so set the appropriate injector temperature, then set the column working temperature.
Be careful not to allow the oven temperature not to exceed the upper temperature limit of the column, otherwise the stationary phase may be stripped through the column.

Now leave the instrument to stabilized, this normally takes a few minute, modern instruments displace the word ready at this point.
Since gas chromatography is a very sensitive technique, the sample will usually need to be diluted, make a solution in an inert volatile solvent such as diethyl ether which will elute through the column quicker than the sample.

Typically a sample concentration needed will be about 1%.
The Gas Chromatography is capable of analyzing 1part per million or less.
Wash up the hypodermic syringe with the sample solution and then drop up a measured volume, typically 1-3microliters.
Then inject this through the self sealing septum injection pot taking care not to bend the needle.

Most modern instruments automatically records the time of the injection in this case is the origin where the trace started to draw, otherwise note the injection point.
Gas samples are best introduced into the instrument using a gas syringe, or by means of a fixed volume gas loop, typically at 1cubic centimeter capacity.

The loop is incorporated into pipe or the edge of the column and is filled using a syringe or by drawing the sample gas through it.
Opening the loops isolating valve allow the carrier gas to stripped the gas sample into the column, as the separated component emerge from the column they pass into the detector and the resulting  electrical signal are displayed on the VDU or a moving chart.
Each separated component should give rise to a single peak, a variety of detectors are available Choice depending on the nature of the sample the analyte.

The flame ionization detector is suited to combustible analytes such as Hydrocarbons or alcohol, Nitrogen or Helium is used as the carrier gas.
The electron captured detector is suited to halogenated compounds; the carrier gases used are Nitrogen, Helium or Argon.
The most sophisticated detector is the mass spectrometer.
In a GCMS instrument the separated component pass through the column, at a heated transfer line into a mass spectropheter.

This is the only detector capable of directly determining the identity of the components. Other detectors can only do so by reference to pure samples of the suspected compounds.
The time elapsed between the sample injection and the appearance of peak maximal is called retention times.
Modern instrument will automatically displayed the retention times corresponding to each peak maximum.

The correlation of the component retention time with that of the separately injecting pure compound could be taken as strong evidence of the component’s identity.
But co-injection of the analyte and standard is a more reliable procedure; add a known standard compound solution of the unknown sample and inject the mixture unto the column, if the standard compound is present in the unknown sample then one of the peaks in the case and second will be relatively higher than in the original chromatogram. If not an addition peak will occur.

The area under each peak is proportional to the amount of the compound caught that peak.
But before this could be used for quantitative analysis it is necessary to calibrate the instrument to allow a varying detector response to different compounds and different samples modes.

Commonly, the correction factor are stored in the computerized data handling system of the instrument and used automatically when the sample data is printed out.
An unknown concentration could then be found by injecting the sample solution and determining the peak area from the trace and hence percentage concentration.

ION EXCHANGE CHROMATOGRAPHY

Ion exchange chromatography can be used to measure the concentration of ions usually in aqueous solutions.
In a case of cations, a cationic resin is used as the column
The resin is a polymer with sulphanate end-groups represented here as a lipsis which rapidly exchange cations.

For instance sodium ions might replace hydrogen ions.
To prepare the resin for use, suspend it in deionised water and stir well to remove air bubbles.

New dry resin needs to be soaked for about 5mins and any fine powder decanted from the surface of the water.
The resin that has been used already will be damped and does not need soaking.
The glass columns that are used for chromatography often have a wider section at the top to act as a reservoir.
There is a tap at the base of the column and in this case, there is a glass fret above it.

The fret will prevent ion exchange resin blocking the tap and such column needs no preparation.
If the column does not have a fret, first add about 5 cubic cm of deionised water to the column.
Then take a piece of glass wool and using a glass rod, push it to the bottom of the column.

Clog the glass wool to release any air bubbles and pack it down the formal plug which will prevent resin entering the tap.
Put the resin slurry carefully into the column.
Allow the resin to settle and then drain off excess water from the bottom of the column but don’t let the top of the column become dried out.
Leave enough room at the top of the column to add the sample to be analyzed.
Close the tap when the water level at the top of the column is just above the resin.

If any air bubble becomes trapped, it must be released by stirring the column with a glass rod
This is to ensure that the solution uniform and maximum contact with the resin.
When old resin is reused, it will contain a variety of cations M+ bound to the sulphanate groups.
Such resin must be regenerated by treating it with concentrated acid so to drive the equilibrium to the right and leave the resin in the acid form.

To do this, carefully add about 25cubic cm of 6M Hydrochloric acid to the column, disturbing the top of the column as little as possible.
Partially open the tap and let the acid slowly run through the column.
This will result in all the cation being replaced by hydrogen ions.
When the acid level as come down to the top of the resin, turn off the tap and add deionised water to the top of the column.
Open the tap and run out the water. This will remove excess acid from the column.

It requires several refills to wash all the excess acid from the column.
From time to time, sample the washing and test them with an indicator such as screened Methyl Orange.
The reddish color indicates that the test portion is acid and that further washing is needed.
Continue washing the column until the test portion shows that the effluent in neutral.

With the water level just above the top the resin, withdraw 25cubic cm of the sample using a pipette.
And add this to the top of the column taking care to disturb the column as little as possible.
With a large conical flask in place below the column, partially open the tap so the liquid slowly percolates down the column.
When the liquid level reaches the top of the resin, add deionised water.
Cations from the sample solution shown as (M) displace hydrogen ion on the resin.
The washing carries the resulting acid solution into the conical flask
Periodically test the washings until the indicator shows they are neutral.
The red color indicates that washing must continue.
Any acid test solution must be added to the conical flask.
When the test indicates that the washing leaving the column are neutral, titrate the acid effluent collected in the large conical flask against standard alkali using screened Methyl Orange as the indicator.
The titre will give the acid equivalent of all the cations contained in the 25cubic cm of sample solution.

COLUMN CHROMATOGRAPHY

Column chromatography is a preparative technique used to separate and isolate pure compounds in multi-components reaction mixtures.
The solvent to be used in bulk chromatography is determined using thin layer chromatography TLC.
The solute spots in the left hand plate have hardly moved from the start line because the solvent system was not polar enough.
Whereas the spot have too far in the right hand plate because the solvent system was too polar.

The centre plate demonstrates a good separation of products in the mixture.
Select a straight column equipped with the tap and clamp it firmly in the stand. If the column has a sintered glass frit at the base, it’s ready to use.
Otherwise a glass wool plug must be place in the column to stop the solid phase clogging the tap.
When using organic solvents, the tap must not be greased because the grease will be leached by the solvent. A plastic tap is ideal.
There are a number of ways of preparing columns for chromatography, but they all have the same aim. To produce a column that is free of air bubbles and voids.

In this common method, first add a little solvent to wet the fret and leave sufficient solvent above it to stop it running dry.
Even if the tap is opened, the fret will only allow running out very slowly.

Next, make up slurry of conical flask by adding solvent to a solid phase such as silica gel.
The amount of solid must be sufficient to fill the column a third full.
Swerve the flask to suspend the solid and release any air bubbles.
Then pour the slurry into the column through a funnel.
Add a little more solvent to give a reservoir above the solid.
Then use a Pasteur Pipette to recycle the solvent washing down the inside of the column while the solid settles.
Any air bubbles can be released by gently tapping the sides of the column.

Use compressed air from a laboratory airline or from a cylinder to force the liquid to just above the top of the column of solid.
Then introduce the crude reaction mixture. This should have been dissolved in a minimum of the chosen solvent or if it not sufficiently soluble, in another compatible solvent.
Run the sample solution down the glass walls to prevent disturbing the top of the column.
Use a little solvent to rinse out the flask and to wash the sample off the wall of glass column.

Connect up the compressed air and force out the excess solvent so that the reaction mixture in the top layer of the silica gel column.
Remove the air line and close the tap to stop the top of the column running dry.
Then to provide reservoir of eluent, completely fill the vessel with solvent taking care not to disturb the surface of the silica gel
With some solid phases, it can be helpful to top the column with a thin layer of sand to minimize any disturbance of the solid surface when solvent is added.

Refit the airline and open the tap.
If a suitable solvent has been chosen, the initial eluent will contain no sample fractions and can be collected in a conical flask.
Well before the initial fractions are due to come off the column, briefly close the tap, then start collecting the eluting fractions in numbered tube or flasks.
The volume in each fraction will vary according to the scale of the separation.
It is undesirable to keep closing the tap during the elution and with good organization; it should be possible to collect the fractions without doing so.

If all the components of the mixture are colorless and there is no other way of judging the progress if the separation, fractions should be collected from the beginning of the elution.
When the elusion is complete, close the tap and analyze the fraction by thin layer chromatography.
If it’s necessary to use more than one plate, it’s important to overlap the fractions making the last fraction on one plate the first on the next.
Well separated bands of single spots indicate a successful separation.
Combine all the fractions with the same component into a pre-weighed round bottom flask.

Dry off the solvent using a Rotary Evaporator.
Then re-weigh the flask and record the yield.

THIN LAYER CHROMATOGRAPHY

Thin Layer Chromatography is a non destructive method of analyzing the number of components in a mixture.

It can be used during the reaction to monitor its progress and at the end of the reaction to access the purity of the product.
The heart of the technique is the chromatography plate which comprises special silica gel coated unto a glass, aluminum or plastic plate.

Small plate with thin coatings about a quarter of a millimeter thick is used for analytical work.
And these are usually kept in an oven or a desiccators to maintain their activity.

The choice of solvent is crucial to a successful TLC separation.
Non polar compounds require non polar solvents.
Polar compounds require polar solvents.
Frequently, a mixture of solvents is used which is tailored to the compound under investigation.
Take a prepared glass or aluminum plate or cut a piece of the appropriate size from a plastic plate.
Mark on it a line in pencil for the start line or origin.
This should be at about 1cm from the bottom edge. Do not use a ball point.

Place of small spots of liquid or solution of solids onto the start line using a drawn capillary tube.
Do not use a dropping pipette or melting temperature tube because these give spots much larger than the 2-3mm diameter required.
Use a fresh capillary for each solution to be spotted unto the plate.
Allow the spots to dry using air blower, compressed air or waive the plate about to dry it.
But do not breadth on the plate to dry them.

If the liquid samples is very dilute several spots may be applied
Wait for the solvent to evaporate before adding another spot.
Note the location of each sample as soon as it’s being applied.
Take a small screw cap bottle or a larger tank and cut a piece of filter paper to go into it.

Pour some of the eluting solvent over the filter paper.
Ensure that the filter paper dip into the solvent but the depth of the solvent is not so deep as to cover the spot on the plate.
Because the solvent used for TLC are often volatile and flammable, a TLC tank should be used in a fume cupboard.

Put the plate into the bottle or tank with a pair of tweezers taken care that the edges of the plate do not touch the sides of tank or the filter paper and that the solvent does not cover the spot on the plate.
Put the lid on to allow a saturated atmosphere of solvents to develop in the tank.

Over a period of time, the spot move up to the plate by capillary action as evident by the dark shadow of the solvent front advancing up the plate.
When the solvent front has almost reached the top of the plate, carefully remove it from the tank with tweezers and mark the edge of the plate the place that the solvent front has reached.

Allow the plate to dry in air or blow it dry with an air blower.
Some spots may be seen with the naked eye but others are revealed under ultraviolet light or by chemical staining for example using an iodine jar.
By dipping or spraying which is often followed by heating to develop the colors?
The utmost situation occurs when the spots travel about a halfway up the plate.

If the solvent is too polar, the spots end up close to the solvent front at the top of the plate.
In this case, a fresh plate should be eluted using a less polar solvent.
Very little travel means the eluting solvent was insufficiently polar. This time, the same plate can be used again with a more polar solvent.
Such reuse takes advantage of the non destructive nature of TLC
A problem often encountered in TLC is the presence of over spots.
This is called TAILING

Tailing indicates that the plate has been overloaded and can be overcome by spotting fewer compounds.
When monitoring a reaction, add the reference spot of the starting material alongside each spot of reaction mixture.
The initial plate shows that the reaction is yet to commence as the sample spot on the right is the same as the starting material reference spot on the left.

Later, two new spots indicate the presence of two reaction products.
Later still, reduction of the starting material spot shows that the reaction is well advanced.
And finally, its removal shows the reaction is complete.
The movement of the spot B relative to the solvent can be used to give information about substance B.

Carefully measure the distances X and Y to give a value X/Y which is the Rf value of B for this particular solvent.

THERMOGRAVIMETRIC ANALYSIS

Thermo gravimetric analysis commonly abbreviated to TGA is a technique used to accurately study changes in weight of substance when heated at a control rate or held isothermally at higher temperatures.
Usually there is a weight loss as a volatile product is produced.
For example when copper sulphate crystal s is heated they lose their blue coloration and there is no complete weight loss.
The addition of water regenerates the initial complex showing that the volatile product in this case is water.
TGA equipment varies considerable. It is often controlled from a single processor.

A typical set up will also have a printer a visual display unit or a plotter, a computer and a controlled supplier gas.
This is the heart of the equipment.
At the top is a sensitive balance that can weigh samples while in their temperature control environment provided by the cylindrical furnace position below the balance.

In this instrument, the balance has two pans.
Above is an easily assessable top pan where empty crucibles can be weighed or tared then re-weighed after the sample has been added.
Beneath the top pan, there is a suspended pan, this is where the sample is weighed during heating.
To heat the sample the furnace is raised around the sample crucible on the suspended pan, typically temperatures up to 10000C can be achieved.

Weight change as small as 0.1micogram can be detected. As with all balances it is important to check that the balance is level.
Since a crucible may need to be re used, it is essential that it is clean at the start of each round, after removal of the lose deposit, this can be achieved by heating the crucible to red heat over the Bunsen.
Any residual discoloration after this treatment will have no effect on the accuracy of the subsequent results.
If the sample produces volatile product, it is normally carried away in an inert gas stream through the exhaust tube; here it is the transparent tube.
Start by checking that all the gas valves to the instrument and the cylinder valves are closed.
Then open the high pressure valve on the cylinder and check whether there is sufficient gas in the cylinder to complete the round.
A reading of more than 500 indicates sufficient gas, in this case di-nitrogen.

Open the low pressure valve and check the gas flow.
Then connect the gas delivering tube to the instrument.
 With some samples reactive gases such as O2 or C02 may be used instead of an inert gas.
Adjust the control valve on the instrument to set the required gas flow as shown by the flow meter.
Purge the instrument for at least 5min.
The gases from decomposition may be toxic, so check that the exhaust tube is in place and is secured.
The exhaust tube should pass through a carbon trap to absorb any toxic materials.

Then set the temperature program conditions.
It’s best to start with the trial run using a rapid heating rate in the wide temperature range.
For a copper sulphate sample, set the starting temperature at 500C.
The rate of heating to 500C per minute
And the high temperature limit at 9500C
A long run time has no advantage so do quick calculation of the expected run time with the lower limit set at 500Cand upper limit set at 9500C.
Then a heating rate of 50 deg per minute gives a run time of 18 minutes.
This is a reasonable run time.
Grind the sample to a powder in a pestle and mortal. This ensures homogeneity and quick thermal contact.

 Because the sample surface area can affect TGA result, sometimes samples such as catalysts, polymers, and fibers need to be measured in the form in which they are received.
Open the balance window and using tweezers, place a clean empty crucible on the balance pan.
Close the window and set the balance to zero to tare the crucible.
Remove the crucible and add the sample. About 10mg is normal a suitable amount.

Replace the crucible on the balance pan.
Close the window and observe the weight of the sample.
If the weight of the sample is satisfactory, adjust the gas flow if necessary and check that it is constant.
Lower the furnace and carefully transfer the crucible to the suspended balance pan.
Raise the furnace and lock it in position.
Then when the balance is settled down, observe the sample weight again.

Start the heating program and observe the changes on the VDU.
Here, the output has been speeded up to save time
An advantage of the VDU output is that it can be rescaled during the run to optimize he display.
When the run is complete, the data is normally saved on the computer
Note the Final weight of the sample.
The TGA trace called the thymogram shows several points
The first point to note is the onset temperature at which weight loses begins.

This is followed by several steps depending on the nature of the sample
In this trial run, there is high temperature decomposition above 6000C as well as lower temperature effect.
When the instrument is cooled, open up the furnace.
Remove the crucible and note the appearance of the sample.
In this case, the black appearance shows that degradation beyond the simple lose of water molecules has taken place
This degradation is the event of curing above 6000C and the trial thymogram shows that to examine the dehydration effect more closely, a second run at a slower heating rate is needed up to a limit of around 3000C
Set the starting temperature as low as possible - 30 deg,
Set the heating rate at 20ged per minute and the final temperature to 300.
Again, do a calculation to make sure the run time is satisfactory which it is at 13.5 minutes
Now repeat the run using a clean crucible and a fresh sample of copper sulphate using the new run conditions.
The thymogram shows that the weights lose due to dehydrations takes place in 3 stages.

The exact position of the steps is not that easy to see. These changes can be enhanced by taking the first derivative of the plot with the troughs mark the exact position of the steps
Using the first derivative can be particularly helpful in analyzing thymograms in which more than one effect is taking place
Here the computer uses the data to perform a step analysis which clearly shows that the dehydration weight changes have a ratio of 2:2:1
When it is cooled, open the furnace.
Remove the crucible and clean it ready for the next user.

Finally, turn off the gas supply.

USING ATOMIC ABSORPTION SPECTROPHOTOMETER

The atomic absorption spectrophotometer is widely used to measure low concentrations of metal ions in aqueous or organic solution.
The parts of the spectrometer are the source of light, which is specific to the element to be determined.
A flame into which solutions are sprayed, converting the meter of their constituent atoms which absorb light at their characteristic wave length.

This absorption is measured by the reduction in the light falling on the detector that lies to the left of the flame.
Fumes from the flame are drawn off by an extractor.
The very hot flame is formed by burning acetylene with compressed air, this cause the temp. 24000C needed to create atoms.
Such a flame must never be left burning unattended so it is important to know how to turn in on or off safely.
To start, turn on the extractor, then at the instrument switch on the compressed air, and adjust the flow to the rate advised in the laboratory note.

Turn the acetylene on at the cylinder, check that the pressure is sufficient to sustain the flow to the flame; here it should be in the white region of the diagram.
Note of the red region must be avoided as this high pressure can cause acetylene to polymerize.
Also note that the cylinder pressure must be at least to 100 pounds per square inch, otherwise the acetone in which the acetylene is dissolved will escape affecting the result.
Switch the acetylene on at the instrument, and adjust the valve to the recommended settings.
Allow 5 seconds for the acetylene to flush out the pipe work, then press the ignite button to light the flame.
Varying the acetylene flow rate varies the characteristic of the flame.
 A higher flow rate gives a rich luminous flame.

 For the determination of copper, select a lean flame. With distilled water aspirating leave the flame burning for 10min, to enable the flame temperature and instrument conditions to stabilize.
Check the correct lamp for the element to be determined is fitted.
The cathode of this discharge lamp is made from element of interest, and its shape gives its name the hollow cathode lamp.
The current through the lamp is set to that recommended by the manufacturers.
A monochromator is used to isolate the light from the lamp from that due to the flame. Set it to the characteristic of the wavelength of the element.

Switch the meter from the lamp to read energy, and fine tune the wave length watching the energy meter as you do so until the meter reads a maximum when adjustment is exactly right.
But enough light may not be reaching the detector; the energy meter needle should be read in the green band.
If not, adjust the flame until it does, too much light will burn out the detector, too little cannot be measured reliably.
The instrument is calibrated using a set of known concentrations of the elements to be analyzed.

The concentration of these standards should be chosen so that the expected concentration of the unknown lies in the middle of the range.
Working with trace concentrations, it is vital that the glassware, water and chemicals used are scrupulously clean and pure.
The absorbencies of the standard solutions and that of the unknown are measured relative to a blank.
This contains exactly the same materials use to make the standard solution except the element to be analyzed in this case, pure deoinised water.

When the instrument stabilizes and aspirating the blank solution, set the instrument absorbance reading to zero by pressing the auto zero button.
Then aspirate the weakest standard solution within a few seconds the reading will stabilize which should read greater than zero, since there are now atoms absorbing in the flame.
Record this value, and then aspirate the remaining standard in turn re- zeroing the instrument between measurement by aspirating the blank solution and pressing auto zero again.
Now aspirate the unknown solution and record the absorbance reading.

Plot a graph of the absorbance readings of the standard solution against their concentrations.
Plot the absorbance of the unknown on the calibration graph and read off the concentration.
Before switching off, aspirate distilled water for 5min to rinse up the capillary and the mixing chamber.
Turn down the acetylene slowly to zero on the instrument fuel tank, and then close the main valve on the cylinder.
Switch off the compressed air and then the extraction fan.
Finally turn down the lamp current, and then switch off the power to the instrument.

USING A FLAME PHOTOMETER

Many flame photometers are quite simple instruments and they must always be calibrated against standard solutions.
A photometer relatively cool flame is suitable for the excitation of the element from groups 1, 2 and the lanthanides.
Air and gas line are attached to the back of the instrument. In this case the air is supplied by small pump.
The gas supplied passes through a secondary regulator valve before entering the instrument.
Before making any readings, unlock the air valve and adjust the air pressure to the value recommended in the instrument manual, then lock the valve.

The regulated air and gas supplied enter a mobilized unit where they are mixed with the sample solution.
The air flow into the nozzle at the front of the unit draws solution up the pump tube and converts it into a mist.
This then enters the nebulizer where it mixes with the gas.
The nebulizer mixture of gas air and solution is passed to the boiler.
Excess liquid from the nebulizer passes in a stand pipe which stops air and fumes escaping and allows excess liquids to run to waste.

Check regularly that the drainage system is functioning correctly. If it is not, the instrument will not give reliable readings.
The way in which this automated instrument works is best seen with the protective hood around the burner assembly removed.
Switching on the instrument automatically open valve in the air and gas supplies, and this instrument automatically ignites the fume air mixture.

The presence of a flame is sensed by a detector and indicated on the front of the panel.
 If ever the flame is extinguished during operation a signal from the detector shut off the gas supply.
When using older instrument without the safety features, take care to follow the operation instruction   exactly, since there may be a risk of forming explosive gas/air mixtures.
The presence of elements such as the alkaline metals colors the flame, this is the color produced by potassium, and this that of sodium.
The light from the flame passes through window to a photo detector which covers the opening and its normally hidden inside the hood.
This instrument is set up to measure calcium, potassium or sodium.
Movement of the bar moves the flame photos in front of the detector, each of these only let the light of the wave length specific to the element in question to reach the detector.

The rate at which the instrument draws up liquid in aspiration rate should be checked using a blank solution in this case, water at the beginning of the round.
This is easily done by drawing the solution from a graduated vessel. A rate of 1cm3 in about 10seconds is satisfactory.
If the instrument does not aspirate or aspirate very slowly, the nozzle may need cleaning, this can be done by removing the nozzle, taking off the delivery tube and passing a fine wire through the nozzle.

The male knob at the end of the nozzle is used to adjust the aspiration rate this should seldom necessary.
Before starting the run, the flame must be set to give maximum sensitivity to the element that is to be measured.
Ensure that the fuel control is well opened, switch on and when the flame is ignited aspirate the blank solution in this case distilled water.
Use the blank control to set the meter reading to zero.
Then replace the blank solution by dilute solution of the element to be measured, in this case sodium.

Check that the correct filter is in place, and then reduce the flame fume until the meter reading is at the maximum.
 Now aspirate the blank solution again to remove any traces of sodium from the nebulizer.
When the meter readings return to zero, the instrument is ready to be calibrated against standard solutions.
A range of standard solutions should have been made up in advance.
The concentration should be chosen so that likely the concentration of the unknown sample lies in the middle of the range.
Start with the most concentrated standard solution.
When the reading is stabilized uses the coarse, and then the fine sensitivity control to bring the meter reading to the concentration of the standard solution.

Once this is done the settings of the instrument should not be altered until the analysis is completed.
Aspirate the blank solution to clean the nebulizer, and then aspirate the next standard solution.
Note the meter reading, remove the standard solution and aspirate the blank solution again.
Continue with this procedure until readings have been recorded for all the standard solutions.
Now aspirate the blank solution again, and then aspirate the unknown sample, and record the meter reading.
Finally aspirate the distilled water for a couple of minutes to finally clean up the nebulizer, and then switch off.
For non automated instrument carefully follow the shut down procedure.

If the ordinary solution contains solute, it is important to filter it order wise the nebulizer may become blocked.
It is vital to select the filter paper that will not absorb the ion that must be measured, if in doubt seek advice.
Finally wash up the sample vessel and the filter to ensure the entire soluble sample is transfer to the measuring flask, and then make it up to volume.
Plot the calibration reading, this record may give a sign curve that is why calibration is necessary.
Then read off the part per million value corresponding to the analytical sample

USING A ROTARY EVAPORATOR

The rotary evaporator provides a means of removing large volumes of solvent from solution under mild conditions.
It uses reduced pressure so the solvent evaporation temperature required are much lower than those required at atmospheric pressure.
All the apparatus looks complex. Its operation is quite straight forward.
To start, turn on the water supply to this mild condenser.
Next, turn on the water vacuum pump.
Make sure the pressure release verve at the top of the condenser is open.
Notice that the vacuum line is fitted with a trap to prevent water from sucking back.

The sample should be placed in a round bottom flask and should never more than half fill the flask.
Slide the flask unto the ground glass joint and clip it in place.
The joint should not be greased.
Then switch the motor on so that the flask rotates at a moderate pace.
Close the pressure release valve.
Wait about 20seconds while the vacuum builds up.
Then lower the flask into the water bath.
 On this apparatus, the stop on the column is preset so that the flask descends to the correct level.
In some set-up, the water bath is raised to the flask.
Either way, the water level must be no higher than the level of solution in the flask.

Set the temperature of the water bath to give a steady rate of solvent evaporation.
This can be judged by the rate at which condensed solvent trickles out of the condenser into the receiver.
If the rate of solvent removal slows down, increase the water bath temperature.
Should the rate of evaporation become too high, froth may occur.
It can be controlled by briefly opening and closing the pressure release valve.

When most of the solvent has been removed, the product may line the wall of the flask as a solid but often an oil is formed.
Lift the flask from the bath.
Stop the rotation.
Turn off the water bath so it doesn’t boil dry.
Release the vacuum and allow the flask to cool until it can be comfortably handled.
Remove the flask
Place it on a cork ring and stopperd it lightly
Then remove the solvent receiver and empty the content into the appropriate waste solvent container.
Having turned off the cooling water, replace the solvent receiver so that it is out of harm’s way.

Finally, clean up the ground glass joint ready for the next user.
At the end of this procedure, it may be necessary to further purify the product by re-crystallization or distillation.

HEATING SAMPLES

Heating is an essential tool in the chemist armory with several different methods of heating available such as the
Hot plate stirrer and oil bath for distillation for distillations.
The heating mantle for reflux,
The Bunsen burner for dissolving or crystallizing samples,
The steam bath is for dissolving samples or heating reactions.
Before carrying out any heating operation, take time to consider the most appropriate method to carry out the task both efficiently and safely.
First, some general points
Always add anti-bumping granules to liquid before heating them – This reduces the risk of hot liquid splashing out of the vessel and causing scars
Never hold flask or test tube in the hand when heating them. Always use a holder such as a wooden peg.
Or support a flask say by clamping the vessel to retort stand.
Lastly, wear gloves.

BURSEN BURNER
The Bunsen burner is the simplest method of heating which should only be used for non flammable liquids.
Before lighting, close the air hole, connect the tube to the gas supply, turn on the gas and immediately light the gas with the spark igniter.
To avoid the danger of accidental burns, whenever a lighted Bunsen is not in immediate use, the air hole should be close to give a luminous yellow flame since this is not easily overlooked.
To adjust the temperature, open the air hole for a hot flame,
Close it to cool the flame.

To heat a flask, clamp it standing on a wire gauze fitted to a tripod.
Add anti-bumping granules.
Then position the lighted Bunsen under the tripod
The gauze spreads the flame and helps prevent erratic boiling.
To begin with, heat cautiously with a cool blue flame not a luminous yellow flame as this will deposit sooth. Then slowly increase the heat.
If boiling becomes too vigorous, close the air hole slightly to cool the flame.
Vary the setting until steady boiling is achieved.
If a liquid is to be heated to a temperature less to boiling, clamp a thermometer so the bulb is suspended in the liquid.
Heat slowly to the desired temperature, then adjust the flame to maintain that temperature.
Test tubes can be heated directly in a Bunsen burner but heat cautiously at the edge of the flame to begin with, constantly moving the tube in the flame to prevent bumping and splashing.
Always ensure that the open end of the test tube is pointed from yourself and other workers.
To increase the heat, move the test to the heart of the flame just above the blue cone but never hold the tube motionless.
When finished, place the test tube in a beaker or test tube stand.
Pear shaped flasks can be heated directly but it is important to keep the flame moving around the flask below the level of the liquid.
Small micro-Bunsen is best for this purpose.

STEAM BATH
Steam bath are commonly used for gentle heating to temperature below 100degrees
Nevertheless care is needed due to the risk of scolding.
Usually, they are electrically heated and it is important to maintain the water level in the bath.
Many baths have drip fixed with drawn off pipes which automatically maintain the level constant.
It’s safest to set up the apparatus before the heating the bath.
Remove the inner metal rings until the flask fits well down in the recess.
The flask should be suspended so that there is a small space within it and the ring.
This will allow a gentle flow of steam to pass up around the flask.
Test tubes can be heated in open cups.
Conical flask can be placed directly on open cups.
But remember that moisture will condense on the equipment so don’t use steam bath for moisture sensitive compounds

STIRRER HOT PLATE
Stirrer Hot Plate can be used to heat non flammable liquid in conical flasks and have the advantage of stirring can be accomplished with a magnetic stirrer bar.
The agitation from the stirrer removes the need to add anti-bumping granules.
There are two control knobs, one controls the heating rate and the other controls the stirring rate.
Start with the heated control at the middle of its range.
Several adjustments may be necessary before a steady rate of boiling is achieved.
If the liquid is to be heated to a temperature less than boiling, then a thermometer can be suspended in the flask but be very careful to keep the bulb away from and above the magnetic stirrer bath.
When finished, turn down the heating control and wait until boiling has ceased.
Then turn off the stirring and raise the flask from the hot plate so that it cools more quickly.
Don’t try to remove the flask until it is cooled sufficiently to handle.
Never leave a hop plate to cool down without some indication that it is still hot.
Some hot plates have indicators which swing out in response to heat that act as a warning
In the absence of such indicator place a beaker of cold water on hot plate to speed the cooling and to warn other workers that the hot plate in been in use.

A hot plate stirrer is often combined with the heating bath which normally contains a non volatile paraffin or silica oil.
But water can be used for bath temperature up to 800C.
Set the bath so that the level of liquid in the flask is just below that of the oil.
Don’t overflow the bath and clean off any liquid split on the outside of the bath.
And as a further protection to the hot plate, cover it with foil.
Turn on the stirrer motor and slowly increase the rate of stirring.
Switch on the heat, monitoring the oil temperature with a thermometer clamped to position.
Heat strongly until the temperature of the oil is 10 – 20 degrees above the temperature required in the flask.
Adjust the heating until the bath settles at this temperature.
Then of a period of about 15min, regularly check the bath temperature to ensure that it is stable.
Oil bath always have a upper temperature limit normally about 2000C depending on the type of oil
D not exceed this limit as obnoxious fumes can be produced.
When finished, switch off the heater and stirrer controls.
Raise the vessel above the bath and allow it to cool. Residual oil on the flask will drain back into the oil bath.
Once the reflux has ceased, remove the condenser.
When the flask is cooled, wipe off excess oil with a tissue so that no oil drips on to the hot palte and the flask isn’t slippery
Then remove the flask.
The oil bath should be left on the hot plate to cool completely before being removed.
Alternatively, the hot plate and bath can be supported on a lab jack which can be raised or lowered as required.

HEATING MANTLES
Heating Mantles are suitable for heating round bottom flasks containing either flammable or non flammable liquids in processes such as reflux but they are not well suited for distillation.
The flask containing the materials and a few anti-bumping granules should fit snugly into the mantle.
If refluxing, fit a condenser. Turn the heater control to half way and wait for 5 – 10mins.
If boiling does not take place, increase the heating in stages until it does.
At the first sign of boiling, turn down the heat slightly.
Continue to adjust the heating control until gentle reflux is achieved.
When finished, switch off the heating mantle, and leave the apparatus to cool before dismantling.
The necessary ventilation in a fume cupboard can produce a strong draft. So when heating in the fume cupboard, always check that the temperature is stable after the window is being lowered.

USING STIRRER

Stirring is one of the most frequently used techniques in chemistry.
In homogenous systems, it’s used to facilitate mixing and heat transfer and for agitation.
In heterogeneous systems, for renewing liquid-liquid and liquid-solid interphases.
The most versatile system and also the simple to use is the magnetic stirrer.
Which commonly also include hotplate for combined heating and stirring
Stirring rates are controlled by a variable speed motor driving a rotating bar magnet.
This in turn drives a magnetic stirrer bar, sometimes called a flee or follower.
The heating element and the stirrer have independent controls.
The remaining types of stirrer bar, different sizes and shape are designed to suite a range of different vessels.

Take care to choose the right size. This bar is too big. It should be able to rotate on a central ridge.
This is the correct size.
The stirrer bar should always be introduced into the reaction flask first, sliding it gently down the side rather than dropping it straight into the flask.
After adding the reagent, turn on the motor and adjust the speed of stirring to obtain good agitation but without splashing.
A stirrer that behaves erratically may not be centered over the motorized magnet or the motor speed may be too high.
Turn off the stirrer waiting till the stirrer bath settles, then slowly increase the speed repositioning the vessel if necessary.
For stirring reflux, choose a stirrer bar of such a size that can turn easily inside the flask.

The position of the flask in the heating bath may present a problem because the magnetic range of the motorized magnet is limited.
Lower the flask into the heating bath until the stirrer works efficiently.
If necessary reduce the amount of liquid in the bath.
Viscosity decreases with temperature, so occasionally check the speed of stirring as the liquid warms up.
Magnetic stirring is particularly used for reactions that need to be carried under dry or oxygen free conditions.

Mechanical stirrers are used for agitating bath and when a magnetic stirrer may not be powerful enough to maintain efficient stirring.
Top mounted electric motors must be attached to tall and stable stands.
The motor usually has an on-off switch and a variable speed setting.
A piece of thick rubber tubing provides a simple and slightly flexible way of attaching the stirrer rod.

When a rigid system is acceptable, a drill choke can be used. This is useful when particularly powerful stirring is required.
A range of materials and much ingenuity is being used in devising stirrer rod and paddles that are suitable for a wide range of applications. Some are designed for specific vessel shapes.
 Others are more adaptable.
First select the stirrer that will enter the neck of the flask and with the paddle profile to suite the shape of the flask.
If a reaction needs a controlled atmosphere, a ceiling gland must be fitted to the stirrer rod. The most common is the oil-cup seal.
The sleeve inside the cup should be a close but not a tight fit to the stirrer rod.

The other part of the seal, is another sleeve with a screw gland.
To attach the stirrer, first lower the motor and secure it just above the rod. And carefully push the rod into the holder.
Now slowly lower the assembly. Secure the motor clamp when the paddle is just above the base of the flask.
And tighten the screw gland so that it gives an air tight seal.
Start the motor running slowly and check that everything is running smoothly.
Turn off the stirrer and top up the oil in the cup.
There should be about a centimeter of oil above the bottom of the sleeve.
If the stirrer doesn’t operate smoothly, try repositioning the flask until it does.
Switch off the motor, then, add any other pieces of apparatus that are required.

Finally, check again for smooth operation and make any necessary adjustments before adding reagents and starting the reaction.
There are a number of ways of attaching motor to stirrers. But the set up and adjustment procedures are very similar.
Equally, there are a number of different sealing mechanisms.
A simple seal can be made with a sharp piece of thin wall rubber tubing but remember that it must be lubricated with little oil.
Note that oil causes rubber to perish so such seals can only be used once.

ASSEMBLING APPARATUS

Chemical glassware are connected together using quick fit or conned socket joints.                                      
These come in various sizes named B14, B19, B24 and so on.                
But all of them have the same tapper so that cones and sockets of the same number fit together exactly.
In cases where it is necessary to join cones and sockets of different sizes, adapters are available.
Joints may be secured using plastic clips but this should not be relied upon to support the apparatus.

The clips are color coded according to the size of the joint they are designed to secure. It’s not often necessary to grease joints provided the glassware is going to be dismantled immediately after use.
A greasing is advisable for distillation under reduced pressure, for reaction under strictly anhydrous conditions and if a steam is used for heating. A light smear of grease should be applied on to the curve of the cone.

Never apply grease to the socket as it may be forced inside the apparatus contaminating the contents.
An alternative to greasing is the use of PTFE sleeves.
Tubing should never be forced over the glass side arm of the condenser. Side arms are easily broken and may cause injury.
The rubber tubing under glass should be wetted. Then the tubing will slide on easily.

Tubing should always pass well beyond the widest part of the side arm.
Soften plastic tubing by immersing it in hot water.
It will then slip easily unto the side arm.
Some condensers have detachable side arms which are attached to the condenser with the screw cap.
With this design, first put the tubing on the side arm, and then attach the side arm to the condenser.

Glass apparatus is support by metal clamps fixed to stand by bosses.
A boss is always attached to a stand so that the channel holding the stem of the tap faces upward providing freedom when the position of the stem is adjusted.

If the channel points downwards, the clamp can easily fall out of the boss during adjustment.
A clamp have fixed and adjustable jaws. It’s best to have the adjustable jaw on the stand side of the boss.
This way, the apparatus is supported centrally over the base of the stand and there is no danger of the stand toppling over.
When supporting a horizontal piece of glassware like a condenser, the opening jaw must be uppermost.
In this position, the apparatus is supported on the fixed jaw during adjustments.

If the moveable jaw is underneath, the whole apparatus will sink during adjustment and there is a danger it will fall out.
When setting up apparatus for distillation, always start by clamping the flask firmly but not too tightly.
Its position is adjusted using the boss screws one at a time.
Clamp screw for back and forth and to ensure the flask is vertical.
Stand screw from side to side or up and down.
Never support apparatus by clamping an adapter.
For distillation, the flask is connected to the condenser with the distillation head.

For simple distillation, joints are not greased.
Check that the condenser fits snugly unto the distillation head and secure the joint with the clip.
Connect a receiver adapter or takeoff band to the outflow of the condenser. Again, secure the joint with the glassware clip.
Support the receiving flask using a cork ring or lab jack.
When a steam bath is used as the heating source, condensate will collect on joints. And to prevent water sipping inside the apparatus, the joints must be greased.

A reflux condenser should always be supported using a second clamp and boss on the same stand.
Adjust the position of the clamp and rotate it on the stand until the condenser rest against the fix jaw of the clamp.
The clamp should not hold the condenser tightly. Its purpose is to prevent the condenser toppling sideways.
Add a drying tube with a lightly greased joint if the reflux is to be performed under anhydrous conditions.
In the reflux apparatus, all components are held together by gravity. So glassware clips are not needed.
It is essential to secure tubing if the experiment is to be left unattended over lunch or overnight.

Both rubber and plastic tubing should be secured with wire.
Alternatively, plastic ties can be used in place of wire.
Even when tubing has been secured, if the apparatus is to be left unattended, it must always have a safety card leaving necessary information for an emergency shutdown.