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.
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