Question

Why glass membrane kept in water even after the experiment is over?

Answer 1

The special conductive glass coating shouldn’t be left to dry out… always keep it hydrated, or it may stop working! You can buy special storage solutions for this purpose. Either keep the probe submerged in a falcon tube, or keep the probe covered with the special cap it came with. The exact type of solution used will depend on your meter, as different probes have different requirements. Combined electrodes (those consisting of both the glass and reference electrodes) are typically stored in a concentrated solution of whatever is inside the probe – the concentration should be higher to prevent diffusion out of the probe. pH meters with two separate electrodes can have their glass electrodes stored in an acidic solution of roughly pH 3. In either case, never use distilled or deionized water, as prolonged submersion in water can encourage diffusion out of the electrode, which will affect its sensitivity.

Answer 2

Between measurements any glass and membrane electrodes should be kept in a solution of its own ion. It is necessary to prevent the glass membrane from drying out because the performance is dependent on the existence of a hydrated layer, which forms slowly. Because of the fact that more the hydration more the conducting nature, hence they should not be allowed to dry out.