[Hand15]

Weeks ago our class do some titrations using reference electrodes. Well it's just ordinary titration and I have no problem with that. But something different with this titration is that the reference electrode we used is made by ourselves which I think very frustrating (partly because we haven't learn anything about reference electrode).

The reference electrode we made is Silver Chloride Electrode. Basically we use a small cylinder with porous bottom in one end and fill it with agar (the agar is made with 25mL of water + 3 g agar + 14 g KCl; not all the agar was used of course); then add small amount of KCl(s) on the agar layer, and fill it with saturated KCl solution; after that add 1 to 2 drops of AgNO3 (a white precipitated AgCl will appear); and then close the cylinder with rubber bung where a thin silver stick is attached to it.

It seems easy... but well the electrode leaked (the majority of my classmates also fail to prevent it from leaking)
We test the electrode by placing it to AgNO3 solution. If there are white AgCl produced in the AgNO3 solution, then good luck for your next try  ...


And I have to repeat those steps for 2 hours (I don't remember how many electrodes I have made, probably around 15 or more). Fortunately after an exhausting 2 hours, the electrode didn't leak at last (Praise God!)

My question is why this self-made electrode often leak? Is it because of the agar? Or something else? And I don't understand why we must add small amount KCl(s) and 1~2 drops of AgNO3 there.