Question

Why must the silver nitrate test for chloride ions be done in an acidified solution?

Answer 1

Because silver, like most of the heavier metals, forms an insoluble hydroxide.

Explanation:

In order to determine the presence of the halide, competing equilibria must be taken into account. Silver forms an insoluble hydroxide, which is probably a hydrous oxide. When `pH` is lowered from `7`, this competing equilibrium is removed, any chloride will precipitate as a curdy white solid as `AgCl`, as a lemon-yellow solid as `AgBr`, and as a bright yellow solid as `AgI`.

The acid of choice would be `HNO_3(aq)`. Why do we use this acid and not say `HCl(aq)` or `HBr(aq)`?