Question

In the test for Cl1- and SO4 2- , explain why the addition of acid will dissolve or decompose other silver salts and barium salts, which otherwise might Interfere

Answer 1

Strong acids can dissolve the salts of weak acid. When we consider the different salts of silver:

Salts of silver with the conjugate bases of a weak acid are soluble in strong acidic solutions. Some of these salts are:

`2Ag^(+)(aq)+CO_(3)^(2-)(aq) --->Ag_(2)CO_(3)(s)`

`Ag^(+)(aq)+C_(2)H_(3)O_(2)^(-)(aq)-->AgC_(2)H_(3)O_(2)(aq)`

`2Ag^(+)(aq)+SO_(3)^(2-)(aq) --->Ag_(2)SO_(3)(s)`

Salts of silver with the conjugate bases of a strong acid are not affected by change in pH:

`Ag^(+)(aq)+Cl^(-)(aq) --->AgCl(s)`

`2Ag^(+)(aq)+SO_(4)^(2-)(aq) --->Ag_(2)SO_(4)(s)`

These two salts with Chloride and sulfate ions are not soluble in acidic solutions as the salts of silver with the conjugate bases of a strong acid are not soluble in acidic solutions, they remain unaffected by any change in pH.

So for salts of Ag and Ba with the conjugate bases of a weak acid, solubility is increased upon the addition of an acid. So, the interference from the ions of weak acids can be removed by decreasing the pH.