Question

Which of the following sulphate is insoluble in water?
A. $CaS{O_4}$
B. $CdS{O_4}$
C. $PbS{O_4}$
D. $B{i_2}{(S{O_4})_3}$

Answer 1

Almost all ionic compounds are soluble in water. Some are very soluble like NaCl, KBr and some are slightly soluble. But under extreme conditions, sometimes not soluble.

Complete step by step answer:
$CaS{O_4}$ is slightly soluble in water. It is soluble in water which is cold but insoluble in hot water. This means that the heat evolved during the dissolving process is greater than the heat required to break the solid bonds apart.
Cadmium sulphate is highly soluble in water due to the size difference of Cadmium and sulphate ions. Moreover,$CdS{O_4}$ compound is a hydrogen bond acceptor compound and hence can easily form bonds.
Lead sulphate ($PbS{O_4}$) is insoluble in water because water's dipole strength is too weak to pull away the ions (both anions and cations) from the strong crystals of lead sulphate.
Bismuth paper with a chemical formula of $B{i_2}{(S{O_4})_3}$ is moderately soluble in water.
Hence, option (C) i.e. lead sulphate ($PbS{O_4}$) is insoluble in water.

Note:
Lead sulphate occurs naturally in the mineral anglesite. It is synthesised by adding sulphuric acid to lead salt solution lead sulphate is used in lithography and in weighting fabrics.