Question

Explain why solubility of Pb(BrO₃)₂ in water is different from its solubility in 0.100 M KBrO₃.

Answer 1

In aqueous solution, lead(II) bromate sparingly dissociates to give Pb²⁺ and BrO₃^-.

Pb(BrO₃)₂(s) $\rightleftharpoons$ Pb²⁺(aq)+ 2BrO₃^-(aq)

Potassium bromate is a strong electrolyte. It completely ionizes in water to give K⁺ and BrO₃^-. This BrO₃^- produced by KBrO₃ acts as a stress for the above equilibrium. Hence, to reduce the stress i.e. the BrO₃^- concentration, equilibrium of dissociation shift in the reverse direction i.e. the formation of the precipitate of lead(II) bromate. Hence, the solubility of lead(II) bromate decreases in the solution of KBrO₃. This phenomenon is called the common ion effect. In this case the common ion is BrO₃^-.