19. If the solubitity of lead flusride, PoF 2 , is \( 0.64 \mathrm{~g} \mathrm{gme}^{-1} \), what is the value of solubility product?
20. Calculate the solutribry of MnS in
(a) wate
(b) in \( 21.0 \times 10^{-2} \mathrm{~mol} \mathrm{dan}^{3} \) solution of suiptide ion
\[
\mathrm{K}_{\Rightarrow}(\mathrm{MnS})=25 \times 10^{13} \mathrm{~mol}^{2} \mathrm{dm}^{-6}
\]
21. Explaen why, when bytrogen sulphide is passed urto zan acidac solution cortaining \( \mathrm{Ca}^{3-} \) 1005 and \( \mathrm{Fe}^{\text {l- }} \) ions, CuS is precipitated but FES is not precipitated
\[
\mathrm{K}_{\theta}(\mathrm{CuS})=6 \times 10^{-36} \mathrm{~mol}^{2} \text { dens } \quad \mathrm{Ksp}_{\mathrm{p}}(\mathrm{FeS})=6 \times 10^{-2} \mathrm{~mol}^{2} \mathrm{dm}
\]
22. Explain the following observations:
(a) the solubiling of PbCl in water decreases on the addition of ditue byctochlonic acid and increases on the adtition of conceatrated bydrochlonic acid.
(b) The addstion of aqueous ammonia to magoesinen sulphate gives a white procipitate which is soluble in aqueous ammonian chlonde
