1. Tardigrade
  2. Question
  3. Chemistry
  4. An aqueous solution contains Ni 2+, Co 2+ and Pb 2+ ions at equal concentrations. The solubility product of NiS, PbS and CoS in water at 25° C are 1.4 × 10-24, and 3 × 10-26, respectively. Indicate which of these ions will be precipitated first and last when sulphide concentration is progressively increased from zero?

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Q. An aqueous solution contains $Ni ^{2+}, Co ^{2+}$ and $Pb ^{2+}$ ions at equal concentrations. The solubility product of $NiS,\, PbS$ and $CoS$ in water at $25^{\circ} C$ are $1.4 \times 10^{-24}$, and $3 \times 10^{-26}$, respectively. Indicate which of these ions will be precipitated first and last when sulphide concentration is progressively increased from zero?

J & K CETJ & K CET 2008Equilibrium

Solution:

For precipitation, ionic product > solubility product
$\therefore $ The metal sulphide with lowest $K_{s p}(P b S)$
will precipitate out first because its ionic product will exceed its $K_{s p}$
first and the metal sulphide with lowest $K_{s p}(N i S)$ will precipitate out at last.