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pH at which a metal hydroxide or sulphide begins to precipitate

This type of question, asked 2 times: 30 Jan 2024, 24 Jan 2026 S1. All 2 questions below, oldest first.

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  1. Question 1

    30 Jan 2024

    52
    The pHpH at which Mg(OH)2[ Ksp=1×10−11]Mg(OH)_{2}\left\lbrack {\text{ }K}_{sp}= 1 \times10^{- 11} \right\rbrack begins to precipitate from a solution containing 0.10M0.10M Mg2+Mg^{2 +} ions is ______

  2. Question 2

    24 Jan 2026 S1

    47
    Consider two Group IV metal ions X2+X^{2 +} and Y2+Y^{2 +}. A solution containing 0.01MX2+0.01{MX}^{2 +} and 0.01MY2+0.01{MY}^{2 +} is saturated with H2 SH_{2}\text{ }S. The pH at which the metal sulphide YS will form as a precipitate is ____\_\_\_\_ (Nearest integer) (Given : Ksp(XS)=1×10−22K_{sp}(XS) = 1 \times 10^{- 22} at 25∘C,Ksp(YS)=4×10−1625^{\circ}C,K_{sp}(YS) = 4 \times 10^{- 16} at 25∘C25^{\circ}C, [H2 S]=0.1M\left\lbrack H_{2}\text{ }S \right\rbrack = 0.1M in solution, Ka1×Ka2(H2 S)=1.0×10−21K_{a1} \times K_{a2}\left( H_{2}\text{ }S \right) = 1.0 \times 10^{- 21}, log⁡2=0.30,log⁡3=0.48,log⁡5=0.70\log2 = 0.30,\log3 = 0.48,\log5 = 0.70 )