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At 25 °C, the solubility product of Mg(OH)2 is 1.0 × 10⁻¹¹. At which pH, will Mg2+ ions start precipitating in the form of Mg(OH)2 from a solution of 0.001 M Mg2+ ions?

1. 9
2. 10
3. 11
4. 8

Correct answer: 10

Solution

The solubility product (Ksp) of Mg(OH)2 indicates that precipitation occurs when the product of the concentrations of Mg2+ and OH- ions exceeds Ksp. At a pH of 10, the concentration of OH- ions is sufficient to cause the product of Mg2+ and OH- concentrations to reach the Ksp value, leading to precipitation.

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