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Consider the dissolution equilibrium of sparingly soluble Zn(OH)2 in water with Ksp = 4 * 10⁻¹². Which of the following statements are correct? I. The solubility of Zn(OH)2 is 10⁻⁴ mol/L. II. Adding a small amount of OH- ions decreases the solubility. III. Adding concentrated HCl increases the solubility. IV. In the presence of 0.01 M ZnCl2, the solubility of Zn(OH)2 becomes 10⁻⁵ mol/L.

1. I and II only
2. I, II and IV only
3. I and IV only
4. I, II, III and IV

Correct answer: I, II, III and IV

Solution

Statement I: Ksp = (s)(2s)² = 4s³ = 4*10⁻¹², so s³ = 10⁻¹², s = 10⁻⁴ M. True. Statement II: Common ion OH- shifts equilibrium left, reducing solubility. True. Statement III: HCl neutralises OH-, removing it from solution, shifting equilibrium right, increasing solubility. True. Statement IV: Ksp = (0.01)(2s)² = 4*10⁻² * s² = 4*10⁻¹², s² = 10⁻¹⁰, s = 10⁻⁵ M. True. All four are correct.

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