Only is hydrolysing and its first hydrolysis constant is . — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

The molar mass of potash alum is $39 + 27 + 2(96) + 12(18) = 474\text{ g/mol}$. The number of moles is $11.85 / 474 = 0.025\text{ moles}$. Volume is $100\text{ cm}^3 = 0.1\text{ L}$. Concentration $C = 0.025 / 0.1 = 0.25\text{ M}$. For the first hydrolysis of $\text{Al}^{3+}$: $[\text{H}_3\text{O}^+] = \sqrt{K_h \cdot C} = \sqrt{1.4 \times 10^{-5} \times 0.25} = \sqrt{3.5 \times 10^{-6}} \approx 1.87 \times 10^{-3}\text{ M}$. Therefore, correct answer is A.