Question

Slaked lime, $ Ca{{(OH)}_{2}} $ is used extensively in sewage treatment. What is the maximum pH that can be established in $ Ca{{(OH)}_{2}}(aq) $ ? $ Ca{{(OH)}_{2}}(s)C{{a}^{2+}}(aq)+2O{{H}^{-}}(aq); $ $ {{K}_{sp}}=5.5\times {{10}^{-6}} $

• A. 1.66
• B. 12.35
• C. 7
• D. 14

Answer 1

Answer: (B)

$ {{K}_{sp}}=5.5\times {{10}^{-6}} $ $ Ca{{(OH)}_{2}}C{{a}^{2+}}+2O{{H}^{-}} $ $ \therefore $ $ {{K}_{sp}}=[C{{a}^{2+}}]{{[O{{H}^{-}}]}^{2}}=5.5\times {{10}^{-6}} $ $ \Rightarrow $ $ 4{{s}^{3}}=5.5\times {{10}^{-6}} $ $ \Rightarrow $ $ s=0.0111 $ $ \therefore $ $ [O{{H}^{-}}]=2s=0.0111\times 2=0.0222 $ $ pOH=1.65 $ $ pH=14-1.65=12.35 $