If p K b for C N - at 25 o C is 4.7, the pH of 0.5 M aqueous NaCN solution is

Question

If p K b for C N - at 25 o C is 4.7, the pH of 0.5 M aqueous NaCN solution is, 10, 11.5, 11, 12

MARKS App · Accepted Answer

p k b o f C N - = 4.7 p k a o f H C N = 4.7 N a C N is salt of weak acid H C N and strong base N a O H So p H = 7 + 1 2 p k a + 1 2 l o g C = 7 + 1 2 × 9.3 + 1 2 log ⁡ 0.5 ∴ p H = 11.5

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