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Question

Chemistry Question on Acids and Bases

The pHpH of a 0.01 M HCN0.01 \,M\, HCN solution for which pKapK_a is 44 is

A

0.47

B

1.2

C

3

D

4

Answer

3

Explanation

Solution

Given, pKa=4pK _{ a }=4
∴Ka=1×10−4\therefore K _{ a }=1 \times 10^{-4}
[H+]=Ka⋅C\left[ H ^{+}\right]=\sqrt{ K _{ a } \cdot C }
=1×10−4×0.01=\sqrt{1 \times 10^{-4} \times 0.01}
=10−6=10−3M=\sqrt{10^{-6}}=10^{-3} M
pH=−log⁡[H+]pH =-\log \left[ H ^{+}\right]
=−log⁡(10−3)=3=-\log \left(10^{-3}\right)=3