Question

Compare the acidic nature of $0.1M$ $HCNO$ with that of $0.2M$ $HCN$. Given $K_a$ for $HCNO=1.2\times {10}^{-4}$ and $K_a$ for $HCN=4.0\times {10}^{-10}$ at $298K$.

• A. HCNO solution is $2.6\times {10}^{-3}$ times more acidic
• B. HCNO solution is $3\times {10}^5$ times more acidic
• C. HCNO solution is $3.9\times {10}^2$ times more acidic
• D. none of these

Answer 1

Answer: (C)

HCNO solution is $3.9\times {10}^2$ times more acidic

As we know,

$[H^{+}{]}_1=[C_1\times \alpha {]}_1=\left[\sqrt{K_{c1}\times C_1}\right]$

$\left[H^{+}\right]=[C_2\times \alpha {]}_2=[\sqrt{K_{c2}\times C_2}]$

Given,

$K_a$ for $HCNO=1.2\times {10}^{-4}$ and

$K_a$ for $HCN=4.0\times {10}^{-10}$

So acidic nature of

$\frac{[HCNO{]}_1}{[HCN{]}_2}=\frac{[C_1\times \alpha {]}_1}{[C_2\times \alpha {]}_2}\approx 3.9\times {10}^2$

So, HCNO is more acidic than HCN.