Question

A certain buffer solution contains equal concentration of $X^-$ and $HX$. The $K_h$ for $X^- \, is \, 10^{ - 19 }$ . The pH of the buffer is

• A. 4
• B. 7
• C. 10
• D. 14

Answer 1

Answer: (A)

4

Answer 2

$K_c ( HX) = \frac{ k_w }{ K_b } = 10^{ - 4}$
pH = $pK_a + \log \frac{ [ X^- ]}{ [ HX ]}$
$\Rightarrow pK_a = 4$ \hspace20mm $[ \because [ X^- ] = [ HX ]]$