MCQ
When $CO_2$ dissolves in water, the following equilibrium is established

$C{O_2} + 2{H_2}O\, \rightleftharpoons {H_3}{O^ + } + HCO_3^ - $

for which the equilibrium constant is $3.8 \times 10^{-7}$ and $pH = 6.0$. The ratio of  $[HCO_3^- ]$ to $[CO_2]$ would be :-

  • A
    $3.8 \times 10^{-13}$
  • $3.8 \times 10^{-1}$
  • C
    $6.0$
  • D
    $13.4$

Answer

Correct option: B.
$3.8 \times 10^{-1}$
b
$\mathrm{Ka}=\frac{\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\left[\mathrm{HCO}_{3}^{-}\right]}{\left[\mathrm{CO}_{2}\right]}$

$\frac{\left[\mathrm{HCO}_{3}^{-}\right]}{\left[\mathrm{CO}_{2}\right]}=\frac{\mathrm{Ka}}{\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}$

$=\frac{3.8 \times 10^{-7}}{10^{-6}}=3.8 \times 10^{-1}$

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