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In aqueous solution the ionization constants for carbonic acid are $\mathrm{K}_1=4.2 \times 10^{-7}$ and $\mathrm{K}_2=4.8 \times 10^{-11}$
Select the correct statement for a saturated $0.034 \mathrm{M}$ solution of the carbonic acid.
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Select the correct statement for a saturated $0.034 \mathrm{M}$ solution of the carbonic acid.
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Verified Answer
The correct answer is:
The concentration of $\mathrm{H}^{+}$and $\mathrm{HCO}_3^{-}$are approximately equal.
The concentration of $\mathrm{H}^{+}$and $\mathrm{HCO}_3^{-}$are approximately equal.
$\begin{array}{lll}\mathrm{A} \rightarrow & \mathrm{H}_2 \mathrm{CO}_3 \rightleftharpoons \mathrm{H}^{+}+\mathrm{HCO}_3^{-} & \mathrm{K}_1=4.2 \times 10^{-7} \\ \mathrm{~B} \rightarrow & \mathrm{HCO}_3^{-} \rightleftharpoons \mathrm{H}^{+}+\mathrm{CO}_3^{-2} & \mathrm{~K}_2=4.8 \times 10^{-11}\end{array}$
As $\mathrm{K}_2 \ll \mathrm{K}_1$
All major $\left[\mathrm{H}^{+}\right]_{\text {todal }} \approx\left[\mathrm{H}^{+}\right]_{\mathrm{A}}$
and from I equilibrium, $\left[\mathrm{H}^{+}\right]_{\mathrm{A}} \approx\left[\mathrm{HCO}_3^{-}\right] \approx\left[\mathrm{H}^{+}\right]_{\text {tocal }}$
$\left[\mathrm{CO}_3^{-2}\right]$ is negligible compared to $\left[\mathrm{HCO}_3^{-}\right]$or $\left[\mathrm{H}^{+}\right]_{\text {total }}$
As $\mathrm{K}_2 \ll \mathrm{K}_1$
All major $\left[\mathrm{H}^{+}\right]_{\text {todal }} \approx\left[\mathrm{H}^{+}\right]_{\mathrm{A}}$
and from I equilibrium, $\left[\mathrm{H}^{+}\right]_{\mathrm{A}} \approx\left[\mathrm{HCO}_3^{-}\right] \approx\left[\mathrm{H}^{+}\right]_{\text {tocal }}$
$\left[\mathrm{CO}_3^{-2}\right]$ is negligible compared to $\left[\mathrm{HCO}_3^{-}\right]$or $\left[\mathrm{H}^{+}\right]_{\text {total }}$
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