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JEE Main 2010
Exam
JEE Main
Year
2010
Subject
Chemistry
Chapter
Chemical Equilibrium

JEE Main 2010 · Chemistry · Chemical Equilibrium

In aqueous solution the ionization constants for carbonic acid are...

In aqueous solution the ionization constants for carbonic acid are K1=4.2×10−7\mathrm{K}_1=4.2 \times 10^{-7} and K2=4.8×10−11\mathrm{K}_2=4.8 \times 10^{-11} Select the correct statement for a saturated 0.034M0.034 \mathrm{M} solution of the carbonic acid.

Options

  1. AThe concentration of CO32−\mathrm{CO}_3^{2-} is 0.034M0.034 \mathrm{M}.
  2. BThe concentration of CO32−\mathrm{CO}_3^{2-} is greater than that of HCO3−\mathrm{HCO}_3^{-}.
  3. CThe concentration of H+\mathrm{H}^{+}and HCO3−\mathrm{HCO}_3^{-}are approximately equal.
  4. DThe concentration of H+\mathrm{H}^{+}is double that of CO32−\mathrm{CO}_3^{2-}.

Correct answer

C. The concentration of H+\mathrm{H}^{+}and HCO3−\mathrm{HCO}_3^{-}are approximately equal.

Step-by-step solution

A→H2CO3⇌H++HCO3−K1=4.2×10−7 B→HCO3−⇌H++CO3−2 K2=4.8×10−11\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 K2≪K1\mathrm{K}_2 \ll \mathrm{K}_1 All major [H+]todal ≈[H+]A\left[\mathrm{H}^{+}\right]_{\text{todal }} \approx\left[\mathrm{H}^{+}\right]_{\mathrm{A}} and from I equilibrium, [H+]A≈[HCO3−]≈[H+]tocal \left[\mathrm{H}^{+}\right]_{\mathrm{A}} \approx\left[\mathrm{HCO}_3^{-}\right] \approx\left[\mathrm{H}^{+}\right]_{\text{tocal }} [CO3−2]\left[\mathrm{CO}_3^{-2}\right] is negligible compared to \left[\mathrm{HCO}_3^{-}\right]or[H+]total or \left[\mathrm{H}^{+}\right]_{\text{total }}
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