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Question

# In aqueous solution the ionization constants for carbonic acid are K1=4.2×10−7 and K2=4.8×10−11 Select the correct statement for a saturated 0.04 M solution of the carbonic acid

A
The concentration of CO23 0.034 M.
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B
The concentration of CO23 is greater than that of HCO3
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C
The concentrataion of H+ and HCO3 are approximately equal.
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D
The concentration of H+ is double that of CO23
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Solution

## The correct option is C The concentrataion of H+ and HCO−3 are approximately equal.A→H2CO3(aq.)⇌H+(aq.)+HCO−3(aq.) K1=4.2×10−7B→HCO−3(aq.)⇌H+(aq.)+CO2−3(aq.) K2=4.8×10−11As,K2<<K1. So, all major part of [H+] comes from dissociation of H2CO3. [H+]total≈[H+]A and from first equilibrium. [H+]A≈[HCO−3]≈[H+]total [CO−23] is negligible compared to [HCO−3] or [H+]total Theory : Ka for weak acids For the following reaction : HA(aq) + H2O(l)⇌H3O+(aq)+A−(aq) Ka=[H3O+][A−][HA] Kb for weak bases For the following reaction : MOH(aq) + H2O(l)⇌M+(aq)+OH−(aq) Kb=[M+][OH−][MOH] Note : More the values of Ka or Kb more is the strength of acid or base

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