Atomic StructureHard

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 0.034 M solution of the carbonic acid.

Options

A.The concentration of CO32- is 0.034 M.
B.The concentration of CO32- is greater than that of HCO3-.
C.The concentration of H+ and HCO3-  are approximately equal.
D.The concentration of H+ is double that of CO32-.

Solution

A →      H2CO3 ⇋ H+ + HCO3-     K1 = 4.2 × 10-7
B →      HCO3- ⇋ H+ + CO3-2       K2 = 4.8 × 10-11
As K2 ≪ K1
All major [H+]total [H+]A
and from I equilibrium, [H+]A [HCO3-] [H+]total
[CO3-2] is negligible compared to [HCO3-] or [H+]total

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