Calculate the carbonate ion concentration in a 0.10 M solution of the weak acid, carbonic acid are (H2CO3).

Home / Question Answer / Calculate the carbonate ion concentration in a 0.10 M solution of the weak acid, carbonic acid are (H2CO3).

The dissociation constants of carbonic acid are

K_a1 = 4.5 x 10^-7 and K_a2 = 4.7 x 10^-11 .

(a) 4.7 x 10^-11 M

(b) 1.0 x 10^-7 M

(c) 4.5 x 10^-7 M

(d) 2.1 x 10^-4M

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H₂CO₃ ⇌ HCO₃^- + H⁺ (K_a1)

HCO₃^- ⇌ CO₃^2- + H⁺ (K_a2)

c=0.10M

Most will be from Ka,

α=√ K_a1 / C

√4.5×10^-7 / 1×10^-2

√4.5×10^-5

=6.70 ×10-2

= .067 = .067 < .1

∴[H⁺ ]=cα

=0.10 × 0.067

=.0067

[H⁺][HCO3^- ] / [H₂CO₃ ] =Ka,

⇒ .0067 ×[HCO₃^-] / 0.10 = 4.5×10^-7

⇒[HCO₃^-] = 4.5×10-7/ .0067 × 0.10

=0.671 × 10^-3

Final answer: The correct answer will be 0.671 × 10^-3.

solved 5

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