Question
A 0.942 M sample of carbonic acid, H2CO3, has a measured hydronium ion concentration of 6.36 ´ 10–4 M. Calculate the acid-ionization constant of carbonic acid. The equilibrium equation is:
H2CO3(aq) + H2O(l) <--><--> H3O+(aq) + HCO-3(aq)
H2CO3(aq) + H2O(l) <--><--> H3O+(aq) + HCO-3(aq)
Answers
Ka = (H3O^+)(HCO3^-)(H2CO3)
Set up an ICE chart, substitute into Ka expression, and solve for Ka.
Post your work if you get stuck.
Set up an ICE chart, substitute into Ka expression, and solve for Ka.
Post your work if you get stuck.
what is an ICE chart?
ICE.
I = initial
C = change
E = equilibrium.
H2CO3 + H2O ==> H3O^+ + HCO3^-
Ka = (H3O^+)(HCO3^-)/(H2CO3).
initial:
H2CO3 = 0.942 M
(H3O^+) = 0
(HCO3^-) = 0
equilibrium:
(H3O^+) = 6.36 x 10^-4 M
(HCO3^-) = 6.36 x 10^-4 M
(H2CO3) = 0.942-6.36 x 10^-4 = 0.942
This solution assumes Ka is the only ionization constant for H2CO3; in reality, H2CO3 has a k1 and a k2 but we are ignoring k2. The error is small.
I = initial
C = change
E = equilibrium.
H2CO3 + H2O ==> H3O^+ + HCO3^-
Ka = (H3O^+)(HCO3^-)/(H2CO3).
initial:
H2CO3 = 0.942 M
(H3O^+) = 0
(HCO3^-) = 0
equilibrium:
(H3O^+) = 6.36 x 10^-4 M
(HCO3^-) = 6.36 x 10^-4 M
(H2CO3) = 0.942-6.36 x 10^-4 = 0.942
This solution assumes Ka is the only ionization constant for H2CO3; in reality, H2CO3 has a k1 and a k2 but we are ignoring k2. The error is small.
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