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What is an expression for the acid ionization constant (#K_a#) for #H_2CO_3#?

Answer 1

#K_a=([H_3O^+][HCO_3^(-)])/([H_2CO_3])#

Additionally, the reaction is represented by this equilibrium expression.

#H_2CO_3(aq) +H_2O(l)rightleftharpoonsH_3O^+ + HCO_3^(-)#

Note that the existence of carbonic acid in aqueous solution may be a bit fanciful....the species in solution is likely...#H_2O*CO_2-=H_2CO_3#..i.e. carbon dioxide solvated by water. You are on your own with finding #K_a#...it is small.

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Answer 2

Naomi Aronson

[ K_a = \frac{[\text{HCO}_3^-][\text{H}^+]}{[\text{H}_2\text{CO}_3]} ]

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.