Problem: HF is a weak acid with Ka = 7.2 x 10-4What is the value of the equilibrium constant for the reaction:HF(aq) + OH-(aq) ⇌ H2O(λ) + F-(aq)A. 7.2 x 10-4B. 1.4 x 10-11C. 1.4 x 105D. 2.4 x 10-5E. 7.2 x 1010

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We're being asked to write the equilibrium constant  for the following reaction: 

HF(aq) + OH-(aq) ⇌ H2O(l) + F-(aq)


To determine the equilibrium constant, K, of the reaction equation, we’re going to use Hess’s Law. We’re going to manipulate some reactions with given K value to get the reaction equation with the unknown K

Recall the autoionization of water at 25°C:

H2O(l) ⇌ H+(aq) + OH-(aq)          Kw = 1.0x10-14

HF is a weak acid and it will partially dissociate in the solution:

HF ⇌ H+(aq) + F-(aq)                   Ka = 7.2x10-4

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Problem Details

HF is a weak acid with Ka = 7.2 x 10-4

What is the value of the equilibrium constant for the reaction:

HF(aq) + OH-(aq) ⇌ H2O(λ) + F-(aq)

A. 7.2 x 10-4

B. 1.4 x 10-11

C. 1.4 x 105

D. 2.4 x 10-5

E. 7.2 x 1010

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