- #1

Mholnic-

- 43

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## Homework Statement

A particular sample of vinegar has a pH of 2.90. If acetic acid is the only acid that vinegar contains (Ka = 1.8 x 10

^{-5}), calculate the concentration of acetic acid in the vinegar.

## Homework Equations

Ka = [Products]/[Reactants]

pH = -log[H

^{+}]

## The Attempt at a Solution

I arranged the problem in my usual lazy way:

Acid + Water ---> Conjugate Base + Hydrogen Ions

Assuming that [H

^{+}] is equal to [Conjugate Base] I calculated the concentration of the conjugate base and hydrogen ions.

pH = -log[H

^{+}] = 2.90

[H

^{+}] = 10

^{-2.90}= [Conjugate Base]

Then I plugged those numbers and the given Ka value into:

Ka = [products]/[reactants]

1.8 x 10

^{-5}= [10

^{-2.90}]

^{2}/[Acid]

[10

^{-2.90}]

^{2}/1.8 x 10

^{-5}= [Acid]

I get 8.8 x 10

^{-12}. The book says the answer is .089 M. Not quite sure where I'm going wrong.. maybe I am not using the correct equations or perhaps it's an overlooked error in algebra. Help!