A particular sample of vinegar has a pH of 2.9. Assuming that the acetic acid is the only acid that the vinegar contains (Ka= 1.8x10^-5), calculate the concentration of the acetic acid.
Answer:
The equilibrium is :
CH3COOH <> CH3COO- + H+
If pH = 2.9
[H+] = 10^-2.9 = 0.00126 M
At equlibrium
[H+] = [ CH3COO-] = 0.00126 M
[CH3COOH ] = x - 0.00126
Ka = 1.8 x 10^-5 = (0.00126)^2 / x - 0.00126
x = 0.088 M This is initial concentration of acetic acid.
at equilibrium [CH3COOH] = 0.088 - 0.00126 = 0.087 M
2.68 %
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