The K_a of acetic acid (HC₂H₃O₂)is 1.8 × 10^-5. What is the pH at 25.0 °C of an aqueous solution that is 0.100 M in acetic acid?

Question

Quizplus · Accepted Answer

The equation to calculate the pH of a weak acid solution is pH=pKa+log([A-]/[HA]).
Where: 
pKa = 4.76 (from the given value of Ka=1.8 × 10^-5)
[A-]/[HA] = 1.8/0.1 = 18
Substituting the values in the equation above gives pH = 4.76 + log(18) = 2.87.
Note that the negative logarithm of a number between 0 and 1 is a positive number.

The Ka of Acetic Acid (HC2H3O2)is 1

The K_a of Acetic Acid (HC₂H₃O₂)is 1