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Acetic acid is a weak acid with the formula , CH3COOH, the Ka for acetic acid is 1.76 x 10-5.

In aqueous solution, acetic acid partially dissociates according to the following reaction:

CH3COOH ⇔ CH3COO- + H+

Use the Ka equation to calculate the pH of the acetic acid solution described below:
Volume: 350 mL
Concentration: 0.2853 M

Since this is a weak acid, you can assume the amount of acid dissociated is << 5% of the total amount of acid present.

Report your answer with the correct number of significant digits.

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1 answer
  1. Let's say CH3COOH = HAc
    ...........HAc ==> H^+ + Ac^-
    I........0.2853........0.........0
    C........-x...............x..........x
    E......0.2853-x.......x..........x

    Substitute the E line into the Ka expression and solve for x = (H^+) and convert that to pH. pH= -log(H^+)
    Note that it's a little ridiculous to have a concn of 0.2853 when the Ka value is not know to that accuracy.
    Post your work if you get stuck.

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    DrBob222

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