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    I am doing my assignment and I am stuck with these questions:
    1. Calculate the pH of a buffer solution containing 0.15 mol dm-3 methanoic acid, HCOOH(aq) and 0.065 mol dm-3 sodium methanoate, HCOONa(aq), at 25oC. Ka of HCOOH = 1.6 x 10-4 mol dm-3 at 25oC.

    2. Calculate the pH at 25oC of a buffer solution containing 0.050moldm-3 CH3COOH(aq) and 0.10mol dm-3 CH3COO-Na+(aq); CH3COOH, Ka = 1.7 x 10-5 moldm-3.

    I get for the:
    Q1: pH = 3.43 (or 3.44)
    Q2: pH = 4.74 (or 5.07)

    I would appriciate any help possible thank you

    Remember that for a buffer:
    concentration of H+ = (Ka x concentration of HA)/concentration of A- where HA is the acid and A- is the salt
    1. H+ = (1.6x10^-4 x 0.15)/0.065
    H+ = 3.69x10^-4 (3sf)
    pH = -log(H+)
    pH = -log(3.69x10^-4)
    pH = 3.43
    2. H+ = (1.7x10^-5 x 0.050)/0.10
    H+ = 8.5x10^-6
    pH = -log(H+)
    pH = -log(8.5x10^-6)
    pH = 5.07

    Hopefully this helps
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