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3 November, 20:57

What is the pH of 0.10 M NaF (aq). The Ka of HF is 6.8 x 10-4

2.08

8.08

5.92

14.92

+2
Answers (1)
  1. 3 November, 21:14
    0
    Given information:

    Concentration of NaF = 0.10 M

    Ka of HF = 6.8*10⁻⁴

    To determine:

    pH of 0.1 M NaF

    Explanation:

    NaF (aq) ↔ Na + (aq) + F - (aq)

    [Na+] = [F-] = 0.10 M

    F - will then react with water in the solution as follows:

    F - + H2O ↔ HF + OH-

    Kb = [OH-][HF]/[F-]

    Kw/Ka = [OH-][HF]/[F-]

    At equilibrium: [OH-]=[HF] = x and [F-] = 0.1 - x

    10⁻¹⁴/6.8*10⁻⁴ = x²/0.1-x

    x = [OH-] = 1.21*10⁻⁶ M

    pOH = - log[OH-] = - log[1.21*10⁻⁶] = 5.92

    pH = 14 - pOH = 14-5.92 = 8.08

    Ans: (b)

    pH of 0.10 M NaF is 8.08
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