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16 September, 00:54

A solution of ammonia has a pH of 10.50. what is the initial molarity of ammonia? Kb for ammonia is 1.8x10^-5

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  1. 16 September, 01:08
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    5.55 x 10⁻³ mol/L.

    Explanation:

    ∵ pH + pOH = 14.

    ∴ pOH = 14 - pH = 14 - 10.50 = 3.5.

    ∵ pOH = - log[OH⁻].

    ∴ - log[OH⁻] = - 3.5.

    ∴ [OH⁻] = 3.16 X 10⁻⁴.

    ∵ [OH⁻] = √ (kb) (c)

    kb = 1.8 x 10⁻⁵.

    c is the initial concentration.

    3.16 X 10⁻⁴ = √ (1.8 x 10⁻⁵) (c).

    by squaring both sides:

    (3.16 X 10⁻⁴) ² = (1.8 x 10⁻⁵) (c).

    1.0 x 10⁻⁷ = (1.8 x 10⁻⁵) (c)

    ∴ c = (1.0 x 10⁻⁷) / (1.8 x 10⁻⁵) = 5.55 x 10⁻³ mol/L.
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