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6 January, 04:55

The first disinfectant used by Joseph Lister was called carbolic acid. This substance now is known as phenol, C6H5OH (pKa = 9.90). What is the pH of a 0.10 M solution of phenol?

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  1. 6 January, 06:23
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    5.5

    Explanation:

    Phenol is a weak acid that dissociates according to the following reaction.

    C₆H₅OH (aq) ⇄ C₆H₅O⁻ (aq) + H⁺ (aq)

    The pKa is 9.90. The acid dissociation constant (Ka) is:

    pKa = - log Ka

    Ka = antilog - pKa = antilog - 9.90

    Ka = 1.26 * 10⁻¹⁰

    Given the concentration of the acid, Ca = 0.10 M, and the Ka, We can find [H⁺] using the following expression.

    [H⁺] = √ (Ka * Ca)

    [H⁺] = √ (1.26 * 10⁻¹⁰ * 0.10)

    [H⁺] = 3.5 * 10⁻⁶ M

    The pH is:

    pH = - log [H⁺]

    pH = - log 3.5 * 10⁻⁶

    pH = 5.5
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