Chemistry

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An unknown monoprotic weak acid, HA, has a molar mass of 65.0. A solution contains 2.20 g of HA dissolved 750. mL of solution. The solution has a pH of 2.200. What is the value of Ka for HA?

  • Chemistry -

    HA ==> H^+ + A^-

    (H^+)(A^-)/(HA) = Ka
    moles HA = moles/molar mass = 2.20/65 = 0.0338
    (HA) = (0.0338/0.750) = 0.0451 M
    pH = 2.200
    2.200 = -log(H^+)
    (H^+) = 0.00631
    Substitute into Ka expression.
    (0.00631)(0.00631)/(0.0451-0.00631) = Ka.
    You can finish.

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