The pH of a 0.020 mol/L solution of H2S(aq) is?

1 Answer

Relevance
  • 12 months ago
    Favorite Answer

    What is the pH.......

    Assume H2S is a monoprotic acid. The ionization of HS- is negligible. Suflide ions are only found in extremely basic solutions (an excess of OH- ions).

    H2S(aq) <==> H+ + HS- ................. Ka = 9.5x10^-8

    0.020M ...........0 .......0 .................... initial

    -x ................... +x .... +x .................. change

    0.020-x ........... x ...... x ................... equilibrium

    Ka = [H+][HS-] / [H2S]

    9.5x10^-8 = x^2 / (0.020-x) ............. assume 0.02-x = 0.2 since x will be small

    x = 4.4x10^-5

    [H+] = 4.4x10^-5M

    pH = -log[H+] = 4.36 .......... to two significant digits

    When taking the log of a number, only the digits to the right of the decimal reflect the precision in the original number.

    ===============

    The answer is accurate. Don't be put off by the "thumbs down." It's the work of a troll.

    Hmmmm? Is the troll just being a troll, or is the troll put off by the fact that H2S acts as a monoprotic weak acid? If the troll has a concern then he should speak up.

Still have questions? Get your answers by asking now.