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John Arcadia
John Arcadia asked in Science & MathematicsChemistry · 6 years ago

Chemistry homework help: Acids, Bases, and pH?

A solution of formic acid is found to have a pH of 2.0. What is the molarity of the solution of formic acid (Ka = 1.78 x 10-4)

H(CHO2) <-----> H+ + CHO2-

Please show me all the steps required to answer this question. I have to solve other questions like this.

2 Answers

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  • Simonizer1218
    Lv 7
    6 years ago

    H(CHO2) --->H+ + CHO2-

    Ka = [H+][CHO2-]/[[H(CHO2]

    From pH = -log[H+] you can calculate [H+] = 1x10^-2. This will also be [CHO2-]. Thus...

    1.78x10^-4 = (1x10^-2)(1x10^-2)/x

    x = 1x10^-4/1.78x10^^-4

    x = 0.562 M

    NOTE: This is the same answer as posted by Jan, however, I'm hoping you can follow this reasoning. If you can follow the calculations of the previous answer, more power to you. Not exactly intuitive.

  • Jan
    Lv 7
    6 years ago

    pH = 2 = 0.5(pKa - lg(HA))

    lg(HA) = -025

    HA = 0.562 M

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