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How many grams of NAC2H3O2 must be dissolve in enough water to prepare 250.0 mL of a solution with a pH= 9.200? Molar mass of NaC2H3O2 ia 82.03 g/mol. Ka for C2H3O2H is 1.8x10^-5

  • chemistry -

    If we call acetic acid HAc, then the pH will be determined by the hydrolysis of the salt. Convert pH 9.200 to OH^-. I get about 1.6E-5M
    ..............Ac^- + HOH -->HAc + OH^-
    initial......x..............0.....0
    equil......x-1.6E-5.......1.5E-5..1.6E-5

    Kb = (Kw/Ka) = (HAc)(OH^-)/(Ac^-)
    Substitute and solve for Ac^-,(answer will be in moles/L) and multiply that by 0.250 to find moles in 250 mL, then
    that x molar mass NaAc give grams NaAc in 250 mL.

  • chemistry -

    omg, thank u! I ended up getting something 1.70! THANKS!

  • chemistry--corr'n -

    Where I wrote 1.6E-5 for concn OH^-, I should have typed 1.6E-5 ALSO for (HAc) but I made a typo with 1.5E-5. By the way,
    I think the answer is closer to 9 g. Post your work if you wish and I will look for the error.

  • chemistry -

    I actually just redid it and found something close to 9.21?

  • chemistry -

    Right. My answer was 9.22 g.

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