Posted by PLEASE HELP! on Monday, October 3, 2011 at 9:42pm.
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 - DrBob222, Monday, October 3, 2011 at 10:23pm
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^-
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 - PLEASE HELP!, Monday, October 3, 2011 at 10:53pm
omg, thank u! I ended up getting something 1.70! THANKS!
chemistry--corr'n - DrBob222, Monday, October 3, 2011 at 11:24pm
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 - PLEASE HELP!, Tuesday, October 4, 2011 at 12:57am
I actually just redid it and found something close to 9.21?
chemistry - DrBob222, Tuesday, October 4, 2011 at 11:33am
Right. My answer was 9.22 g.
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