Question

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

Answer 1

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.

Answer 2

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

Answer 3

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.

Answer 4

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

Answer 5

Right. My answer was 9.22 g.