chemistry
posted by PLEASE HELP! on .
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

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 1.6E5M
..............Ac^ + HOH >HAc + OH^
initial......x..............0.....0
equil......x1.6E5.......1.5E5..1.6E5
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. 
omg, thank u! I ended up getting something 1.70! THANKS!

Where I wrote 1.6E5 for concn OH^, I should have typed 1.6E5 ALSO for (HAc) but I made a typo with 1.5E5. 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. 
I actually just redid it and found something close to 9.21?

Right. My answer was 9.22 g.