Chemistry
posted by Bella .
A solution is prepared by dissolving 50.0 g of pure HC2H3O2 and 20.0 g of NaC2H3O2 in 975 mL of solution (the final volume).
what is the ph?
What would the pH of the solution be if 50.0 mL of 0.900 M NaOH were added?
What would the pH be if 30.0 mL of 0.30 M HCl were added to the original 975 mL of buffer solution?
Please help I have tried using the Henderson Hasselbach equation and I am not getting the correct answer.

Show your work and I'll guide you through it.
First, just the pH of the solution. 
I multiplied 50g by 975 mL and then 20g by 975 mL. Then I used the given pKa of 4.745 + log (19,500 / 48,750) = 4.35

Thos are molarities that go in the HH equation.
mols HAc = 50/molar mass HAc
M HAc = mols/0.975L = ?
mols NaAc = 20/molar mass NaAc.
M NaAc = mols/0.975
pH = pKa + log b/a
I get close to 4.2 but that approximate.
By the way you can take a shortcut and use mols base/mols acid and obtain the same answer as if you used M base/M acid. That's because the 975 mL cancels.