For 520.0mL of a buffer solution that is 0.140M in HC2H3O2 and 0.125M in NaC2H3O2, calculate the initial pH and the final pH after adding 0.020mol of HCl

Answer 1

millimols HAc = mL x M = ? = acid
mmols NaAc = mL x M = ? = base.

Plug these into the Henderson-Hasselbalch equation and solve for pH.

part 2. mmols HCl added = 20
I will make up some numbers for mmols HAc and NaAc to make this easier to do but these aren't real numbers. You must go through the calculations above and use those numbers.
...........Ac^- + H^+ ==> HAc
I...........65....0.......75
add..............20...........
C..........-20..-20.......+20
E...........45....0........95

Plug these new E line numbers (after you have the REAL numbers that go there) into the HH equation and solve for the new pH.

Answer 2

How many grams of iron(III) sulfide form when 62.0 mL of
0.135 M iron(III) chloride reacts with 45.0 mL of 0.285 M calcium
sulfide?