If you have 500 ml of .15M Formic Acid, what is the pH of this solution? What is the

Question

pKa? How many grams of Sodium Formate would you have to add to raise the pH to 3.85? How many grams of HCl would you have to add to lower the new pH by .2 ?

Answer 1

I'll get you started. It appears to me you've just copied the problem and haven't tried anything. Look up Ka for formic acid. pka = -log Ka.

Let HFo stand for formic acid.
Then .......................HFo ==> H^+ + Fo^-
I................................0.15.......0..........0
C................................-x.........x...........x
E...........................0.15-x........x...........x
Write the expression for Ka, substitute the E line into the Ka expresion and solve for x = (H^+), then convert to pH.

grams of HCOONa needed to raise pH to 3.85 is done with the Henderson-Hasselbalch equation. Same for grams HCl to change pH from 3.85 to 3.65.
Post your work if you get stuck.