Question

What is the pH change of a 0.220M solution of citric acid (pKa=4.77) if citrate is added to a concentration of 0.155M with no change in volume?

Answer 1

pKa = 4.77 is pK2; therefore, I assume you are asking for the change in pH of that solution, not necessarily that of citric acid. Use the HH equation.

Answer 2

I tried the HH equation and got pH=4.92 when I placed the acid on top of the fraction and that was wrong. I got 4.61 when I placed the citrate on top and that was also wrong...