How much would you have to add

Question

Phosphoric acid is a commonly used biological buffer because the pKa for dissociation of its second proton is near neutral pH(7.21). The following questions relate to a 100 mL solution containing 50 mM KH2PO4, prepared from solid KH2PO4 in water.

a) Do you expect the initial pH of the solution to be higher or lower than 7.21? Why?

b) At pH 7.35, what is the ratio ofH₂PO₄^-/HPO₄^2-?

c) To bring the solution to a pH of 7.35 , how much 0.100 M KOH or0.100 M HCl (assume 100% dissociation for either) would youhave to add if the initial pH of the solution was 5.36? How much would you have to add if the initial pH was 9.26?