Question

1) Solution Components

A 1 mL 100 mM NaH2PO4 + 9 mL 100 mM Na2HPO4

B 5 mL 100 mM NaH2PO4 + 5 mL 100 mM Na2HPO4

C 9 mL 100 mM NaH2PO4 + 1 mL 100 mM Na2HPO4

D 10 mL 100 mM NaH2PO4 stock solution

E 10 mL 100 mM Na2HPO4 stock solution

F 10 mL distilled water

pKa of phosphate: 6.8

How would you calculate the pH of each equation using the Henderson Hasselbalch equations?

2) Tris buffer (pKa 8.3) is a weak organic base. It’s available in solid form as “Tris base” (MW =
121.1 g/mol) and “Tris acid” (MW = 157.6 g/mol).

Calculate the theoretical pH of a solution that contains 80 mL of 50 mM Tris base and 20 mL of the 50 mM Tris acid. (my answer = 10.4) At what pH will the acid and base forms of Tris be present at the same concentrations?

My answer was 8.3 but I'm not sure if that's right.

Answer 1

2) # Theoretical pH value is 8.78 for the solution containing 80 mL of 50 mM Tris base and 20 mL of the 50 mM Tris acis.

## At pH 8.3 the acid and base forms of Tris will be present at the same concentrations.