How many grams (to the nearest 0.01 g) of NH4Cl (Mm = 53.49 g/mol) must be added to 700. mL of 1.294-M solution of NH3 in order to prepare a pH = 9.70 buffer? (pka of NH3 = 9.25)

Answer 1

Use the Henderson-Hasselbalch equation.
pH = pKa + log [(base)/(acid)]
You have pH, pKa, and molarity of the base. Solve for (acid) [which in this case is the NH4Cl).
Knowing (acid), calculate grams needed to make 700 mL of that concentration.