Question

Hey guys! Trying to understand this problem before my Chem exam but I just can't get it down no matter how hard I try.

Detailed solutions would be greatly appreciated because I'm so lost on this one.

Thanks!


What mass of ammonium chloride must be added to 5.00x10^2 mL of 0.10 M NH3 solution to give a solution with pH=9.0. pKa=9.24

Answer 1

Use the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid)
9.0 = 9.24 + log 0.1M/(acid)
Solve for (acid) in M.
Then M = mols/L.
You know M and L, solve for mols.
Then mol = grams/molar mass. You know mol and molar mass, solve for grams. Piece of cake.