When 50.0mL of 0.100M NH3 (Kb=1.8x10^-5) solution is mixed with 20.0mL of of 0.250M HCl solution, what is the pH after reaction?

I solved the ka=5.56x10^-10 and I solved the moles of each nHCl and nNH3 and both have 0.005 moles. What do I do after this?

1 answer

If the reaction is mole for mole, then y0u have the salt at the end of the reaction. Hydrolyze the salt (react it with water) and go from there.
NH4Cl ==> NH4^+ | Cl^-
The NH4^+ hydrolyzes.
NH4^+ + HOH ==> NH3 + H3O^+
Set up and ICE chart and solve for H3O^+ and from there you can get pH.