I made two similar ammonia solutions in different ways, and they resulted in different pH, but i'm not sure why.
Added 5.84 g NaCl to a 500 mL flask. Then added 10 mL 25% ammonia solution. Filled to 500 mL with distilled water to make a 500 mL 0.5% ammonia solution (0.267 M) with 0.2 M NaCl.
NH3 + H2O + NaCl --> NH4 (but mostly NH3) + OH- (but mostly H2O) + Na + Cl-
Added 14.8504 g NH4Cl to 722 mL distilled water. Added 278 mL 1 M NaOH. This leaves me with a 1 L solution of 0.5% ammonia (0.278 M) and 0.278 M NaCl
~ NH4Cl solution~
NH4Cl + H2O --> NH4 + Cl (pH.5?)
NH4 + Cl + H2O --> NH3 + H3O+ + Cl (pH 5?)
NaOH + H2O --> Na + OH- (pH 10)
~Adding NaOH to NH4Cl solution~
Na + OH- + NH3 + H3O+ + Cl --> NaCl + NH3 + H2O
Both solutions contain roughly similar the molar amount of ammonia (~0.2 M) and NaCl, and should result in a final composition of NaCl + NH3 + H2O. Yet, the pH of the solutions greatly differ.
Is it that in solution 2, ammonia is existing mainly as NH4, or perhaps there are remaining hydronium ions?
Any advice would be appreciated.