Adding a few drops of 1M NH4Cl to 0.1M NH4OH increased NH4+, lowered OH-. what if more some 6M NH4OH is added?

Question

the experiment was adding 1M NH4Cl to a 0.1M NH4OH soln which had phenolphthalein indicator in it. The solution went from pink to colorless, indicating that [NH4+] went up, [OH-] decreased.

then, we added some concentrated 6M NH4OH, which ions' concentration are added to the equilibirum? both [Nh4+] and [OH-]? and how does the change in [OH-] affect [H3O+]?

Thank you!

Answer 1

I don't like the formula NH4OH, because basically the substance doesn't exist.

You have been studying the equilibrium NH3 + H2O <-----> (NH4)+ + OH-.

You found that adding extra (NH4)+ ions decreased the concentration of OH- ions, showing that the equilibrium had shifted to the left.

Adding concentrated ammonia solution (6M, which is almost entirely NH3) will cause the equilbrium to move to the right, increasing the concentration of OH- ions. There are hardly any ammonium and hydroxide ions in concentrated ammonia solution.

OH- ions and (H3O)+ ions go up and down in concentration in a strict relationship of inverse proportionality.