[anastasiaaleexev]

1. Adding NaNO₃ to a HNO₃ solution
2. Adding NaCN to a HCN solution
3. Adding NaOH to a NH₃ solution

I said that all 3 will increase in pH. Is that correct?

[chenbeier]

No.1 I would think again. No.2 is also questionable, regarding built up of a buffer.
No.3 is correct.

[anastasiaaleexev]

My thinking was that when you add NaNO₃ and the NaCN, you will be increasing the concentration of the products (NO₃^- and CN^-), so the equilibrium will shift to the reactants, causing [H⁺] to decrease.

Since this is incorrect, what would be the explanation for it?

[Borek]

A lot depends on how much detailed answer you are seeking, you asked in a High School forum, so I assume HS level.

In the case of a strong acid adding salt doesn't matter at all - it is still fully dissociated and (assuming there were no volume/concentration changes) pH doesn't change. In reality it is a bit more complicated.

You are right with 2. though, yes, presence of CN^- will shift the dissociation and the pH will go up.

3. is OK as well.

[anastasiaaleexev]

Got it, thank you!