How to tell if salt affects pH

[006058674]

Hi!
I am wondering how to tell when a dissolved salt affects pH. In an example in class, Dr. Lavelle mentioned that the potassium in potassium nitrate doesn't change the pH, so we don't need to include it in the equilibrium. How do we know which elements do affect the pH and which don't?

Thank you!

[Anita Sarransingh 2A]

Hi! I think most elements in columns 1 and 2 of the periodic table cannot affect pH since they only make +1 and +2 charges, and this is not strong enough to have an impact on the water it is dissolved in. Magnesium can have a slight acidic effect on pH, but this is an exception. Some of the transition metals that can form +3 and +4 charges, such as iron or aluminum, can have an acidic effect on pH since they have these more strongly positive charges, which are attracted to the oxygen in water and increase the concentration of free H+.

[Angela Yang 2J]

I think another consideration is whether the cation or anion reacts with water in the first place. ie. table salt has no effect on pH since its cation and anion do not react with water. On the other hand something like NH4Cl in water produces the NH4+ ion which reacts to produce hydronium ions, thus turning the solution acidic.

[Emmet Asker]

Given that some transition metals can affect pH but metals in groups 1 and 2 do not, how do we determine which transition metals affect pH and when they do? For example, Lead can have a +2 charge or a +4 charge. How would we decide whether it will affect the pH in a given situation?

[KWilson_Disc_2F]

I think another consideration is whether the cation or anion reacts with water in the first place. ie. table salt has no effect on pH since its cation and anion do not react with water. On the other hand something like NH4Cl in water produces the NH4+ ion which reacts to produce hydronium ions, thus turning the solution acidic.

What would be the best way to tell if the cation/anion is going to react fully with water? Would it just be if the product/reactants are aqueous?