Salts as Acids and Bases

[Milind_Vasudev_2H]

How do we know if certain anions affect the pH of a solution or not. In the course reader, for a solution containing NH4+ and Cl- it says that Cl- doesn't affect the pH, but how do we know this?

[Alexandra_Ivanova_1A]

I think it has more to do with what is actually reacting. In the example you are using, we are looking at NH₄Cl. This is a salt that contains an acid within it (NH₄). The acid is what is reacting with water, not the anion (Cl^-). Since Cl^- isn't reacting, it doesn't affect the pH. This is further seen in that if you wanted to include it in the written reaction, you would need to add it to both sides-- cancelling it out. For the anion to affect the pH it would need to actually be an acid or base. For instance. HSO4^- is an anion, but it is also an acid. My way of looking at it, is that Cl^- on its own isn't really an acid or base, so it wouldn't affect the pH.