Ions as Bases/Acids

[Stacey Phan 2I]

Can someone explain how to determine when an ion is basic or acidic?

[JonathanSung_2G]

In terms of looking at salts, you can tell which salts will behave as acids or bases. For example, NH4+ Cl- + H2O -> NH3 + H3O+ Cl-, chlorine does not affect the pH which means it has no effect as an acid or base. However, H3O+ concentration increases, which lowers the pH. You will need to see which ions can donate H+ or accept an H+, and this will help you determine whether the solution is basic or acidic. You'll also need to determine the ions that affect the pH and the ones that don't. We typically memorize the metal cations that increase H3O+ when hydrated (Fe3+, Cr3+, Al3+, and Fe2+) which are considered Lewis Acids, and the ions that behave as Lewis Bases when hydrated (CO3 2-, PO4 3-, OH-, F-, O2-, S2-). Hope this helped!

[Stacey Phan 2I]

In terms of looking at salts, you can tell which salts will behave as acids or bases. For example, NH4+ Cl- + H2O -> NH3 + H3O+ Cl-, chlorine does not affect the pH which means it has no effect as an acid or base. However, H3O+ concentration increases, which lowers the pH. You will need to see which ions can donate H+ or accept an H+, and this will help you determine whether the solution is basic or acidic. You'll also need to determine the ions that affect the pH and the ones that don't. We typically memorize the metal cations that increase H3O+ when hydrated (Fe3+, Cr3+, Al3+, and Fe2+) which are considered Lewis Acids, and the ions that behave as Lewis Bases when hydrated (CO3 2-, PO4 3-, OH-, F-, O2-, S2-). Hope this helped!

Why does chlorine not affect the pH? Is it because when combined with H, HCl is a strong acid that dissociates?

[Crystal Pan 2G]

In terms of looking at salts, you can tell which salts will behave as acids or bases. For example, NH4+ Cl- + H2O -> NH3 + H3O+ Cl-, chlorine does not affect the pH which means it has no effect as an acid or base. However, H3O+ concentration increases, which lowers the pH. You will need to see which ions can donate H+ or accept an H+, and this will help you determine whether the solution is basic or acidic. You'll also need to determine the ions that affect the pH and the ones that don't. We typically memorize the metal cations that increase H3O+ when hydrated (Fe3+, Cr3+, Al3+, and Fe2+) which are considered Lewis Acids, and the ions that behave as Lewis Bases when hydrated (CO3 2-, PO4 3-, OH-, F-, O2-, S2-). Hope this helped!

Why does chlorine not affect the pH? Is it because when combined with H, HCl is a strong acid that dissociates?

Small highly charged anions/cations will have an effect on the pH. Typically you will need a more highly charged cation (in most cases) to act as the lewis acid.