Classifying Salts

[Ziyi Meng 2K]

Hi,

Can someone help me review how to classify salts as acidic, basic, or neutral?

[Bryan Cheng 1H]

To classify salts, you need to look at the components that make them up (the ions). Remember the conjugate seesaw -- the stronger the acid/base, the weaker the conjugate base/acid and vice versa. If a salt has a component that is the conjugate of a weak acid, the salt will be weakly basic, and if it has a component that is the conjugate of a weak base, it will be acidic. However, if both components are conjugates of strong acids/bases, the salt will be neutral. Kw=Ka*Kb, so if Ka is extremely large, Kb must be extremely small to the point that it becomes negligible.

[Olivia Peony Dis 2A]

To add to what Bryan said, conjugate bases of strong acids are stable as its own (ion form) because the Ka for strong acids are large and thus the equilibrium is heavily shifted to the right (more product). Therefore the conjugate base won't make the solution basic, as it does not grab H+ ion from the surrounding (already stable). The same logic applies for conjugate acids of strong bases and vice versa for weak acids and bases conjugates.

Olivia Peony Dis 2A

[Jenny Han 3F]

To add onto the other replies, the strong acids and bases can be memorized by the provided lists, meaning that any molecule of H- that isn't there is a weak acid and any molecule of -OH that isn't there is a weak base. In context of salts, salts of strong bases and acids will not hydrolyze leading to a neutral solution, like NaCl composed of NaOH and HCl which is a strong base/acid.

[Eszter Kovacs 1A]

The ph of a salt depends on the strength of the acid and base that formed the salt. A strong acid and weak base will form a salt that is slightly acidic, a weak acid and strong base will form a salt that's basic, strong acids and strong bases form neutral salts.