Hydrolysis of Salts

Acid-Base Properties of Salt Solutions:

• an ionic compound made of a cation and an anion, other than hydroxide.
• the product besides water of a neutralization reaction

determining acidity or basicity of a salt solution:

1. split the salt into cation and anion
   
2. add OH^- to the cation
   
   a. if you obtain a strong base. the cation is neutral
   b. if you get a weak base, the cation is acidic
   
3. Add H⁺ to the anion
   
   a. if you obtain a strong acid, the anion is neutral
   b. if you obtain a weak acid. the anion is basic
   
4. Salt solutions are neutral if both ions are neutral
   
5. Salt solutions are acidic if one ion is neutral and the other is acidic
   
6. Salt solutions are basic is one of the ions is basic and the other is neutral.
   
7. The acidity or basicity of a salt made of one acidic ion and one basic ion cannot be determined without further information.

Salts of Weak Acids

A¯ + H₂O --> HA + OH¯

Salts of Weak Bases

HB⁺ + H₂O --> B + H₃O⁺

EXAMPLES

SODIUM ACETATE                                  NaAc <=> Na⁺ + Ac^-

In the presence of water, Ac^- undergo hydrolysis:

H₂O + Ac^- = HAc + OH^-            ---> NOTE HAc is a weak acid and will form

This salt is BASIC due to the presence of OH^- in the reaction.

AMMONIUM CHLORIDE

NH₄Cl <=> NH₄⁺ + Cl^-

In the presence of water, NH₄⁺ undergo hydrolysis:

NH₄⁺ + H₂O<=> NH₃+ H₃O⁺

This salt is ACIDIC due to the presence of H₃O⁺ in the reaction.

 

KC2H3O2               BASIC	NaH2PO4       BASIC
Cu(NO3)2              ACIDIC	LiHS            BASIC