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Hydrolysis of Salts

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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

A QUICK Tip to determine acidity or basicity of a salt:

1. split the salt into cation and anion
   

2. add OH^- to the cation (the positive ion)
   

   a. if you obtain a strong base. the cation is neutral  (NaOH, KOH, LiOH, Mg(OH)_{2 ...}etc.)
   b. if these are not formed it is an acidic ion
   

3. Add H⁺ to the anion (the negative ion)

   a. if you obtain a strong acid, the anion is neutral (HCl, HNO₃, HClO₄, HBr...)
   b. if none of these are formed you have a basic ion
   

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.

EXAMPLES

SODIUM ACETATE                                  NaC₂H₃O₂ <=> Na⁺ + C₂H₃O₂^-

Na⁺ + OH^- ==> NaOH (Strong Base....Na⁺ is neutral)

H⁺ + C₂H₃O₂^- ==> HC₂H₃O₂  (not a strong acid, so acetate is a basic ion)

So what really happens to these ions in water?

Sodium acetate dissolves                                                       NaC₂H₃O₂ <=> Na⁺ + C₂H₃O₂^-

In the presence of water, C₂H₃O₂^-  undergo hydrolysis:         H₂O + C₂H₃O₂^-  => HC₂H₃O₂^- + OH^-

NOTE HC₂H₃O₂ is a weak acid and will form (does not break up in water).

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

AMMONIUM CHLORIDE

It also dissolves                                                                      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.

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