2.1.15 Salts

2.1.15 Salts

1. Salts

   • A salt is an ionic compound with:
     • The cation in a salt is usually a metal ion or ammonium, NH4+
     • The anion in a salt is derived from an acid
     • The formula of a salt is the same as the parent acid except a H+ ion has been replaced by the cation

2. Examples

   • Sulfuric acid, H2SO4 --> sulphate salts e.g. K2SO4
   • Hydrochloric acid, HCl --> chloride salts e.g. NaCl
   • Nitric acid, HNO3 --> nitrate salts e.g. Ca(NO3)2

3. Acid

   • Sulfuric acid has 2 H+ ions that can be replaced by a different + ion
   • If 1 H+ ion is replaced an acid salt is formed e.g. NaHSO4
     • H2SO4 --> NaHSO4
   • The acid salt can behave as an acid, because H+ ion can be replaced to from a conventional salt e.g. Na2SO4
     • NaHSO4 --> Na2SO4

4. Formation of salts

   • Salts can be produced by neutralising acids with bases such as:
     • Carbonates, these contain CO3 2-
     • Metal oxides
     • Alkalis, soluble base that forms OH- ions
   • Salts from carbonates
     • Acids react with carbonates to from a salt, CO2 and H2O
       • You will see bubbles of CO2
     • E.g. 2HCl (aq) + CaCO3 (s) --> CaCl (aq) + CO2 (g) + H2O (l)
     • E.g. 2H+ (aq) + CaCO3 (s) --> Ca2+ (aq) + CO2 (g) + H2O (l)
   • Salts from metal oxides
     • Acids react with metal oxides to form a salt and H2O
     • E.g. 2HCl (aq) + CaO (s) --> CaCl2 (aq) + H2O
     • E.g. 2H+ (aq) + CaO (s) --> Ca2+ (aq) + H2O (l)
   • Salts from alkalis
     • Acids react with alkalis to form a salt and H2O
     • E.g. HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O (l)
     • E.g. H+ (aq) + OH- (aq) --> H2O (l)
   • Salts from metals
     • Acids react with metals to from a salt and H2 gas
     • E.g. 2Li (s) + 2HCl (aq) --> 2LiCl (aq) + H2 (g)

5. Ammonium salts

   • When acids are neutralised by (aq) ammonia, ammonium salts are formed (containing ammonium ion NH4+)
   • E.g. Ammonium nitrate is formed when ammonia and nitric acid react:
     • NH3 (aq) + HNO3 (aq) --> NH4NO3 (aq)
   • When ammonium nitrate is found in solution, its found as NH4+ and NO3-