Topic 9Reactions

of Acids

Acids and Metal Oxides• Farmers often use lime to reduce the

acidity of their soil. Lime is a metal oxide- calcium oxide.

• Metal oxides will neutralise acids to form a salt and water.

Metal oxide + Acid Salt + Water

Magnesium oxide + Carbonic Acid Magnesium carbonate + water

MgO + H2CO3 MgCO3 + H2O

Copper (II) oxide + sulphuric acid Copper sulphate + Water

CuO + H2SO4 CuSO4 + H2O

• In this reaction the H+ ions from the acids are reacting with the O2- ions from the metal oxide to form water:

2H+ + O2- H2O

The other ions present are spectator ions.

Preparation of these Salts

1. An insoluble metal oxide is used e.g. copper (II) oxide

2. Excess metal oxide is added to the acid e.g. sulphuric acid and warmed gently.

3. When the reaction is complete, excess metal oxide can be removed by filtration.

4. The solution (filtrate) is evaporated to dryness to obtain a solid sample of the product.

• Everyday example: Farmers often use lime to reduce the acidity of their soil. Lime is a metal oxide- calcium oxide.

Bases• A base is a substance which neutralises

an acid.• Examples of bases: alkalis (metal

hydroxides), metal oxides and metal carbonates are all examples of bases.

• An alkali is made if the base dissolves in water. The data book shows which bases dissolve in water. Examples: carbonates and hydroxides of Group 1 elements, of some Group 2 elements, and ammonium compounds.

• Metals do not dissolve in water.

Metal Compounds

AlkalisBases

Preparation of Compounds by Neutralisation and Evaporation

N.B.• This method is easier than using

soluble neutralisers (titration or pH paper) because:

1. Unreacted neutraliser can be removed easily (filtration)

2. End-point not over-shot (think about the first experiment with acids and alkalis)