Chemistry C2 Part Four

Revision PowerPoint - Big ideas

Acids, alkalis and making salts

The pH scale

pH 1

pH 7

pH 14

Acidity and the pH scale

• Acids have a pH of less than 7 and are neutralised by bases.• Alkalis are soluble bases. Alkalis have a pH greater than 7.•Water is neutral, pH7

Acids and alkalis

• Acids contain hydrogen ions, H+• Alkalis contain hydroxide ions, OH–. • These react together to form water.

Acid + Base = Neutralisation!

• Metal oxides or hydroxides are bases; ammonia is also a base.• Bases react with the hydrogen ions produced by the acidsH+ + OH– → H2O2H+ + O2– → H2O

Making a salt

• Salts form when acids react with bases, alkalis or reactive metals.

• e.g. Acid + Reactive metalMg + H2SO4 → MgSO4 + H2

• e.g. Acid + BaseCuO + 2HCl → CuCl2 + H2O

Making soluble salts

Soluble salts are prepared by neutralisation (1) followed by crystallisation (3).e.g. copper sulphateCuO + H2SO4 → CuSO4

+ H2O

Precipitation reactions

Insoluble salts are made by precipitation reactions.Precipitation of clay is used in water treatment.