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.