Acids and alkalis

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Acids, Alkalis and Bases


  • pH < 7
  • Turns litmus paper/ universal indicator red
  • Forms solutions containing H  ions


  • pH > 7
  • Turns litmus paper/ universal indicator blue
  • Forms solutions containing OH  ions


  • All alkalis are bases, but not all bases are alkalis
  • Alkalis are soluble bases
  • Substances that react with acids by absorbing H  ions
  • Oxides, hydroxides, carbonated etc
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Acid + Base/ Alkali = Salt + Water

Acid + Metal oxide = Salt + Water

Acid + Metal = Salt + Hydrogen

Salt + Salt = Diff. Salt and Diff. Salt (see precipitation)

Acid + Carbonate = Salt + Water + Carbon Dioxide

Acid + Alkali:

  • Water is formed because the H  ions react with the OH  ions to form H O
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Precipitation Reactions

  • Any reaction that produced an insoluble compound when two aqueous solutions are mixed
  • It is impossible to predict unless we know the physical state of all the reactants and products

aq + aq = s + aq

To work out whether a precipate is formed:

  • Write down the names of the reactants
  • Write down the ions in the reactants
  • Swap the ions
  • If one of the resulting salts are insoluble a precipitate has been formed
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