AQA Chemistry 3 - Acids, Alkalis & Titrations

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Acid and Alkalis

Some compounds react with water to produce acidic or alkaline solutions

  • Acids (Proton donors) - Hydrogen ions
  • Alkalis (Proton acceptors) - Hydroxide ions

Strong acid or alkali completely ionises in water (H+).

  • Hydrochloric, Sulphuric and Nitric are strongly acidic
  • Sodium hydroxide and Potassium hydroxide are strongly alkali

Concerntration of H+ = 1mol/dm cubed

Weak acid or alkali only partially ionises in water (OH-).

  • Ethanoic, Citric and Carbonic are weakly acidic.
  • Ammonia solution is weakly alkali.

Concerntration of H+ = much less than 1mol/dm cubed


Titrations find out how much acid is needed to neutralise an alkali.

Choosing an indicator:

  • Strong acid + strong alkali - any indicator
  • Strong acid + weak alkali - menthyl orange
  • Strong alkali + weak acid -


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