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Acids & Alkali

Chemistry: Cambridge International GCSE Supplement, topic 7.1.1

Acids and Bases

Acids and alkalis are on the opposite ends of the pH scale. They combine to form water, which is neutral.

Acids

Acids

  • Acids are substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions).
  • Acids are proton (H+) donors.
Bases

Bases

  • A base is any substance that can neutralise an acid.
  • Bases are proton acceptors.
  • Bases can either be soluble or insoluble in water.
  • Soluble bases are known as alkalis, which are substances that release hydroxide (OH-) ions in aqueous solutions. These are typically metal hydroxides.
  • The two main types of insoluble bases you will need to know are metal oxides and metal carbonates.
Measured using pH scale

Measured using pH scale

  • The pH scale is used to measure how acidic or alkaline a substance is.

Test yourself on Acids & Alkali

  • Which of these are true of acids?

  • Which of these are true of alkalis?

  • Thinking about what ions form when they dissolve in water, why does mixing an acid and an alkali create a neutral substance?

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