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Metal Hydroxide - GCSE Chemistry Definition

Reviewed by: Richard Boole

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A metal hydroxide is a compound made of a metal ion and hydroxide ions (OH-). Metal hydroxides can form when a metal reacts with water or when a metal oxide reacts with water. These compounds act as bases, and many of them are alkaline, meaning they can dissolve in water to form solutions with pH above 7.

For example:

  • Sodium hydroxide (NaOH)

  • Calcium hydroxide [Ca(OH)2]

Metal hydroxides can turn red litmus paper blue and take part in neutralisation reactions with acids to form a salt and water:

metal hydroxide + acid → salt + water

Understanding metal hydroxides is important in GCSE Chemistry for explaining acid–base reactions, alkalinity, and their use in neutralising acids.

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Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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