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Learning objective

Recognize redox reactions by observing changes in oxidation numbers, including: (a) elements in their uncombined state have an oxidation number of zero (b) the oxidation number of a monatomic ion equals its charge (c) the total oxidation numbers in a compound sum to zero (d) the total oxidation numbers in an ion equal its charge.

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Cambridge IGCSE ChemistryChemical reactionsSupplement content

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Recognize redox reactions by observing changes in oxidation numbers, including: (a) elements in their uncombined state have an oxidation number of zero (b) the oxidation number of a monatomic ion equals its charge (c) the total oxidation numbers in a compound sum to zero (d) the total oxidation numbers in an ion equal its charge

  • This point belongs to Redox, especially Redox outcomes.
  • You need to be able to recognize redox reactions by observing changes in oxidation numbers, including: (a) elements in their uncombined state have an oxidation number of zero (b) the oxidation number of a monatomic ion equals its charge (c) the total oxidation numbers in a compound sum to zero (d) the total oxidation numbers in an ion equal its charge.
  • The key ideas to know are Identify and Explain.
  • Use the linked flashcards and practice questions to check recall, then practise applying the idea in an exam-style answer.

Key concepts

IdentifyExplain

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Paper 4 structured question: Redox

Paper 4Theory (Extended)1 marks

Description

Oxidation Number Rules

1. Uncombined elements have an oxidation number of 0. 2. The oxidation number of a monatomic ion equals its charge. 3. The total oxidation numbers in a compound sum to 0. 4. The total oxidation numbers in an ion equal its charge.

  1. a

    State the oxidation number of an uncombined element.

    Aim for approximately 1 distinct marking point.

    [1]
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