9701 · 6.1
Redox processes: electron transfer and changes in oxidation number (oxidation state) flashcards
Revision flashcards for Cambridge 9701 Redox processes: electron transfer and changes in oxidation number (oxidation state) (syllabus 6.1). Flip, recall, then mark a real past-paper question.
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What is a redox reaction?
A reaction involving both reduction and oxidation, characterised by the transfer of electrons and changes in oxidation numbers.
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Define oxidation using the acronym OIL.
Oxidation Is Loss of electrons. This corresponds to an increase in oxidation number.
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Define reduction using the acronym RIG.
Reduction Is Gain of electrons. This corresponds to a decrease in oxidation number.
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What is an oxidising agent (or oxidant)?
A species that accepts electrons and gets reduced in a redox reaction. It causes another species to be oxidised.
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What is a reducing agent (or reductant)?
A species that donates electrons and gets oxidised in a redox reaction. It causes another species to be reduced.
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What is the oxidation number of an atom in an uncombined element?
Zero. For example, in $\text{Na(s)}$, $\text{O}_2\text{(g)}$, and $\text{P}_4\text{(s)}$, the oxidation number of each atom is 0.
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What is the oxidation number of a simple monatomic ion?
The charge on the ion. For example, $\text{Na}^+$ has an oxidation number of +1, and $\text{S}^{2-}$ has an oxidation number of -2.
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What is the usual oxidation number of oxygen in a compound? Name one exception.
Usually -2. An exception is in peroxides (e.g., $\text{H}_2\text{O}_2$), where it is -1. Another is in compounds with fluorine (e.g., $\text{OF}_2$), where it is +2.
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What is a disproportionation reaction?
A redox reaction where an element in a single species is simultaneously oxidised and reduced to form two different products.
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What is the sum of oxidation numbers in a neutral compound?
Zero. For example, in $\text{H}_2\text{SO}_4$, the sum of all oxidation numbers is 0.
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What is the sum of oxidation numbers in a polyatomic ion?
The overall charge of the ion. For example, in the sulfate ion, $\text{SO}_4^{2-}$, the sum of oxidation numbers is -2.
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What is the oxidation number of hydrogen in most compounds? Name the exception.
Usually +1. The exception is in metal hydrides (e.g., $\text{NaH}$, $\text{CaH}_2$), where it is -1 as it is more electronegative than the metal.