Edexcel A-Level Chemistry AS 8.5 Oxidation and Reduction in Terms of Electron Transfer and Changes in Oxidation Number and the Application of These Ideas Questions

Label the relevant oxidation states before and after reaction, then state that an increase is oxidation and a decrease is reduction while naming both elements.

Exam points

Assign before-and-after oxidation numbers to prove that a reaction is redox.
Name the oxidised and reduced elements from increases and decreases in oxidation number.
Connect electron loss or gain to the corresponding oxidation-number change.

[Maximum number: 2]

This question is about the element calcium and some of its compounds.

Calcium reacts with chlorine to form calcium chloride.

\mathrm{Ca}(\mathrm{~s})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{~s})

Explain, in terms of oxidation numbers, why this is a redox reaction.

An explanation that makes reference to

Ignore explanations in terms of electron loss/gain

the following points:
```
- calcium/Ca oxidised
and
from 0 (in Ca ) to (+)2 (in $\mathrm{CaCl}_{2}$ )
```

```
- chlorine/ $\mathrm{Cl}_{2} / \mathrm{Cl}$ reduced
and
from 0 (in $\mathrm{Cl}_{2}$ ) to -1 (in $\mathrm{CaCl}_{2}$ )
```

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Edexcel A-Level Chemistry AS 8.5 Oxidation and Reduction in Terms of Electron Transfer and Changes in Oxidation Number and the Application of These Ideas Questions question 1