Edexcel IAL Chemistry 8.5 Oxidation and reduction

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 $\mathrm{CaCl}_{2}$ )
```

All question bank results loaded

8.5—Oxidation and reduction in terms of electron transfer and changes in oxidation number, and the application of these ideas question 1