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Redox equations for AQA A-level Chemistry

Redox equations

This page covers the following topics:

1. Redox half-equations
2. Reactivity of halogens
3. Redox equations

Reduction is the gain of electrons or the decrease of an oxidation number. Oxidation is the loss of electrons or the increase of the oxidation number. A particle gains electrons when it is reduced and a particle loses electrons when it is oxidised. Redox half-equations provide information about the change in particles and the loss or gain of electrons. Many half-equations can be balanced by adding electrons, water molecules and hydrogen ions.

Feยณโบ + eโป โ†’ Feยฒโบ (reduction)
Mg โ†’ Mgยฒโบ + 2eโป (oxidation)

Redox half-equations

The reactivity of halogens decreases going down the group 7 of the periodic table. A more reactive halogen displaces a less reactive halogen in a halide salt solution.

Reactivity of halogens

Redox half-equations can be combined to construct full ionic equations by matching the number of electrons and removing duplicate particles from both sides of an equation. If the electrons do not cancel out after adding half-equations, they can be multiplied by suitable integers beforehand. Both sides of a half-equation can also be switched around to ensure that electrons appear on both sides of an ionic equation. In a redox equation a reducing agent is an electron donor, while an oxidising agent is an electron acceptor.

Redox equations

1

Explain why iodine does not displace chlorine in sodium chloride that is dissolved in water.

A more reactive halogen displaces a less reactive halogen in halide salt solutions. The reactivity of halogens decreases going down the group 7 of the periodic table. Since iodine is lower down the group 7 than chlorine, it it is less reactive and does not displace chlorine in its salt.

Iodine is less reactive than chlorine.

Explain why iodine does not displace chlorine in sodium chloride that is dissolved in water.

2

Identify all particles that are reduced in the half-equations provided.

2Clโป โ†’ Clโ‚‚ + 2eโป
Mnโตโบ + 3eโป โ†’ Mnยฒโบ

A particle gains electrons when it is reduced. In these half-equations Mnโตโบ gains electrons.

Mnโตโบ

Identify all particles that are reduced in the half-equations provided.

2Clโป โ†’ Clโ‚‚ + 2eโป
Mnโตโบ + 3eโป โ†’ Mnยฒโบ

3

Provide a balanced chemical equation for the reaction that happens when chlorine is added to a calcium iodide solution.

A more reactive halogen displaces a less reactive halogen in halide salt solutions. Chlorine is more reactive than iodine, thus chlorine displaces iodine in the salt.

CaIโ‚‚ + Clโ‚‚ โ†’ CaClโ‚‚ + Iโ‚‚

Provide a balanced chemical equation for the reaction that happens when chlorine is added to a calcium iodide solution.

4

Which of the following half-equations could be combined together to create an ionic equation that corresponds to the reaction presented in the image?

A) Na โ†’ Naโบ + eโป
B) Clโ‚‚ + 2eโป โ†’ 2Clโป
C) Brโ‚‚ + 2eโป โ†’ 2Brโป

In the reaction bromine and chlorine change their oxidation numbers. Redox half-equations can be combined to construct full ionic equations by matching the number of electrons and removing duplicate particles from both sides of an equation. Both sides of a half-equation can also be switched around to ensure that electrons appear on both sides of an ionic equation.

B, C

Which of the following half-equations could be combined together to create an ionic equation that corresponds to the reaction presented in the image?

A) Na โ†’ Naโบ + eโป
B) Clโ‚‚ + 2eโป โ†’ 2Clโป
C) Brโ‚‚ + 2eโป โ†’ 2Brโป

5

Provide a balanced chemical equation for the reaction between fluorine and lithium bromide solution.

A more reactive halogen displaces a less reactive halogen in halide salt solutions. Fluorine is more reactive than bromine, thus fluorine displaces bromine in the salt.

2LiBr + Fโ‚‚ โ†’ 2LiF + Brโ‚‚

Provide a balanced chemical equation for the reaction between fluorine and lithium bromide solution.

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