REDOX REACTIONREDUCTION

OXIDATION

By the end of the topic, students should be able to:□ Know what is meant by a redox reaction.□ Define oxidation and reduction in terms of oxygen gain/loss and

use it to show where oxidation and reduction take place in a reaction.

□ Define oxidation and reduction in terms of hydrogen loss/gain and use it to show where oxidation and reduction take place in a reaction.

□ Define oxidation and reduction as electron loss/gain and use it to show where oxidation and reduction take place in a reaction.

□ Find the oxidation state of an element in a compound.□ Find the formula of a compound from its name containing an

oxidation number.□ Define oxidation and reduction in terms of changes in oxidation

state and use it to show where oxidation and reduction take place in a reaction.

□ Describe the colour change when potassium iodide is used to test for an oxidizing agent.

□ Describe the colour change when potassium manganate (VII) and potassium dichromate (VI) are used to test for a reducing agent.

□ State some common oxidizing and reducing agents.

Please tick in the box if you can do the above. OXIDATION AND REDUCTION

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In chemical reactions, oxidation and reduction is an important concept and it has applications in many topics.

There are several ways of describing oxidation and reduction. They can be described in terms of:1) loss and gain of oxygen2) loss and gain of hydrogen3) loss and gain of electrons4) change of oxidation state

1) LOSS AND GAIN OF OXYGEN

Gain of oxygen in a reaction is __________________. Loss of oxygen in a reaction is __________________.

Example 1:

Oxidising and reducing agent What is an oxidizing agent?A substance that causes another substance to be _______________.An oxidizing agent is _____________ when it oxidizes another substance.

What is a reducing agent?A substance that causes another substance to be _______________.A reducing agent is _______________ when it reduces another substance.

From example 1 above, state the oxidizing agent and the reducing agent.Oxidising agent:Reducing agent:

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 325, Questions, Quest. 1-2

2) LOSS AND GAIN OF HYDROGEN

Loss of hydrogen in a reaction is ______________________. Gainof hydrogen in a reaction is _______________________.

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Example 2:

From example 2 above, state the oxidizing agent and the reducing agent.Oxidising agent:Reducing agent:

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 325, Questions, Quest. 3

3) LOSS AND GAIN OF ELECTRONS

Loss of electrons in a reaction is _________________. Gain of electrons in a reaction is _________________.

Example 3:

From example 3 above, state the oxidizing agent and the reducing agent.Oxidising agent:Reducing agent:

IONIC HALF EQUATIONS

Redox reactions involving a transfer of electrons can be split into two halves.

One half equation shows oxidation while the other half shows

reduction.

In the reaction between sodium and chlorine, the two ionic half equations are:

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Na (s) Na+ (s) + e- oxidation – loss of electronsCl2(g) + 2e- 2Cl-(s) reduction – gain of electrons

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 328, Questions, Quest. 1-2.

OXIDATION STATE

What is an oxidation state?The oxidation state is the charge of an atom of an element would have if it existed as an ion in a compound (even if it is covalently bonded).

To work out the oxidation state of an atom, we apply the following rules:1) Elements are zeroE.g. O2, He, Na, C are all zero.2) Simple ions have an oxidation number = charge on the ionE.g. Na+ = +1, Al3+ = +3, S2- = -23) Hydrogen is +1 except when joined directly to metals (NaH, CaH2)4) Oxygen is -2 except in peroxides where it is -1 (H2O2, Na2O2)5) Compounds and radicals have their sum of oxidation numbers = total charge.E,g, SO2 S + 2O = 0

S + 2(-2) = 0 S = +4

Please proceed to do exercise from: WORKSHEET 1

NAMES OF COMPOUNDS

The oxidation state of an element in a compound can be indicated by a Roman number.e.g. Manganese (IV) oxide, means the manganese has oxidation state of +4 in the compound.

Oxidation state are usually only given in the names of compounds where an element can have more than one oxidation state.e.g. Magnesium always has oxidation state of _______ in compounds so the name of MgSO4 is ________________________. Iron can have oxidation state of +2 or +3 in compounds, so the name of FeSO4 is ______________________________.

4) CHANGE OF OXIDATION STATE

Increase in oxidation state is _______________________.

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Decrease in oxidation state is _______________________.

Oxidised: Reduced:Oxidising agent: Reducing Agent:

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 333, Questions, Quest. 1-3.

REDOX REACTION

UCTION IDATION

Redox reaction is the combined process of oxidation and reduction. There can be NO oxidation without reduction and vice versa.

Please proceed to do exercise from: WORKSHEET 2

TEST FOR OXIDISING AND REDUCING AGENT

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COMMON OXIDISING AND REDUCING AGENTS

Please proceed to do exercise from: WORKSHEET 3WORKSHEET 4

WORKSHEET 1

WORKSHEET 2

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WORKSHEET 3

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WORKSHEET 4

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