REDOX REACTION
REDUCTION
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.
1 Prepared By Kartini Ishak
OXIDATION AND REDUCTION
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 oxygen
2) loss and gain of hydrogen
3) loss and gain of electrons
4) 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:
2 Prepared By Kartini Ishak
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 _______________________.
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.
3 Prepared By Kartini Ishak
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:
Na (s) Na+ (s) + e- oxidation – loss of electrons
Cl2(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 zero
E.g. O2, He, Na, C are all zero.
2) Simple ions have an oxidation number = charge on the ion
E.g. Na+ = +1, Al3+ = +3, S2- = -2
3) 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
4 Prepared By Kartini Ishak
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 _______________________.
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
5 Prepared By Kartini Ishak
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
COMMON OXIDISING AND REDUCING AGENTS
Please proceed to do exercise from:
WORKSHEET 3
WORKSHEET 4
6 Prepared By Kartini Ishak
WORKSHEET 1
WORKSHEET 2
7 Prepared By Kartini Ishak
WORKSHEET 3
8 Prepared By Kartini Ishak
WORKSHEET 4
9 Prepared By Kartini Ishak
