REDOX REACTIONS FOR CARIBEAN SECONDARY EXAMINATION

Redox Reactions for CSEC Chemistry

1. Oxidation and Reduction
Ms. Haynes

2. Define oxidation and
reduction; Loss and gain
of electrons and a
change in oxidation
number.
01
Investigate the action of
common oxidising and
reducing substances in
everyday activities
Identify oxidation and
reduction reactions
including reactions at
electrodes;
Objectives: Students should be able to
03
02
04
Deduce oxidation
number from formulae;

3. Objectives: Students should be able to
O5
06
Distinguish between oxidising
and reducing agents;
Perform tests for oxidising
and reducing agents

4. Define oxidation and reduction; Loss
and gain of electrons and a change in
oxidation number.
01

5. Oxidation
Oxidation is the loss of one or more
electrons from an atom or ion.
Oxidation was regarded as the gain of
oxygen or the loss of hydrogen from a
substance.
Old Definition Modern Definition

6. Reduction
Reduction is the gain of one or more
electrons by an atom or ion.
Reduction was seen as the loss of oxygen
or the gain of hydrogen by a substance.
Old Definition Modern Definition

7. Oxidation and Reduction
OXIDATION AND REDUCTION TAKE PLACE SIMULTANEOUSLY .
A substance will not loose electrons unless there is another substance available to gain the electrons. i.e
for every oxidation reaction there will be a reduction reaction.

8. Action of common oxidising and
reducing substances in everyday
activities
02
How present is it in our daily lives?

9. Rusting
●When Iron and its alloys, steel come into contact
with oxygen and moisture the iron is oxidized by
the oxygen to form hydrated iron (iii)) oxide
(????????????
2??????
3.x??????
2??????) otherwise known as rust.
●Given sufficient time and exposure to oxygen
and moisture any iron object will eventually
oxidiseentirely to rust and disintegrate.
https://www.youtube.com/watch?v=qd2B9yCKzc0

10. Browning of cut fruits
and vegetables
●Once the surface of certain fruits are exposed to
oxygen in the air, enzymes at the surface of the
fruit or vegetable begins to oxidisecertain
chemicals in the cells to brown compound
known as melanins.
●These melaninscause the cut or damaged surface
to turn brown.

11. Action of Bleaches
●Bleach is added to clothes to remove colored
stains. The most used bleaches are chlorine
bleaches containing sodium chlorate (I) and
oxygen bleaches containing hydrogen peroxide.
●Both types of bleach remove stains by oxidising
the colored chemicals or dyes to their colourless
form

12. Action of bleaches

13. Food Preservation
●Sodium sulfite and Sodium dioxide are used as
food preservatives.
●They do this by preventing oxidation
●They prevent bacteria from oxidising wine to
vinegar and prevent vitamin c in fruit juice being
destroyed by oxidation.
●Prevent browning of dried fruits, potato products
and shrimp by reducing chemicals produced during
the browning process back to their colorless form.

14. Deduce oxidation number from
formulae;
03

15. Rules for determining oxidation numbers
Oxidation occurs when the oxidation number of an element increases, i.e. gets more
positive and Reduction occurs when the oxidation number of an element decreases, i.e. gets less
positive.
The oxidation number of any element is zero.
1
(I) The oxidation number of the metal in an ionic compound is positive and
equal to its valency ( the combining capacity of an atom).
(II) The oxidation number of the non-metal in an ionic compound is negative
and equal to its
valency.
(III) The sum of the oxidation numbers of the atoms present in one formula of a
compound is
equal to zero.
2

16. Rules for determining oxidation numbers
The oxidation number of a simple ion is equal to the charge on the ion.3
The sum of the oxidation numbers of the atoms within an ion containing more
than one kind of
atoms is equal to the charge on the ion.
4

17. Try These !!
1.Determine the oxidation number of:
a.Copper in ????????????�
b.Sulfur in ??????
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c.Carbon in??????�,??????�
�,??????
�??????�
�????????????????????????
�??????
�
d.Nitrogen in�??????
�,�??????
��
�??????????????????�??????
�????????????
e.Chlorine in????????????????????????
�??????????????????�??????????????????�
Answers
a.+2
b.-2
c.+2, +4,+4 and -2
d.-3, -3and -3
e.-1and +1 and +5

18. Exceptions to the Rules
The oxidation number of hydrogen is always +1 EXCEPT in metal hydrides when
it is -1.
5
The oxidation number of oxygen is always -2 EXCEPT in peroxides when it is -1.
4

19. Identify oxidation and reduction
reactions including reactions at
electrodes;
04

20. Steps in writing half equations
●Write the balance overall equation
●Write the Ionic equation and remove the spectator
ions.
●Write the oxidation half equation (electrons on the
right) and reduction half equation
●(electrons on the left).
https://www.youtube.com/watch?v=jyvcVjrZnJA&t=13
s

23. Let’s Try !!!

24. Answers
Use oxidation number to determine whether the following are redox reactions:
a. Cl2(g) + 2KI(aq):
oOxidation: KI (I goes from -1 to 0)
oReduction: Cl2 (Cl goes from 0 to -1)
oYes, it’s a redox reaction.
●b. 4Al(s) + 3O2(g):
oOxidation: Al (Al goes from 0 to +3)
oReduction: O2 (O goes from 0 to -2)
oYes, it’s a redox reaction.

25. Answers
●c. Mg(s) + 2HCl(aq):
oOxidation: Mg (Mg goes from 0 to +2)
oReduction: H+ (H goes from +1 to 0)
oYes, it’s a redox reaction.
●d. BaCl2(aq) + H2SO4(aq) → 2KCl(aq) + BaSO4(s):
oNo, this is not a redox reaction; no change in oxidation states.

26. Answers
●e. 2Al2O3(S) → MgCl2(aq) + H2(g):
oNo clear assignment of oxidation states without specific reactants. If there is any change, it may indicate a
reaction, but generally not directly defined as redox without further context.
●f. BaSO4(s) + 2HCl(aq):
oNo, this is not a redox reaction; no change in oxidation states.

27. Oxidation and Reduction with an Electrolytic cell

28. Distinguish between oxidising and
reducing agents;
05

29. Oxidisingand Reducing
agent
An oxidizing agent (oxidant) is a substance that gains
electrons in a chemical reaction, causing another
substance to be oxidized (lose electrons), while a
reducing agent (reductant) is a substance that loses
electrons, causing another substance to be reduced
(gain electrons).
In the process oxidizing agent
becomes reduced and reducing agent
becomes oxidized.

30. Perform tests for oxidising and
reducing agents
06

31. Test for Oxidising and Reducing Agents