1. Halogens become less reactive down Group 17 as their oxidizing power decreases. Thus, a halogen higher in the group can displace one lower in the group from its salts. 2. Three displacement reactions are described where chlorine, bromine, and iodine displace bromide or iodide from solutions of their salts. 3. The products of each reaction are identified by the color they impart to the tetrachloromethane layer, with chlorine appearing pale yellow, bromine appearing orange, and iodine appearing purple.

1. By :SuziShaf
REDOX REACTION
Displacement of halogens from halide solution
Halogens : element in group 17
(chlorine, Cl2 , bromine, Br2 , and iodine, I2 )
Halides : element of ion in group 17
(chloride ion, Cl- , bromide ion, Br- and iodide ion, I- )
Still remember ?????
When go down group 17,
REACTIVITY of halogen decrease.
Why …..? (answer)
So, the power of halogen as oxidizing agent also decrease when go
down the group.
This means halogen at higher position in group 17 can displace
halogen at lower position, from it halides solution.
Thus;
There are three reactions that can take place.
Can you state all these three processes?
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2. By :SuziShaf
Halogen colour in tetrachloromethane is usually use to
identify the type of halogen presence.
Observe the reaction below:
i.
(shake the mixture
3 strongly)
2 cm
+tetrachloromethane →
solution
Colour of chlorine
2 cm3 chlorine water in
water solution tetrachlorometane
(pale yellow /colourless) (pale yellow / colourless)
ii.
(shake the mixture
2 cm3 strongly)
+ tetrachloromethane →
solution
2 cm3 Colour of bromine
bromine water water in
solution (brownish yellow) tetrachloromethane
(orange)
2

3. By :SuziShaf
iii.
(stronger shake the
3 mixture)
2 cm
+ tetrachlorometana →
solution
2 cm3 iodine Colour of iodine in
water/solution tetrachlorometane
(brown) (purple)
Complete the following table:
The colour in the
Colour in
aqueous solution
Halogen tetrachloromethan
concentrate
dilute e
d
Chlorine
water,Cl2
Bromine
water,Br2
Iodine
water, I2
Halogen can be identify by mixing the
tetrachloromethane agent solution to the aqueous
solution. Water and tetrachloromethane will not
3

4. By :SuziShaf
dissolve together but will form two layer. The upper
layer is water and below is tetrachloromethane layer.
Tips : look at the colour of the tetrachloromethane layer
to determine the halogen that presence.
Cl2 + 2KBr → Br2 + 2KCl
(shake the
(add and mixture
shake the strongly)
mixture)
+ + tetrachlorometane
3
3
2 cm potassium
2 cm
→
bromide solution
2 cm3 chlorine
water solution solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer :orange
Chlorine is more reactive than bromine, the strength
of oxidizing agent for chlorine is more stronger than bromine.
Thus chlorine will displace bromine from potassium bromide
solution. Orange colour in tetrachloromethane layer proved the
presence of bromine, Br2 in the mixture.
Chlorine is reduced to chloride ion.
Chlorine also act as oxidizing agent.
Half equation : Cl2 + 2e → 2Cl-
The oxidation number of chlorine is decreases from 0 to -1.
4

5. By :SuziShaf
1 molecule of chlorine gains 2 elctrons to form 2 chloride ions.
Thus, chlorine undergoes reduction process.
Bromide ion is oxidize to bromine.
Bromide ion also act as reducing agent.
Half equation : 2Br- → Br2 + 2e
The oxidation number for bromine is increases from -1 to 0.
2 bromide ions loses 2 electrons to become 1 bromine molecule
Bromide ions is undergoes oxidation
Total ionic equation :
Cl2 + 2Br- → 2Cl- + Br2
How this process is made?
Considered the following reaction;
Cl2 + 2KI → I2 + 2KCl
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6. By :SuziShaf
(stronger
(add and shake the
shake the mixture)
mixture)
+ + tetrachlorometane →
3
2 cm
solution
2 cm3 chlorine 2 cm3 potassium
water solution iodide solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer purple
Chlorine is more reactive than iodine,
Thus chlorine will displace iodine from potassium iodide
solution.
The purple colour in tetrachloromethane layer proved
the present of iodine, I2 in the solution.
Can you state all the following matter?;
Cl2 + 2e  2Cl-
2I-  I2 + 2e
i. Changes of oxidation number for chlorine in this reaction.
ii. Changes of oxidation number for iodine in this reaction.
iii. Substances that is oxidize : I-
iv. Substances that is reduced : Cl2
v. Oxidizing agent
vi. Reducing agent
vii. Half equation for oxidation process
viii. Half equation for reduction process
ix. Total ionic equation
x. Observation in the reaction above
6

7. By :SuziShaf
How this reaction is made?
Considered this reaction;
Br2 + 2KI → I2 + 2KBr
(stronger
(add and shake the
shake the mixture)
mixture)
+ + tetrachlorometane
3
) 2 cm
→
solution
2 cm3 2 cm3 potassium
bromine water iodide solution
solution
(brown) (colourless) Water layer: yellow
Tetrachlorometane layer :purple
Bromine is more reactive than iodine, so the power of oxidizing
agent for chlorine is more stronger than iodine. By that, bromine
will displace iodine from it potassium iodide solution. The purple
colour in tetrachlorometane layer prove the present of iodine, I2 in
the solution.
Can you state all the following matter?;
i. Changes of oxidation number for bromine in this reaction.
ii. Changes of oxidation number for iodine in this reaction.
iii. Substances that is oxidize
iv. Substances that is reduced
v. Oxidizing agent
vi. Reducing agent
vii. Half equation for oxidation process
viii. Half equation for reduction process
ix. Total ionic equation
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8. By :SuziShaf
x. Observation in the reaction above
(stronger
(add and shake the
shake the mixture)
mixture)
+ + tetrachlorometane
3
2 cm 3
2 cm
→
bromine water solution
2 cm3 potassium
solution iodide solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer :orange
(stronger
(add and shake the
shake the mixture)
mixture)
+ + tetrachlorometane
3
2 cm
→
solution
2 cm3 iodine 2 cm3 potassium
water solution iodide solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer :purple
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9. By :SuziShaf
(stronger
(add and shake the
shake the mixture)
mixture) 2 cm3
+ + tetrachlorometane →
solution
2 cm3 iodine 2 cm3 potassium
water solution bromide
solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer :purple
9

10. By :SuziShaf
(stronger
(add and shake the
shake the mixture)
mixture) 2 cm3
+ + tetrachlorometane →
solution
2 cm3 iodine 2 cm3 potassium
water solution bromide
solution
(pale yellow/ (colourless) Water layer: yellow
colourless) Tetrachlorometane layer :purple
9