REDOXDisplacement 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….

Why …..? (anwer)

So , the power of halogen as oxidizing agent also decrease when go down the group.

Thus; There are three reactions that can take place. Can you state all this three process?

When go down group 17,reactivity of halogen decrease.

This means halogen at higher position in group 17 can displace halogen at lower position, from it halides solution.

Halogen colour in tetrachloromethane is usually use to identify the type of halogen presence.

Observe the reaction above. i.

ii.

2 cm3 chlorine water solution

+ 2 cm3 tetrachloromethane

solution

→

(pale yellow /colourless)

Colour of chlorine water in tetrachlorometane

(pale yellow / colourless)

(shake the mixture strongly)

2 cm3 bromine water solution

+ 2 cm3 tetrachloromethane

solution→

(brownish yellow)

Colour of bromine water in tetrachloromethane

(orange)

(shake the mixture strongly)

iii.

Complete the following table;

HalogenThe colour in the aqueous solution Colour in

tetrachloromethanedilute concentrated

Chlorine water,Cl2

colourless Pale yellowColourless / pale yellow

Bromine water,Br2

yellowBrownish yellow

Orange/brown

Iodine water, I2

yellow Brown purple

Halogen can be identify by mixing the tetrachlormethane agent solution to the aqueous solution. Water and tetrachloromethane will not

2 cm3 iodine water/solution

+ 2 cm3 tetrachlorometana

solution

→

(brown)

Colour of iodine in tetrachlorometane

(purple)

(stronger shake the mixture)

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

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. 1 molecule of chlorine gains 2 elctrons to form 2 chloride ions.

2 cm3 chlorine water solution

+ 2 cm3 tetrachlorometane

solution

→

(pale yellow/ colourless)

(colourless)

2 cm3 potassium bromide solution

+

Water layer: yellowTetrachlorometane layer :orange

(add and shake the mixture)

(shake the mixture strongly)

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 moleculeBromide ions is undergoes oxidation

Total ionic equation :

Cl2 + 2Br- → 2Cl- + Br2

How this process is made?Considered the following reaction;

Cl2 + 2KI → I2 + 2KCl

2 cm3 chlorine water solution

+ 2 cm3 tetrachlorometane

solution

→

(pale yellow/ colourless)

(colourless)

2 cm3 potassium iodide solution

+

Water layer: yellowTetrachlorometane layer purple

(add and shake the mixture)

(stronger shake the mixture)

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-1 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 agentvii. Half equation for oxidation processviii. Half equation for reduction processix. Total ionic equationx. Observation in the reaction above

Contd 5.2How this reaction is made?Considered this reaction;

Br2 + 2KI → I2 + 2KBr

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 oxidizeiv. Substances that is reducedv. Oxidizing agentvi. Reducing agentvii. Half equation for oxidation processviii. Half equation for reduction processix. Total ionic equationx. Observation in the reaction above

(continue)

Ok, its sure that you had master in this reaction,so

2 cm3 bromine water solution

+ 2 cm3 tetrachlorometane

solution

→

(brown) (colourless)

2 cm3 potassium iodide solution

+

Water layer: yellowTetrachlorometane layer :purple

(add and shake the mixture)

)

(stronger shake the mixture)

Considered the following reaction;

2 cm3 bromine water solution

+ 2 cm3 tetrachlorometane

solution

→

(pale yellow/ colourless)

(colourless)

2 cm3 potassium iodide solution

+

Water layer: yellowTetrachlorometane layer :orange

(add and shake the mixture)

(stronger shake the mixture)

2 cm3 iodine water solution

+ 2 cm3 tetrachlorometane

solution

→

(pale yellow/ colourless)

(colourless)

2 cm3 potassium iodide solution

+

Water layer: yellowTetrachlorometane layer :purple

(add and shake the mixture)

(stronger shake the mixture)

2 cm3 iodine water solution

+2 cm3

tetrachlorometane solution

→

(pale yellow/ colourless)

(colourless)

2 cm3 potassium bromide solution

+

Water layer: yellowTetrachlorometane layer :purple

(add and shake the mixture)

(stronger shake the mixture)