Wednesday, 14 January 2015

4.4.1 - Laboratory Activity : Studying the reaction of chlorine, bromine and iodine with water

Laboratory Activity 4.4.1:
Studying the reaction of chlorine, bromine and iodine with water
Aim: To study the reaction between halogen with water.
Problem statement: How do chlorine, bromine and iodine react with water?
Hypothesis: Reactivity decreases for the reaction between halogen and water when going down Group 17.
Variable:
» Fixed variable : Water
» Manipulated variable : Type of halogen
» Responding variable : Reactivity of reaction

Material:
» Chlorine gas
» Bromine solution
» Iodine crystals
» Blue litmus paper
» Water

Apparatus:
» Delivery tube
» Rubber stopper
» Teat pipette
» Test tube
Procedure:

The animation below shows the procedures and observation of the experiment.

(A) With chlorine
1. Chloride gas is passed into some distilled water in a test tube.
2. The solution is then tested with blue litmus paper.
3. All observation are recorded.

(B) With bromine
1. A few drops of liquid bromine are added into distilled water.
2. The solution is then tested with blue litmus paper
3. All observation are recorded.

(C) With iodine
1. A small iodine crystal is added to distilled water.
2. The test tube is closed with a cork and shake well. The solution is then tested with blue litmus paper.
3. All observation are recorded.
Results:

Halogen In water With blue litmus paper
Chlorine Dissolves quickly. Forms a light yellow solution. Blue litmus turns red, then white (bleached)
Bromine Dissolves slowly. Forms a brown solution. Blue litmus turns red, then white(bleached)
Iodine Dissolves slightly. Forms a yellow solution. Blue litmus turns red, but not bleached
Discussion:

Chlorine, bromine and iodine react with water.

Chlorine dissolves in water to produce a mixture of hydrochloric acid and hypochlorus acid. The light yellow solution is called chlorine water(chlorine solution).
Cl2(g) + H2O(l) HCl(aq) + HOCl(aq)
Chlorine water is a bleaching agent. It bleached red litmus paper.

Bromine dissolves slowly in water to produce a mixture of hydrobromic acid and hypobromus acid. The brown solution is called bromine water (bromine solution).
Br2(g) + H2O(l) HBr(aq) + HOBr(aq)
Bromine water is a bleaching agent but less effective compared to chlorine water. It bleached red litmus paper.

Iodine does not dissolve easily in cold water. It only dissolves slightly in hot water to produce a mixture of hydroiodic acid and hypoiodus acid. The brownish yellow solution is called iodine water(iodine solution).
I2(g) + H2O(l) HI(aq) + HOI(aq)
Iodine water is not a bleaching agent.

The reactivity of the halogens with water decreases when going down Group 17.
Conclusion:

Halogens react with water to produce an acidic solution.

The reactivity increases down the Group 17.

The hypothesis is accepted.


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