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). ○ ${\mathrm{Cl}}_2\mathrm{(g)\; +}{H}_2\mathrm{O(l)}\to \mathrm{HCl(aq)\; +\; HOCl(aq)}$ 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). ○ ${\mathrm{Br}}_2\mathrm{(g)\; +}{H}_2\mathrm{O(l)}\to \mathrm{HBr(aq)\; +\; HOBr(aq)}$ 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). ○ ${\mathrm{I}}_2\mathrm{(g)\; +}{H}_2\mathrm{O(l)}\to \mathrm{HI(aq)\; +\; HOI(aq)}$ 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.

↶ 4.4 Group 17 Elements

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