Wednesday, 14 January 2015

4.4.3 - Laboratory Activity : Studying the reaction of halogens with aqueous sodium hydroxide solution.


Laboratory Activity 4.4.3:
Studying the reaction of halogens with aqueous sodium hydroxide solution.
Aim: To study the reaction between halogen and sodium hydroxide solution.
Problem statement: How do chlorine, bromine and iodine react with sodium hydroxide solution?
Hypothesis: Reactivity decreases for the reaction between halogen and sodium hydroxide solution when going down Group 17.
Variable:
» Fixed variable : sodium hydroxide solution
» Manipulated variable : Type of halogen
» Responding variable : Reactivity of reaction

Material:
» Chlorine gas
» Bromine solution
» Iodine crystals
» Sodium hydroxide solution

Apparatus:
» Rubber stopper
» Test tube
Procedure:

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

(A) With chlorine
1. Chlorine gas is into a test tube containing sodium hydroxide solution.
2. All observation are recorded.

(B) With bromine
1. The bromine liquid in the boiling tube is warmed up and the vapours are passed through hot iron wool.
2. The test tube is closed with a cork and shake well.
3. All observation are recorded.

(C) With iodine
1. A small iodine crystal is added to a test tube containing sodium hydroxide solution.
2. The test tube is closed with a cork and shake well.
3. All observation are recorded.
Results:

Halogen Observation
Chlorine Dissolves quickly. Greenish yellow colour of chlorine changes to colourless.
Bromine Dissolves less quickly. Forms colourless solution.
Iodine Dissolves slowly to form colourless solution.
Discussion:

Chlorine, bromine and iodine react with sodium hydroxide to form sodium halide, sodium hypohalite and water.

Chlorine dissolves quickly in sodium hydroxide solution to produce sodium chloride solution, sodium hypochlorite and water.
Cl2(g) + 2NaOH NaCl(aq) + NaClO(aq) + H2O(l)

Bromine dissolves less quickly in sodium hydroxide solution to produce sodium bromide solution, sodium hypobromite and water.
Br2(g) + 2NaOH NaBr(aq) + NaBrO(aq) + H2O(l)

Iodine dissolves slowly in sodium hydroxide solution to produce sodium iodide solution, sodium hypoiodite and water.
I2(g) + 2NaOH NaI(aq) + NaIO(aq) + H2O(l)

The reactivity of the halogens with sodium hydroxide solution decreases when going down Group 17.
Conclusion:

Halogens react with sodium hydroxide solution.

The reactivity increases down the Group 17.

The hypothesis is accepted.


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