3C - The Halogens and displacement reactions
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3C - The Halogens and displacement reactions |
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1) State and explain the states of the halogens down Group 7: [3]
Gas - liquid - solid down the group [1] Due to increase in VDW [1] Due to more electrons [1]
2) This question is about the colours of the Halogens.
a) Complete the table below putting in the colours of the Halogens when dissolved in
water and a non polar solvent [6]
|
Halogen |
Colour in water |
Colour in non - polar solvent |
|
Chlorine |
pale green |
pale green |
|
Bromine |
orange |
orange |
|
Iodine |
brown |
purple |
b) Explain why the colours of chlorine and bromine become more intense
when dissolved in a non polar solvent [2]
The halogens are non polar molecules [1] they are more soluble in non - polar solvents [1]
Due to halogens and solvent having the same IMF
3) This question is about the displacement reactions of the halogens.
a) Copy and complete the following table as if the displacement reactions were carried out
using aq solutions. Put starting and final colours in the table [6]
|
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Potassium Chloride |
Potassium Bromide |
Potassium Iodide |
|
Chlorine |
x |
Pale green to Orange |
Pale green to Brown |
|
Bromine |
No reaction |
x |
Orange to Brown |
|
Iodine |
No reaction |
No reaction |
x |
Colour 1 [1] to colour 2 [1] x 3
b) Write balanced chemical reactions for each of the reactions in the table above, include state symbols [6]
Balanced equation [1] state symbols [1] x 3
Cl2(aq) + 2KBr(aq) à 2KCl(aq) + Br2(aq)
Cl2(aq) + 2KI(aq) à 2KCl(aq) + I2(aq)
Br2(aq) + 2KI(aq) à 2KBr(aq) + I2(aq)
c) The colour change in the reaction between bromine and potassium iodide is sometimes unclear
as bromine and iodine have similar colours when dissolved in water.
What could you add to the test tube to confirm that the colour is from iodine and not bromine?
State the change in colour you would observe. [2]
Brown to purple if iodine [1] Orange to brown if bromine [1]
4) Chlorine is added to water as a bleach to kill bacteria.
a) Write a balanced chemical equation for the reaction between chlorine and water: [2]
Cl2(aq) + 2H2O(l) à HCl(aq) + HClO(aq) Equation [1] Balanced [1]
b) Assign oxidation numbers to chlorine in (a): [3]
Cl2(aq) + 2H2O(l) à HCl(aq) + HClO(aq)
0 -1 +1 Each correct Ox No [1] x 3
c) Use your answers to (a) and (b) to describe what type of reaction this is: [3]
Disproportionation [1] as Cl is both oxidised [1] and reduced [1]