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Q19.

1.Pollutant Y is acidic.

2.When pollutant Y dissolves in rain water

3.it produces acid rain// causes air pollution.

Pollutant Y causes

1.Corroding/  corrode building.

2.Kill plants// increases acidity of soil// decreases pH of soil.

3.Kill aquatic organism// less.

●

Reject: destroy

 

 

 

 •Hard water contains Mg2+   and Ca2+

•   A – detergent

•   B  - Soap

Answer to Selected Topics 2012

Q17

Procedure

1.Measure [20 -200] cm3 of sodium hydroxide [0.1-2.0] mol dm-3 solution.

2.Pour the solution into a polystyrene cup.

3.Record the initial temperature of the solution.

4.Measure [20 – 200] cm3 of hydrochloric acid [0.1 – 2.0] mol dm-3.

5.Pour the solution into another polystyrene cup.

6.Record the initial temperature of the solution

7.Pour hydrochloric acid into sodium hydroxide solution.

8.Stir the mixture.

Record the highest temperature reached.                (7 marks)

Working

•Initial temperature of hydrochloric acid = T1

•Initial temperature of sodium hydroxide = T2

•Average initial temperature =  = Ta

•Highest temperature = Tb

•Heat given out = 200 x 4.2 x (Tb  - Ta) = x J                  1 mark

•Heat of neutralization =  -x/0.1 /1000    kJ mol-1                                 

                                      or         -x/0.1     J mol-1                  1mark

Answer to Essay Writing 2012

Q16.

Conversion of Fe3+ to Fe2+ ion

1.Reducing agent : Magnesium/ zinc/ any metal which is more electropositive than Fe (reject potassium, sodium and calcium)

2.Add [magnesium] to iron (III) chloride solution. (must be a soluble salt)

3.Stir/ shake/ Heat

4.Filter

5.Green precipitate is formed when sodium hydroxide  solution is added drop by drop until in excess. Or

  Dark blue precipitate formed when potassium hexacyanoferrate (III) solution is added.

Conversion of Fe2+ to Fe3+ ion

1.Oxidising agent as halogen:  Chlorine/ Bromine

2.Add chlorine water to solution of iron (II) sulphate.

3.Stir/ Shake/ Warm

4.Add sodium hydroxide solution or  potassium hexacyanoferrate (II) solution

5.Brown precipitate/ dark blue precipitate/blood red solution is formed.