Heep Woh College

Form 5 Chemistry Assignment 3

Section Seven : Fossil Fuel (Part II)

Suggested Answers

       

1.    (a)        Steam / water vapour                                                                                            1

              

        (b)  (i)        Carbon dioxide: Complete combustion of petrol.                                  1

                       (ii)        Carbon monoxide: Incomplete combustion of petrol.                          1

(iii) Oxides of nitrogen: Nitrogen and oxygen in air combine at high temperature. 1

 

        (c)  (i)        Alkene.                                                                                                                   1

                               General formula: C_nH_2n                                                                                        1

 

                       (ii)        Test with acidified potassium permanganate.                                              1

                               Alkene decolourizes potassium permanganate                                              1

                               while alkane does not.                                                                                          1

                       OR        Test with bromine solution.                                                                                   (1)

                               Alkene decolourizes bromine solution immediately                                    (1)

                               while alkane does not.                                                                                          (1)

              

                (iii)        C₄H₁₀ ¾® C₄H₈ + H₂           Accept other possible answers.                       1

 

(iv) Because the smaller molecules formed in cracking have higher demand. 1

                       OR        Because the smaller molecules formed in cracking are more useful.

E.g. Cleaner fuel, raw material of making plastics. (1)

 

        (d        2C₈H₁₈ + 25O₂ ¾® 16CO₂ + 18H₂O                                                                       1

                               No. of moles of C₈H₁₈ burnt   

                       =        5.7 / (12x8+1x18)

                       =        0.05                                                                                                                         1

                               Volume of air required

                       =        0.05 x 12.5 x 24 x 100/20

                       =        75 dm³                                                                                                                        1

 

2.    (a)  Solid A: yeast                                                                                                                 1

               Gas B: Carbon dioxide                                                                                             1

 

        (b) < 18% by volume.                                                                                                           1

                Yeast are inactive in high alcohol concentration.                                        1

 

        (c)  (i)        Fractional distillation                                                                                            1

               (ii)        Any one of the following answers:

                       whisky / brandy / volka / gin.                                                                      1

 

        (d)        Ethanol is oxidized to ethanoic acid in air.                                                         1

                CH₃CH₂OH + 2[O] ¾® CH₃COOH + H₂O                                                             1

        (e)  Liver damage / stomach ulcers / cancer of mouth, throat, gullet /

                brain damage …… accept other possible answers          Any TWO              2

 

        (f)        Making ethanoic acid, medicine, solvent, ……

               (Not accept making vinegar, wine)                                                                  2

 

3.    (a)  (i)         Ethene / CH₂=CH₂ / C₂H₄                                                                                   1

               (ii)  H₂O / Conc. H₃PO₄  or Conc. H₂SO₄                                                1,1

 

        (b)  (i)        Sodium

(ii)        Sodium floats / dissolves.                                                                                  1

Colourless gas bubble give out.                                                               1

 

        (c)  (i)        Reflux (Refer to NOTE)

Label – 1 mark; Diagram – 1 mark                                                             2

               (ii)        CH₃CH₂OH + 2[O] ¾® CH₃COOH + H₂O                                                     1

 

        (d)  (i)        ethyl ethanoate                                                                                           1

               (ii)        ethanoic acid; conc. H₂SO₄; reflux / heat / warm                                   1x3

(iii) Pour the reaction mixture into Na₂CO₃ solution to remove unreacted ethanoic acid. 1

                       Fruity / pleasant smell indicates the presence of ester.                            1

 

 

The End