POK OI HOSPITAL TANG PUI KING MEMORIAL COLLEGE

 FIRST TERM TEST ( 1997-1998 )

S7  CHEMISTRY

Class                :           7 S                                           Date     :           __________________

Name               :           ________________                Time allowed: 90 minutes

Class Number  :           ________________                ( P.1 - P.5 /38 )

Instructions to students:

1. Answer ALL questions.

2. Write your answers on the foolscap papers provided.

3. The total score is 100 marks.

4. The Periodic Table is printed on the last page.

Section A ( 52% )

1 There are more compounds which contain carbon atoms than the total of all known

  compounds which do not. What factors do you think are primarily responsible for the

   great number and diversity of carbon compounds?

                                                                                                            ( 6 marks )

2. Give the IUPAC names for the following compounds:

                                            ( 5 marks )

3. Explain the tetrahedral arrangement of the bonds in methane. When the groups

   attached to a carbon atom are all different from each other, the compound exhibits a

   special property. What is this property and by what means can it be measured? Suggest

     an example of such a compound using the smallest number of atoms

     possible.                                                                                          ( 7 marks )

4. Arrange the following carbonyl compounds in order of increasing boiling point:

                              CH₃COOH, CH₃CONH₂, CH₃COCH₃.

    Explain the order you have chosen.                                                ( 8 marks )

5. X is a liquid containing 48.7 % carbon, 8 % hydrogen and 43.3 % oxygen. Its relative

    molecular mass is approximately 100. X does not give any precipitate with

    2,4 - dinitrophenylhydrazine. Suggest possible structures for X.

                                                                                                            ( 10 marks )

6. Compare the reactions of ethanol with those of phenol, making particular reference to

    the following reagents: 

    (a) hydrogen bromide

    (b) sodium

    (c) aqueous sodium hydroxide.

         Give equations where appropriate.                                            ( 8 marks )

7. Give the structural formula of the major organic product(s) expected for the following

    reactions: 

                                                                                                              ( 8 marks )

Section B ( 48% )

8. Bromoethane can be prepared in the laboratory by the reaction between CH₃CH₂OH

    and HBr: 

CH₃CH₂OH + HBr  =  CH₃CH₂Br + H₂O

  The following procedure describes this preparation using the apparatus as shown in the diagram.

A measured volume of concentrated sulphuric acid was poured slowly into a sample of ethanol in flask P, which was kept cooled. A weighed amount of powder potassium bromide was added to the flask P, which was then immediately connected to device Q. Flask P was heated and the products formed soon began to distill over through device Q and adaptor R into the collecting flask S.

     (a) What is Q called? What was its function in the experiment?

     (b) Why was adaptor R arranged to dip below the surface of the water in flask S?

     (c) Why should adaptor R and flask S not be connected by an airtight stopper?

     (d) Write an equation to show how HBr is generated.

    (e) Upon heating, the reaction mixture turned orange. Why was this?

    (f) If a small amount of water had been added to the original mixture in flask P, more

        bromoethane would have been produced. Why?

     (g) Name two by- products that could be formed during the experiment.

     (h) Calculate the theoretical amount ( in grams ) of bromoethane obtained if the

            quantities of the reactants used were: 16g of ethanol, 12g of potassium bromide

             and excess concentrated sulphuric acid.

     (I) Can the procedure described above be used to prepare iodoethane if potassium

        iodide is used instead of potassium bromide? Explain.

                                                                                                              ( 18 marks )

9. Imagine that you have been given the following groups of organic chemicals. Outline

     simple chemical tests, together with the expected observation, which would enable you to

     identify each organic chemical.

     (a) CH₃CHO and CH₃COCH₃

     (b) CH₃COCH₃ and C₂H₅COC₂H₅

     (c) CH₃CH₂CH₂CHO and CH₃CH₂CH₂CH₂OH

     (d) CH₃CH = CHCH₂OH, CH₃CH₂CH₂CHO and

                                                                                                            ( 15 marks )

10. A bromoalkane A, C₅H₁₁Br, reacts rapidly with water to form an alcohol B,

      C₅H₁₂O which gives a negative iodoform test. When the bromoalkane A is treated

      with sodium ethoxide in an attempt to convert it to an ether C, the only product

      obtained is an alkene D, C₅H₁₀. Treatment of the alkene D with ozone followed by

      Zn/ dilute acid gives two carbonyl compounds as products, a ketone E, C₃H₆O and 

      an aldehyde F, C₂H₄O.

       (a) Deduce the structures of the compounds A to F.

       (b) Suggest a reason why the ether C cannot be prepared by the above procedure.

       (c) Suggest a scheme whereby the ether C may be prepared from A.

       (d) Describe the mechanism for the reaction of D with bromine water.

                                                                                                            ( 15 marks )

END OF PAPER