Pok Oi Hospital Tang Pui King Memorial College

Second Term Test ( 1996-1997 )

F.4    Chemistry

Class                      :               ________________                           Date                  :     __________________

Name                      :               ________________                           Time allowed   :     60 mins

Class number.       :               ________________                           ( P.1 - P.6 /38 )

Instructions to students:

The total score of this paper is 100 marks.

Answer all questions.

Answer Section A and Section B in the foolscap papers provided.

Section A  (42%)

1.

    Which of the following will be observed during the above experiment?

    (1)    A reddish brown vapour will form.

    (2)    A silvery liquid will form.

    (3)    The glowing splint will relight.

    A.    (2) only

    B.    (1) and (2) only

    C.    (2) and (3) only

    D.    (1), (2) and (3)

2. When metals X, Y and Z are put into water, only X reacts ( colourless gas evolved).

    When put in an aqueous solution of Hg(NO₃)₂, only X and Z develop a layer of

    mercury. Reactivity is

    A.    X > Y > Z.

    B.    X > Z > Y.

    C.    Y > X > Z.

    D.    Y > Z > X.

3. When a small piece of sodium is put on water,

    (1)    it melts to give a silvery ball.

    (2)    an alkaline solution is formed

    (3)    it burns with a lilac flame.

    A.    (1) and (2) only

    B.    (1) and (3) only

    C.    (2) and (3) only

    D.    (1), (2) and (3)

4. An iron nail with its sharp end wrapped with zinc wire is placed in an agar with rust

    indicator. Which of the following will be observed after several hours?

5. Which conditions speed up the rate of rusting?

    (1)    presence of electrolyte

    (2)    high temperature

    (3)    mechanical treatment of the metal, or sharp edges

    A.    (1) and (2) only

    B.    (1) and (3) only

    C.    (2) and (3) only

    D.    (1), (2) and (3)

6. Which statement concerning simple chemical cells is INCORRECT?

    A.    The electrodes are usually made of two different metals.

    B.    The cell must contain an electrolyte.

    C.    The current flows from the more to the less reactive metal via the external wire.

    D.    The larger the difference in reactivities of the metal electrodes, the larger the

            voltage.

7. The oxidation number of chlorine is the highest in which compound?

    A.    Cl₂

    B.    NaOCl

    C.    NaCl

    D.    HCl

8. Which statement concerning an alkaline manganese cell is correct?

    A.    The anode is made of zinc.

    B.    The cell is rechargeable.

    C.    The cell is a secondary cell.

    D.    The electrolyte contains ammonium chloride.

9. Primary cell(s) include(s) the

    (1)    zinc-carbon cell.

    (2)    silver oxide cell.

    (3)    nickel-cadmium cell.

    A.    (1) only

    B.    (1) and (2) only

    C.    (1) and (3) only

    D.       (2) and (3) only

10. Graphite is commonly used as electrodes in electrolysis. Which of the followings are

      correct reasons?

      (1)    It is a good conductor of electricity.

      (2)    It does not form ions and is not attacked by chlorine.

      (3)    Its very high melting point enables it to be used as electrodes in the

              electrolysis of a hot molten compound.

      (4)    It is cheap.

    A.    (1) and (4) only

    B.    (2) and (3) only

    C.    (1), (3) and (4) only

    D.    (1), (2), (3) and (4)

11. Which of the following would affect the preferential discharge of ions in electrolysis?

      (1)    Voltage of the d.c. power supply

      (2)    Position of ions in the Electrochemical Series

      (3)    Relative concentration of the ions in the electrolyte

      (4)    Nature of the electrodes used

    A.    (1) and (4) only

    B.    (2) and (3) only

    C.    (1), (2) and (3) only

    D.    (2), (3) and (4) only

12. In the electrolysis of a concentrated aqueous solution of sodium chloride with

      graphite electrodes, which of the following is INCORRECT?

      A.    The ions present in the electrolyte are Na⁺ (aq), Cl^- (aq), H⁺ (aq) and OH^- (aq).

      B.    Cl^- (aq) and OH^- (aq) ions move towards the anode.

      C.    OH^- (aq) ions are preferentially discharged because they are more easily

              oxidized than Cl^- (aq) ions.

      D.    The solution becomes alkaline.

Directions: Questions 13-14 refer to the following set- up.

13. Which of the following statements is INCORRECT?

      A.    The set-up is an electrolytic cell.

      B.    The electrolyte is concentrated sodium chloride solution.

      C.    The anode is graphite.

      D.    The cathode is copper.

14. Sodium, but not hydrogen, is liberated at the cathode. This is because

      (1)    Na⁺ (aq) is a stronger oxidizing agent than H⁺ (aq).

      (2)    Na⁺ (aq) has a much higher concentration than H⁺ (aq).

      (3)    Mercury used as cathode favours the discharge of Na⁺ (aq).

      Which of the above are correct reasons?

    A.    (1) and (2) only

    B.    (1) and (3) only

    C.    (2) and (3) only

    D.    (1), (2) and (3)

Section B ( 58 % )

1. “ Food and beverage containers should NOT be made of aluminium. ”

    Do you agree with the above statement? Give your reasons. 

 ( 7 marks )

    ( 3 of the 7 marks for this question will be awarded for the effective communication of knowledge in Chemistry. )

 2. Iron sheets can be tin-plated by electrolysis of tin(II) compounds before they are used

    to make food cans.

    (a) What is the purpose of storing food in cans?

     (b) In the electrolysis of tin(II) compounds, what material should be made the anode?

     (c) (I)    Iron should be first tin-plated before food cans are made from it. Suggest a

                 reason.

          (II)   If the tin-plated iron sheet has been scratched to expose the iron, can it still be used to make a food can? Explain your answer.

          (III)  Explain why each of the following materials

                 (1)    steel plate

                 (2)    stainless steel plate

                 is not suitable for making food cans.

    (d) Iron can be galvanized.

         (I)    What is meant by ‘ galvanization ’?

         (II)   Can galvanized iron be used to make food cans? Explain.

                                                                                                         ( 10 marks )

3. In the apparatus shown, the beaker on side A contains iron(II) sulphate solution. The

    beaker on side B contains potassium dichromate solution and dilute sulphuric acid.

    The two beakers are joined by a salt bridge.

    The following reactions take place in the beakers.

    Side A: Fe²⁺ ® Fe³⁺

    Side B: Cr₂O₇^2- ® Cr³⁺

    (a) Balance each equation (if needed) and add state symbols.

     (b) In which beaker does oxidation occur? Explain.

     (c) In which beaker does reduction occur? Explain.

     (d) Combine the two half equations to give a balanced redox equation.

     (e) What is:  (I)    the oxidizing agent; and

                         (II)   the reducing agent?

     (f) The set-up in the diagram is a chemical cell. Explain why.

     (g) In which direction do electrons flow through the connecting wires? Explain.

     (h) Describe the colour changes in the two beakers.

                                                                                                    ( 17 marks )

4. The set-up shown below was used to compare the reactivity of four metals W, X, Y

and Z. The metal strips and copper sheet were first cleaned with sandpaper. The metal

strips were then placed in turn onto the filter paper, as shown below. In each case, the voltmeter reading was recorded.

    The results were as follows:

    (a) Why were the metal strips and the copper sheet first cleaned with sandpaper?

    (b) Which of the metal(s) is / are less reactive than copper? Explain your choice.

    (c) On the basis of the results shown, arrange the metals W, X, Y and Z in order of

         decreasing reactivity.

    (d) Given that Y is an element in group II of the Periodic Table, what would happen if it was placed in copper(II) sulphate solution? Write an ionic equation for the

         reaction involved.

    (e) Explain any difference in the voltmeter readings if the above experiments were repeated using a piece of filter paper soaked in methylbenzene (a non- electrolyte) instead of in sodium chloride solution.

                                                                                             (11 marks)

5. The diagram below shows the internal structure of a zinc-carbon cell.

     (a) Label parts A to F on the diagram.

     (b)Write the equation for the electrode reaction at negative pole.

     (c) Name the electrolyte of the cell.

     (d) (I)    State the oxidizing agent.

          (II)   Illustrate the function of the oxidizing agent with equation.

     (e) Do you think the above dry cell is really dry? Explain your answer.

     (f) State two differences between a new cell and used cell.

     (g) A dry cell often leaks after prolonged usage. Suggest a reason for this.

                                                                                           (13 marks)

END OF PAPER