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中五化學/會考試題改編/短答題/ 1

    Name: S.5 Revision Exercise (2) Class. No.

    1. What is the colour of each of the following aqueous solutions? (4 marks)

     A. copper(II) sulphate blue B. nickel(II) sulphate green

     C. cobalt(II) chloride pink D. iron(III) sulphate) pale brown / yellow

    2. The formula of an oxide of X is XO. If 10.2 g of this oxide contains 5.4 g element X , what is the relative atomic mass 23

    of X? R.A.M.: O=16.0(2 marks)

     Let M be the relative atomic mass of X,

     In 10.2 g XO, mass of X = 5.4 g , so mass of O = 10.2 5.4 = 4.8 g 23

     5.4/X : 4.8/16 = 2 : 3

     so X = 27

3. 1 1M ethanoic acid 2 1M hydrochloric acid 3 1M aqueous ammonia

     Arrange the above solutions in increasing order of pH values. Explain your answer. (2 marks)

     (3) > (1) > (2).

     Ammonia is an alkali, so it has the highest pH value.

     Ethanoic acid is a weak acid. It has a lower hydrogen ions concentration than that of hydrochloric acid. So the pH value of

     ethanoic acid is higher than that of hydrochloric acid.

    4. Compound X dissolves in water will give a colourless solution. The colour of this solution will become brown after

    bubbling chlorine gas to it. Can you conclude what compound X is composed of? (2 marks)

    2+2+ Since X dissolves in water to give a colourless solution, so X does not contain coloured ions such as Fe or Cu.

     It will be oxidized by chlorine to give a brown solution. So it is most likely to be an iodide. Iodide can be oxidized by

    chlorine to form iodine which is brown in colour.

5. Sodium chromate (NaCrO) dissolves in water to give a yellow solution. The following reaction will occur when adding 24

    dilute hydrochloric acid to it.

    +2-2-2CrO(aq) + 2H(aq) ? CrO(aq) + HO(l) 4272

     (a) What can be observed after the reaction? (1 mark) the solution changes from yellow to orange.

    (b) Is this reaction a redox reaction? Explain your answer.(1 mark)

     No. It is because there are no changes in the oxidation numbers of all the elements involved.

6. (a) What is anodization of aluminium? (2 marks)

    Use aluminium as anode to electrolyze dilute sulphuric acid. The oxygen formed on the surface aluminium will react

    with it to form aluminium oxide. The formation of aluminium oxide on the surface of aluminium by this method is

    called anodization of aluminium.

     (c) What is the position of the amount of aluminium in the earth crust as compare with other elements? (1 mark)



    If X is zinc, Y is graphite and Z is copper(II) nitrate solution in the set-up shown above, what is the direction of electron

    flow in the external circuit? (1 mark) The electrons flow from zinc to copper.

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    8. What catalysts should be used to catalyse the following conversions? (4 marks)

     (a) cracking of hydrocarbon unglazed porcelain (b)hydration of ethene to ethanol phosphoric acid

    (c) fermentation of glucose to ethanol yeast (d)convert sulphur dioxide to sulphur trioxide vanadium(V) oxide

    9. Write an equation for the reaction of sodium hydroxide solution with each of the following solutions. (3 marks)

     (a) ammonium chloride solution NHCl + NaOH; NaCl + NH + HO 432

    2+(b) copper(II) nitrate solution Cu + 2 OH ; Cu(OH) (aq)(aq)2(s)

    2+(c) zinc sulphate solution Zn + 2 OH Zn(OH) (aq)(aq)2(s)

10. Ammonium dichromate ((NH)CrO) will decompose to chromium(III) oxide, water and nitrogen after heating. What 4227

    mass of water will be formed after complete decomposition of 126 g ammonium dichromate?

    R.A.M.: H=1.0, N=14.0, O=16.0, Cr=52.0(3 marks)

     All the hydrogen atom in ammonium dichromate will become water after decomposition. So 1 mole of ammonium

    dichromate will form 4 mole of water.

     No. of mole of water formed = no. of mole of ammonium dichromate x 4

     = 126 / (18x2+52x2+16x7) x 4 = 0.5 mole

     mass of water formed = 0.5 x 18 = 3.6 g

    11. Will gas be formed after heating copper with the following solutions? Name the gas if the result is positive. (2 marks)

     (a) dilute nitric acid Yes. Nitrogen monoxide (b) dilute hydrochloric acid No

    (c) dilute sulphuric acid No (d) concentrated sulphuric acid Yes. Sulphur dioxide

12. Precipitate will be formed in a kettle after prolong using it to boil hard water. The precipitate is mainly metal carbonates.

    What chemical can be used to remove it? (1 mark)

     Dilute hydrochloric acid

    13. How to get hydrated copper(II) sulphate crystal from copper(II) sulphate solution? (1 mark)

     By crystallization.

    14. A piece of copper strip will dissolve gradually in a solution of compound X. What X may be? ( 1 mark)

     Silver nitrate

15. State two uses of aluminium. (2 marks)

     To make the body of aircraft. To make soft drink can.

    16. Explain why lithium chloride conducts electricity in liquid state but not in solid state. (1 mark)

     The ions in lithium chloride are not mobile in solid state. The ions become mobile in liquid state.

    17. Starch is a kind of carbohydrate and it is also a natural occurring polymer. It forms a black solid when reacts with

    concentrated sulphuric acid. Name the reaction. (1 mark) Dehydration

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18. The following is a simple flow diagram of contact process:

    SO+ X reaction chamber absorption tower absorbed by Y in the absorption tower Z 2

     Name X, Y and Z. X: oxygen Y: concentrated sulphuric acid Z: oleum (3 marks)

    19. Describe four methods to distinguish iron(II) sulphate and iron(III) sulphate solutions. (4 marks)

     1. Add sodium hydroxide solution to the two solutions. Iron(II) sulphate will form a green ppt while iron(III) sulphate will

    form a brown ppt.

     2. Add aqueous ammonia to the two solutions. Iron(II) sulphate will form a green ppt while iron(III) sulphate will form a

    brown ppt.

    3 3. Add a few cm of acidified potassium permanganate solution to the two solutions. Iron(II) sulphate will decolourize the

    purple solution while iron(III) sulphate will not.

     4. Observe the colours of the two solutions. Iron(II) sulphate solution is green while iron(III) sulphate solution is pale


    20. A student heated a mixture of fat and sodium hydroxide solution for a certain time. Then it was added to a beaker that

    contained saturated sodium chloride solution. Some white solids were formed.

(1) Name the reaction of fat and sodium hydroxide. Saponification (1 mark)

(2) What is the white solid formed? Soap (1 mark)

    (3) Name another substance formed. Glycerol (1 mark)

21. Name a suitable drying agent for drying chlorine. Concentrated sulphuric acid (1 mark)

22. Name a suitable drying agent for drying sulphur dioxide. Concentrated sulphuric acid (1 mark)

23. State two major uses of sulphuric acid. To make fertilizer / detergent / dye / synthetic fibre / paint (2 marks)

24. The structures of ethene and ethyne are: CH=CH HCCH 22

     ethene ethyne

     (1) Explain why they are both called unsaturated hydrocarbons. (1 mark)

     Ethene has C=C double bond while ethyne has CC triple bond

    (2) Ethyne burns with more dark smoke than that of ethene. Why? (1 mark)

     Ethyne has a higher percentage of carbon.

    25. Bubble sulphur dioxide to water will form a colourless solution.

     1 This solution is a better conductor of electricity than water. Why? (2 marks)

    + Sulphur dioxide dissolves in water to form sulphurous acid. Sulphurous acid will ionize partly to form H ,

    -2-HSO and SO. The mobile ions formed increase the conductivity of water. 33

     2 This solution can change iron(III) sulphate solution from yellow to green. Why? (2 marks)

     Sulphur dioxide is a reducing agent that reduces iron(III) to iron(II). So the solution changes from yellow to


     3 This solution can change bromine water from orange to colourless. Why? (2 marks)

     Sulphur dioxide is a reducing agent that reduces bromine to bromide. So the solution changes from orange to



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