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Chemistry 2006 WAEC Past Questions

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31

(a) A solution of CuSO\(_4\) was electrolyzed between pure copper electrodes and the following results were obtained:

Mass of copper anode before experiment = 7.20 g

Mass of copper anode after experiment = 4.00 g

Mass of copper cathode before experiment = 5.75 g

From the information provided,

(i) calculate the mass of the cathode, after the experiment.

(ii) write an equation for the reaction at the I. anode, II. cathode.

(iii) state whether the colour of the solution would change during the electrolysis. Give a reason for your answer.

(iv) if the electrolysis was carried out for 1 hour 20 minutes with a current of 2.0 amperes, determine the value of the Faraday.

 

(b) Consider the reaction represented by the following equation:

MnO\(^-_4\) + I\(^-\) + H\(^+\)  \(\to\) I\(_2\) + H\(_2\)O + Mn\(^{2+}\) 

Write balanced half equation for the (i) oxidation reaction, (ii) reduction reaction.

 

(c)(i) Describe briefly how tin can be extracted from its ore.

(ii) State one use of tin.

(iii) Mention one property that makes tin suitable for the use stated in (c)(ii)

 

(d)(i) What is meant by the term pollution?

(ii) Explain why it is dangerous to run a generator in a closed room.

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32

(a)(i) Draw and label a diagram to illustrate the preparation and collection of dry chlorine gas in the laboratory.

(ii) List two uses of chlorine.

 

(b)(i) Explain why river water flowing through an industrial town may be unsafe for drinking.

(ii) State the use of each of the following substances in water treatment: I. Sand, II. Chlorine, III. Calcium oxide, IV. Alum

 

(c)Consider the reaction represented by the following equation:

2Na\(_2\)CI\(_{(s)}\) + H\(_2\)SO\(_{4(aq)}\) \(\to\) Na\(_2\)SO\(_{4(aq)}\) + 2HCI\(_{(g)}\)

Calculate the volume of HCI gas that can be obtained at s.t.p. from 5.85 g of sodium chloride. [H = 1, Na = 23, CI = 35.5, Molar volume a 22.4 dm\(^3\) at s.t.p]

(d) Give one example in each case of a (i) metal that is a liquid at room temperature. (ii) non-metal that is a iiquid at room temperature, (iii) gas at room temperature that is monatomic.

(e) State two differences between metals and nom metals with respect to their: (i) physical properties; (ii) chemical properties.

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33

(a)(i) Draw the energy profile diagram for the reaction

H\(_{2(g)}\) + I\(_{2(g)}\) ---> 2HI\(_{(g)}\)   \(\Delta\) = —13 kJmol\(^3\)

(ii) If the concentration of HI increases from 0 to 0.001 mol dm\(^3}\) in 50 seconds, what is the rate of the reaction?

 

(b) State the type of salt represented by each of the following compounds:

(i) K\(_4\)Fe(CN)\(_6\) (ii) (NH\(_4\))\(_2\)Fe(SO\(_4\))\(_2\)6H\(_2\)O (iii) Mg(OH)NO\(_3\) (iv) NaH\(_2\)PO\(_4\).

 

(c) Explain, giving equations, the following observation: When carbon (IV) oxide is passed into lime water, it turns milky initially but turns clear with excess carbon (IV) oxide.

 

(d)(i) Give one use for each of the following compounds: CaCO\(_3\), CaSO\(_4\), NaHCO\(_3\).

 

(ii) State a drying agent for each of the following gases: i. NH\(_3\), II. HCI Ill. SO\(_4\).

 

(iii) Write an equation to illustrate the reaction of ammonia as a reducing agent.

 

(e) An industrial raw material has the following composition by mass:

Iron = 28.1%

Chlorine = 35.7%

Water of crystallization = 36.2%

Calculate the formula for the material. [ H = 1, 0 = 16, Cl = 35.5, Fe = 56 ].

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34

(a) Consider the following compounds: MnO\(_2\), NaHCO\(_3\), Na\(_2\)CO\(_3\), NH\(_4\)CI cnd Pb(NO\(_3\))\(_2\) Select the compound(s) which;

(i) has a black colour

(ii) is a basic oxide:

(ii) sublime on heating

(iv) dissolves in water to give a solution of pH less than 7.

 

(b) State the colour of each af the following aqueous Solutions:

(i) Calcium hydroxide;

(ii) iron (III) trioxonitrate (V):

(ii) Copper (II) tetraoxosulphate (VI);

(iv) Poassium heptaoxodichromate (VI).

 

(c) Give one example of a neutral oxide which is a colourless liquid at room temperature.

(d) Draw and label a diagram for a set-up that can be used for the separation of two immiscible liquids

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35

Credit will be given for strict adherence to the instructions, for observations precisely recorded and accurate inferences. All tests, observations and inferences must be clearly entered in your als book, in ink, at the time they are made.

C is a mixture of an inorganic and organic compounds. Carry out the following exercises on C: Record your.observations and identity any gases evolved. State the conclusion you draw from the result of each test.

(a) Put all of C into a beaker and add 10 cm\(^3\) of distilled water: Stir the mixture thoroughly and filter. Keep both the filtrate and residue.

(b)(i) Test the filtrate with litmus paper.

(ii) To about 2 cm\(^3\) of the filtrate, add BaCI\(_{2(aq)}\) followed by dilute HCI:

(iii) To another 2 cm\(^3\) portion of the filtrate add NaOH and heat.

(c) Transfer the residue into a boiling tube and add few drops of iodine solution

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