WASSCE WAEC Chemistry Practical Questions

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ESSAY [100 MARKS]

Answer four questions in all: question 1 in Section A and three questions from Section B. All questions carry equal marks.

No marks will be awarded for answering questions not specified for your own country. Credit will be given for clarity of expression and orderly presentation of materials.

SECTION A

Answer all the questions in this section.

1. (a) (i) Define an acid according to the Lewis concept.

(ii) Give one example of a Lewis acid. [3 marks]

(b) Explain salting out in soap preparation. [2 marks]

(c) State the reagent and condition necessary for the following conversion:

II C ≡ C H ► Ag C ≡ C Ag [2 marks]

(d) What is the percentage abundance of an isotope? [2 marks]

(e) (i) Why does the element with atomic number 18 not have on oxide?

(ii) Explain why chlorine (I) oxide has a low melting point. [3 marks]

(f) Describe a test to distinguish between concentrated HNO3 and concentrated H2SO4 [3 marks]

(g) State two differences between an electrochemical cell and an electrolytic cell. [3 marks]

(h) How does the trend in ionization energy affect the reactivity of group 1 elements? [3 marks]

(i) Define the term molecular formula. [2 marks]

(j) (i) Slate which of the gases 11, and NH, would deviate more from ideal behaviour.

(ii) Give reasons for the answer stated in 1(j) ( i) [3 marks]

SECTION B

Answer any three questions in this section. FOR ALL CANDIDATES

2. (a) (i) Define the first ionization energy of an element

(ii) Consider die following table and use it to answer the question that follows.

Explain briefly why the first ionization/energy of B is less than that of Be despite the fact that the atomic number of B is greater than that of Be [8 marks]

(b) When Titanium chloride was electrolyzed by passing 0.12 A current through the solution for 500 seconds. 0.015g of titanium was deposited. What is the charge on the titanium ion?

[

= 96500 C, Ti = 48.0) [6 marks]

(C) (i) Aluminium can be obtained by the application of electrolysis. State the electrolyte which yields aluminium on electrolysis.

(ii) Name two major factors which would favour the sitting of an aluminium smelter in a country. [6 marks]

(d) (i) Define the term paramagnetism

(ii) Consider the following ions:

24 24

(I) Deduce the number of unpaired electrons in each of the ions.

(II) State which of the ions will have a greater power of paramagnetism.

(Ill) Give a reason for the answer stated in 2(d)(ii) (II). [7 marks]

3. (a) (i) Define the term Avogadro's number

(ii) If 2.30g of an oxide of nitrogen. , contains 3.01 × 1022 molecules, calculate the molar mass of

(iii) Deduce the formula of

[NA = 6.02 × 1023, N = 14.0. O = 16.0] [6 marks]

(b) (i) Describe briefly what happens when each of the following substances are added to water

(i) CCI4

(ii) SiCI4

(iii) Explain briefly why the reactions in 3(b)(i)(I) and 3(b)(i)(II) are different [6 marks]

(c) Study the diagram below and answer the questions that follow

5.

(i) What is the set-up used for?

(ii) Mention two compounds that could be used as electrolytes in the cell.

(iii) Write a half-cell equation for the reaction at the anode.

(iv) Calculate the electrochemical equivalent of copper if the cathode gained mass of 3.2g when 50 amperes of current was passed for 3 mins 13 seconds. [10 marks]

(a) Describe the observation that would be made when:

(i) sulphur is heated from room temperature till 119°C

(ii) 50% trioxomate (V) acid acts on copper tunings. [6 marks]

(b) (i) State two gaseous pollutants that can be generated by burning coal

(ii) What gas is responsible for most of the explosions in coal mines?

(iii) The mining of coal lead to environmental pollution. State two environmental effects of the mining activity

(iv) Explain briefly why coal bums more easily when it is in pieces than in lump form.

(v) Name the non-volatile residue after the destructive distillation of coal. [6 marks]

(c) (i) Describe a chemical test for water.

(ii) State the effect of:

(I) boiling a temporary hard water,

(II) adding sodium trioxocarbonate (IV) crystals to permanent hard water.

(iii) Write an equation for the process in 5(c) (ii) (I).

(d) With the aid of a labelled diagram, describe briefly the laboratory preparation of oxygen gas

.

WAEC CHEMISTRY PRACTICAL SPECIMEN:

(1)

INSTRUCTIONS

(2)

In addition to the fittings and reagents normally found in a chemistry laboratory, the following apparatus and materials will be required by each candidate.

(a) One Burette of 50cm3 of capacity

(b) One pipette, either 20cm3 or 25cm3 (All candidates at one center must use pipettes of the same volume, these should be clean and free from grease).

(c) The usual apparatus for titration

(d) The usual apparatus and reagents for qualitative work including the following with all reagents appropriately labeled:

(i) 10% dilute sodium hydroxide solution

(ii) dilute hydrochloric acid

(iii) dilute trioxonitrate(v) acid

(iv) silver trioxonitrate(v) acid

(v) acidified potassium dichromate solution

(vi) aqueous ammonia

(vii) lime water

(viii) red and blue litmus paper

(ix) dilute tetraoxosulphate(vi)

(x) aqueous barium chloride

(e) Spatula

(f) Filtration apparatus,

(g) One beaker

(h) One boiling tube

(i) Four test tubes

(j) Starch solution indicator

(k) Glass rod

(l) Wash bottle containing distilled/deionized water,

(m) Burning splint,

(n) Watch glass

(o) Bunsen Burner/source of heat

(p) Droppers .

(3)

(a) 150cm3 of iodine solution in a corked flask or bottle labeled ‘An’. These should all be the same containing 25.4g of I2 in 6.0g kl per dm3 of solution.

(b) 150cm3 of sodium thiosulphate pentahydrate solution in a corked flask or bottle labeled ‘Bn’. These should all be the same containing 24.82g of Na2S2O3 per dm3 of solution.

(c) One spatulaful of ammonium ferrous sulphate, (NH4)2Fe(SO4)2.6H2 O in a specimen bottle labeled ‘Cn’. This must be the same for all candidates.

Answer All questions

All your burette rending (initial and final) as well as the size of your pipette must be recorded but no account of experimental procedure is required.

All calculations must he done in this booklet

1. A is an aqueous solution of Iodine. B is 0.100 mol dm-3 sodium trioxothiosulphate (II).

(a) Put B into the burette. Pipette 20.0 cm3 or 25.0cm3 of A into a conical flask. Add B front the burette until the reddish-brown colour fades to pale yellow, then add a few drops of starch indicator to obtain a dark blue solution. Continue adding B slowly from the burette until one drop of B causes the blue colour to disappear, leaving a colourless solution.

Repeat the titration to obtain concordant titre values.

Tabulate your results and calculate the average volume of B used.

The equation for the reaction is:

2Na2S2O3(aq) + l2(aq) > Na2S4O6(aq) + 2Nal(aq)

(b) From your results and the information provided, calculate the:

(i) Concentration in mol dm-3 of iodine in A;

(ii) mass in grammes of iodine in 1.00dm3 of A (I=127.0]

[17 marks]

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

2. C contains two cations and one anion.

(a) Dissolve all of C in about 10cm3 of distilled water. Carry out the following exercises on portion of the resulting solution.

(i) To about 2 cm3 of the solution, add NaOH(aq) in drops then in excess. Warm gently the resulting mixture.

(ii) To about 2 cm3 of the solution, add BaCl2(aq) followed by excess dilute HCL

(b) From your results identify the cations and anion in the sample.

[18 marks]

(a) Describe one chemical test to distinguish between carbon (IV) oxide and sulphur (IV) oxide [3 marks]

(b) (i) State the Laboratory method of collection of each of the following gases:

(I) H2

(II) NH3

(III) HCl

(ii) Give a reason for each of the answer stated in 3(b)(i) [6 marks]

(c) State the method used in separating each of the following mixtures:

(i) two miscible liquids;

(ii) soluble salt and insoluble salt [3 marks]

(d) Explain briefly why a solution of KCI does not give off a gas when mixed with NaHCO3 solution, but a solution of AlCl3 does. [3 marks]