WAEC 2021 Chemistry Practical Question And Answer

WAEC 2021 Chemistry Practical Question And Answer

WAEC 2021 Chemistry Practical Questions And Answers

WAEC Chemistry 2021 Specimen.

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

(a) one burette of 50cm³ capacity.

(b) one pipette, either 20cm³ or 25cm³.

All candidates at a centre will 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 labelled.

(i) dilute sodium hydroxide solution.

(ii) dilute hydrochloric acid.

(iii) dilute trioxonitrate(v) acid.

(iv) silver trioxonitrate(v) solution.

(v) acidified potassium dichromate solution.

(vi) aqueous ammonia.

(vii) lime water.

(viii) red and blue litmus paper.

(ix) dilute tetraoxosulphate(vi) acid.

(e) Spatula.

(f) filtration apparatus.

(g) one beaker.

(h) one boiling tube.

(i) four test tubes.

(j) Methyl orange as an indicator.

(k) mathematical table/calculator.

(l) wash bottle containing distilled/deionized water.

(m) a burning splint.

(n) watch glass.

(o) bunsen burner/source of heat.

(p) droppers.

(3) Each candidate should be supplied with the following where n is the candidate’s serial number.

(a) 150cm³ of a solution of HCL, in a corked flask or bottle, labelled “An”. These should all be the same containing 9.0cm³ of concentrated HCL (about 60%) per dm³ of solution.

(b) 150cm³ of NaOH solution in a corked flask or bottle labelled “Bn”. These should all be the same containing 4.8g of NaOH per dm³ of solution.

(c) one spatula of a uniform mixture of CUSO4 and (NH4)2CO3 in a specimen bottle and corked immediately, and labelled “Cn”. The components of the mixture should be in the ratio 1 : 1 by mass.

(d) One spatula full of crystals of iodine in a specimen bottle labelled “Dn”. This must be the same for all candidates.

WAEC Chemistry Practical Questions

1. A is a solution of potassium tetraoxomanganate (VII). B is a solution of iron (II) Chloride containing 4.80 g of the salt in 250cm3 of solution.

(a) Put A into the burette. Pipette 20.0cm3 or 25.0 of B into a conical flask, add 20.0cm3 of H2SO4(aq)and titrate with A. repeat the titration to obtain concordant titire values.

Tabulate your results and calculate the average volume of A used. The equation of the reaction is: MnO–4(aq) + 5Fe2+(aq) + 8H+(aq) > Mn2+(aq) + 5Fe3+(aq) + 4H2O(I)

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

(i) concentration of B in moldm-3;

(ii) Concentration of A in moldm-3 (

iii) number of moles of Fe2+ in the volume of B pipetted [FeCI2 = 127 gmol-1].

Credit will be given for strict adherence to the illustrations for observations precisely and for accurate inferences.

All tests, observations and inferences must be clearly entered in the booklet in ink at the time they are made.

2. C and D are inorganic salts.

Carry out the following exercises on them.

Record your observations and identify any gas(es) evolved. State the conclusions and draw fromt the result of each test.

(a) Put all of C in a test tube and add about 5cm3 of distilled water. Shake thoroughly and test the resulting solution with litmus paper. Divide the solution into three portions.

(i) To the first portion, add NaOH(aq) in drops, then in excess.

(ii) To the second portion, add NH3(aq) in drops, then in excess.

(iii) To the third portion, add AgNO3(aq) followed by HCI(aq)

(b)(i) Put all of D in a test tube and add about 5cm3 of distilled water.

Shake thoroughly and feel the test tube. (ii) To about 2cm3 of the solution, add HCI(aq).

3. State the observations that would be made when each of the following reactions are carried out in the laboratory

(a) Addition of 2cm3 of bench H2SO4(aq) to 2cm3 of barrium chloride solution;

(b) Addition of 2cm3 of dilute hydrochloric acid to 1 g of powered iron(II) sulphide (FeS);

(c) Addition of 2cm3 of dilute hydrochloric acid to 1 g of iron filings and allowed to stand for sometime.

WAEC Chemistry Practical Answers

1. Equation of the reaction: MnO–4(aq) + 5Fe2+(aq) + 8H+(aq) > Mn2+(aq) + 5Fe3+(aq) + 4H2O(I)

3ai)
oxygen

(3c)

It turns blue litmus paper red.

3d
Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it. When water is present in a sample of copper(II) sulfate it turns blue.

This colour change can be used to detect the presence of water (or water vapour).

3c(i)
When exposed to light, silver chloride decomposes into gray metallic silver and chlorine. The light sensitivity of the silver chloride and other silver halides, such as silver bromide and silver iodide, forms the basis of the photographic process.

3bi()

Phenolphtalein is chosen because it changes color in a pH range between 8.3 – 10. It will appear pink in basic solutions and clear in acidic solutions. ..

3c(i)
When exposed to light, silver chloride decomposes into gray metallic silver and chlorine. The light sensitivity of the silver chloride and other silver halides, such as silver bromide and silver iodide, forms the basis of the photographic process.

3cii
The ammonia combines with silver ions to produce a complex ion called the diamminesilver(I) ion, [Ag(NH3)2]+. This is a reversible reaction, but the complex is very stable, and the position of equilibrium lies well to the right.

3d
Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it. When water is present in a sample of copper(II) sulfate it turns blue.

This colour change can be used to detect the presence of water (or water vapour).

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