2023 WAEC CHEMISTRY PRACTICAL ALTERNATIVE A ANSWERS | 18TH MAY, 2023
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WAEC Chemistry Practical Specimen 2023 – Apparatus
1. Great care should be taken to ensure that the information given in items 2 and 3 below does not reach the candidate either directly or indirectly before the examination.
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 50 cm3 capacity;
(b) One pipette, either 20 cm3 or 25 cm3. (All candidates at one centre 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 labelled;
(i) Dilute sodium hydroxide solution;
(ii) Dilute hydrochloric acid;
(iii) Dilute trioxonitrate
(V) acid;
(iv) Silver trioxonitrate
(v) Acidified potassium dichromate solution;
(vi) Aqueous ammonia;
(vii) Lime water;
(viii) Red and blue litmus paper
(ix) Dilute tetraoxosulphate (VI) acid;
(x) Fehlings solution A & B.
(e) Spatula;
(f) Filtration apparatus;
(g) One beaker
(h) One boiling tube;
(i) Four test tubes;
(j) Methyl orange as indicator;
(k) Glass rod;
(1) Wash bottle containing distilled/deionized water;
(m) Burning splint;
(n) Watch glass;
(o) Bunsen burner/source of heat;
(p) Droppers;
(q) Mathematical table/calculator.
3. Each candidate should be supplied with the following, where ‘n’ is the candidate’s serial number
(a) 150 cm3 of a solution of HCI in a corked flask or bottle labelled ‘An’. These should all be the same containing 8.5 cm3 of concentrated HCI per dm3 of solution.
(b) 150 cm3 of Na2CO3.10 H20 in a cork flask or bottle labelled ‘Bn’. These should be the same containing 5.0 g of the hydrated per dm3 of solution.(c) One spatulaful of glucose in a specimen bottle labelled ‘Cn’. This must be the same for all candidates.
(d) One spatulaful of zinc oxide powder in a specimen bottle labelled ‘Dn’. This must be same for all candidate.
4. In all cases, more materials may be issued if required
5. The actual concentrations of A and B must be stated on the Supervisors report form.
The candidates will assume that the concentrations are exactly as stated in the question paper
6. It should be noted that schools are not allowed to amend the information provided on the question paper or substitute any substance/solution for those specified in these instructions.
2023 WAEC CHEMISTRY PRACTICAL QUESTIONS
*COMPLETE NUMBER 3*
3a.
When a few drops of NaOH solution are added to a 2 cm³ solution of Pb(NO3)2 (lead nitrate), the following observation would be made:
A white precipitate of lead(II) hydroxide (Pb(OH)2) would form. Lead(II) hydroxide is insoluble in water and appears as a white solid. The reaction can be represented as:
Pb(NO3)2 + 2NaOH -> Pb(OH)2 + 2NaNO3
The formation of a white precipitate indicates the presence of lead(II) ions in the solution, and the reaction between Pb(NO3)2 and NaOH results in the formation of lead(II) hydroxide.
3aii.
When a few drops of NaOH solution are added to a 2 cm³ solution of Fe2(SO4)3 (iron(III) sulfate), the following observation would be made:
A reddish-brown precipitate of iron(III) hydroxide (Fe(OH)3) would form. Iron(III) hydroxide is insoluble in water and appears as a reddish-brown solid. The reaction can be represented as:
Fe2(SO4)3 + 6NaOH -> 2Fe(OH)3 + 3Na2SO4
The formation of a reddish-brown precipitate indicates the presence of iron(III) ions in the solution, and the reaction between Fe2(SO4)3 and NaOH results in the formation of iron(III) hydroxide.
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3b
To determine the melting point of benzoic acid in the laboratory, the following procedure can be followed:
1. Obtain a small amount of benzoic acid sample. Ensure that the sample is dry and free from any impurities.
2. Set up a melting point apparatus, such as a melting point apparatus or a capillary tube.
3. Clean and dry a capillary tube, which is a thin glass tube used to hold the sample. Fill the capillary tube with a small amount of powdered benzoic acid, ensuring it is compact and uniform.
4. Insert the capillary tube into the melting point apparatus, making sure it is secure.
5. Gradually heat the melting point apparatus while observing the benzoic acid sample through the magnifying lens.
6. As the temperature rises, observe the sample for any signs of melting. Initially, the powdered benzoic acid will remain solid, but at a specific temperature, the sample will start to melt and form a liquid phase.
7. Note the temperature at which the first signs of melting are observed.
8. Repeat the experiment at least two more times using fresh samples to ensure the accuracy and consistency of the obtained melting point values.
By following this procedure, the melting point of benzoic acid can be determined in the laboratory.
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