Waec 2022 chemistry practicals questions and answers
(1a)
Volume of pipette used, VA = 25.0cm³
[TABULATE]
Burette Reading | Rough titre | 1st titre | 2nd titre |
Final Burette reading (cm³) | 25.60 | 32.80 | 26.40
Initial Burette reading (cm³) | 1.20 | 8.70 | 2.30
Volume of Na₂S₂O₃ used | 24.40 | 24.10 | 24.10
Average burette reading = (24.10 + 24.10)/2
Average volume of Na₂S₂O₃ used = 24.10cm³
VB = 24.10cm³
(1bi)
Given: CB = 0.1mol/dm³
VB = 24.10cm³
VA = 25.0cm³
CA =?
From equation nA/nB = 1/2
.: Using (CABA)/CBVB = (nA)/nB
(CA x 25)/(0.1×24.10) = 1/2
CA = (0.1×24.10)/(25×2)
CA = 0.0482mol/dm³
.: Concentration of iodine in A = 0.0482mol/dm³
(1bii)
Mass in gramms of iodine in 1dm³ of A = Molarity × Molar mass of iodine
= 0.0482×127(2)
= 12.2428g/dm³
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(2a)
[TABULATE]
=TEST=
C + Distilled water
=OBSERVATION=
It dissolves completely to give a light green solution.
=INFERENCE=
Soluble salt.
(2ai)
=TEST=
Solution C + NaOH in drops and in excess + Heat gently
=OBSERVATION=
A dirty green precipitate is formed which remains insoluble in excess.
Effervescence occurs in which a colourless gas with a pungent smell which turns red litmus blue is given off.
=INFERENCE=
Fe²⁺ is present.
NH₃ gas form.
NH₄⁺ is present.
(2aii)
=TEST=
Solution + BaCl₂ + dilute HCL in excess
=OBSERVATION=
A white precipitate is formed.
The white precipitate remains insoluble and gives a white dense forms
=INFERENCE=
SO₄²⁻, CO₃²⁻, SO₃²⁻, is present.
SO₄²⁻ confirmed.
(2b)
Cations → Fe²⁺ and NH₄⁺
Anions → SO₄²⁻
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(3a)
Carbon (iv) oxide turns like water milky white while sulphur (iv) oxide does not
(3b)
(I) H₂: Downward displacement of air
(II) NH₃: Downward displacement of air
(III) HCL: Upward displacement of air
(3bii)
I – It is less dense than air
II – It is less dense than air
III – It is denser than air
(3c)
(i) Distillation
(ii) Filtration followed by evaporation to dryness
(3d)
This is because KCl react with NaHCO₃ to form two salts
Completed
IMAGE ANSWERS
(No1)
(No2)
(3a)
(3bi)
(I) H2 ; downward displacement of water
(II) NH3; downward displacement of air
(III) HCL; upward displacement of air
(3bii)
(I) Hydrogen gas(H2) is collected by the downward displacement of water because It is insoluble in water and It form an explosive mixture with air.
(II) Ammonia gas(NH3) is collected by downward displacement of air because it is lighter than air
(III) HCl gas is collected by upward displacement of air because it is 1.28 times heavier than air.
(3c)
(i) Distillation
(ii) Filtration followed by evaporation to dryness
(3d)
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WAEC 2022 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)2.6H2O in a specimen bottle labeled ‘Cn’.
This must be the same for all candidates.
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