Author Topic: CORRECT: 2024 WAEC CHEMISTRY PRACTICAL ANSWERS (ALT. B) (Read 1848 times)

MANDINHO · « **on:** June 20, 2024, 07:56:40 am »

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MANDINHO · « **Reply #1 on:** June 20, 2024, 11:27:32 am »

CHEMISTRY PRACTICAL ANSWERS

(1)

(1c)

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(2a)
Test: Add dil. HCl to F
Observation: Effervescence (bubbling) observed, clear solution formed
Gas evolved: CO₂
Conclusion: F is a carbonate or bicarbonate salt, reacting with acid to produce CO₂ gas.

(2bi)
Test: Add NaOH to the clear solution
Observation: White precipitate forms, dissolves in excess NaOH, no change on warming
Conclusion: The salt formed is likely CaCl₂ or MgCl₂, which forms a precipitate with NaOH that dissolves in excess NaOH.

(2bii)
Test: Add potassium hexacyanoferrate(II) solution
Observation: Blue precipitate forms
Conclusion: F contains Fe₃⁺ ions, which form a blue precipitate with potassium hexacyanoferrate(II) solution (Prussian blue).
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(3a)
(i)The salt solution was acidic in nature, as it reacted with sodium trioxocarbonate(IV) (sodium carbonate) to produce effervescence and a white precipitate.
(ii)The salt solution contained a calcium or magnesium ion, as these ions form a white precipitate with sodium carbonate.
(iii)The reaction was exothermic, as the test tube became warm, indicating the release of heat energy.

(3b)
(i) PbSO₄ (lead(II) sulfate) would not readily dissolve in water, as it is insoluble in water.
(ii) NaHCO₃ (sodium hydrogen carbonate) produces effervescence with dilute mineral acids, as it reacts with acids to produce carbon dioxide gas.
(iii) NH₄Cl (ammonium chloride) decomposes on heating, as it breaks down into ammonia and hydrogen chloride gases.
(iv) NaHCO₃ (sodium hydrogen carbonate) dissolves in water to form an alkaline solution, as it is a basic salt.
(v) NH₄Cl (ammonium chloride) sublimes on heating, as it changes directly from a solid to a gas without going through the liquid phase.

(3c)
(i) Use of Clean Apparatus: Ensure all glassware (burette, pipette, and conical flask) is clean to avoid contamination and ensure accurate results.
(ii) Proper Calibration and Reading of the Burette: Ensure the burette is properly calibrated and read the meniscus at eye level to avoid parallax errors.
(iii) Controlled Addition Near the Endpoint: As the endpoint is approached, add the titrant dropwise and swirl the flask to prevent overshooting the endpoint. This is critical with methyl orange, which changes color sharply.
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Author Topic: CORRECT: 2024 WAEC CHEMISTRY PRACTICAL ANSWERS (ALT. B) (Read 1848 times)

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CORRECT: 2024 WAEC CHEMISTRY PRACTICAL ANSWERS (ALT. B)

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