Monday, 18th November 2024
Chemistry (Alternative to Practical)
2:00pm - 4:00pm

(1)

(2ai)

Observation: Dissolved to form a blue-green precipitate (ppt).

Inference: Presence of a transition metal salt

(2aii)

Observation: It turned blue litmus paper red.

Inference: The solution is acidic.

(2aiii)

Observation (drops of NaOH): A light blue gelatinous precipitate formed.

Inference: Presence of Cu²⁺ ions.

Observation (excess NaOH): The precipitate was insoluble in excess NaOH.

Inference: Cu²⁺ ions confirmed 

(2aiv)

Observation: A light blue precipitate formed.

Inference: Presence of Cu²⁺ ions.

(2av)

Observation: A black precipitate formed.

Inference: Presence of Cu²⁺ ions as CuS.

(2bi)

Observation: Acidic gas (HCl) was given off.

(2bii)

Inference: Confirms presence of Cl⁻ ions.

(2biii)

Inference: Presence of Cl⁻ ions.

(3ai)
(i) Litmus paper
(ii) Universal indicator paper
(iii) pH paper

(3aii)
Distilled water is free from impurities, dissolved salts, and ions (such as calcium, magnesium, or chloride ions) that may interfere with the reactions during analysis.

(3aiii)
(i) Smell or odor
(ii) Effects on litmus paper
(iii) Flammability 

(3bi)
Sodium trioxocarbonate (IV) (Na₂CO₃) functions as a base because it reacts with acids to neutralize them, forming a salt, water, and carbon dioxide gas.

(3bii)
Silver trioxonitrate (V) (AgNO₃) is light-sensitive and decomposes when exposed to light, releasing elemental silver and nitrogen oxides. Storing it in an amber-colored bottle protects it from light, preventing decomposition and maintaining its stability.

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