Chemistry 2007 Jamb Examination
Question 1
Hydrogen is usually prepared with dilute HCl or H₂SO₄.
HNO₃ is not used because it is a strong oxidizing agent, converting the liberated hydrogen into water:
\[ 2HNO₃ + Zn → Zn(NO₃)₂ + H₂ \]
Then: \[ 2H₂ + O₂ → 2H₂O \]
Thus, hydrogen is not collected. Correct option A.
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Question 2
The striking surface of matches contains red phosphorus, while the matchstick head contains antimony (III) sulfide and sulphur.
Thus, sulphur is directly involved in match production. Correct option D.
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Question 3
On heating, CaO reacts with carbon to form calcium carbide:
\[ CaO + 3C → CaC₂ + CO \]
Thus, the product is carbide. Correct option A.
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Question 4
The reaction is:
CaCO3 + 2HCl → CaCl2 + H2O + CO2
The gas (CO2) is colourless, odourless and turns limewater milky:
Ca(OH)2 + CO2 → CaCO3 ↓ + H2O
So the correct answer is trioxocarbonate (IV). Option C.
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Question 5
Soft solder is an alloy of lead (Pb) and tin (Sn), usually in about 50:50 ratio.
It has a low melting point and is used in plumbing and electronics.
Correct option A.
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Question 6
Rust is hydrated iron (III) oxide, generally written as Fe₂O₃·3H₂O.
It forms when iron reacts with oxygen and water. Correct option C.
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Question 7
Reaction rate generally increases with higher temperature (more energetic collisions) and higher concentration (more frequent collisions).
Thus, the greatest increase is from both together. Correct option D.
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Question 8
Tincture of iodine is a solution of iodine in ethanol with some water, used as an antiseptic.
Correct option A.
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Question 9
If Cu²⁺ is removed (by precipitation as CuS), the equilibrium shifts left (Le Chatelier’s principle). This releases NH₃ back into solution, increasing free NH₃.
So, more NH₃(g) remains. Correct option B.
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Question 10
Copper and silver resist corrosion because they are not easily oxidized. This makes them durable for coinage.
Correct option D.
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