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JAMB UTME Chemistry 2023 past questions and answers

This 2023 JAMB UTME Chemistry set has 40 practice questions. Try these 5 free sample questions, tap a question to reveal the answer and explanation. Then practise the whole 2023 set with instant marking.

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Sample JAMB UTME Chemistry 2023 questions

1. Which product is formed when many ethene molecules undergo addition polymerization?
  1. Poly(propene)
  2. Poly(vinyl chloride)
  3. Poly(ethene)
  4. Nylon-6,6

Answer: C. Poly(ethene)

Ethene molecules add across their carbon-carbon double bonds to form the repeating chain in poly(ethene).

2. In the electrolytic extraction of aluminium, alumina is dissolved in molten cryolite mainly because cryolite
  1. lowers the melting point of the electrolyte and improves its conductivity.
  2. acts as the reducing agent for aluminium ions.
  3. prevents oxygen from forming at the anode.
  4. converts aluminium oxide into aluminium hydroxide.

Answer: A. lowers the melting point of the electrolyte and improves its conductivity.

Cryolite lowers the operating temperature and increases the electrical conductivity of the molten mixture.

3. For N2(g) + 3H2(g) ⇌ 2NH3(g), what is the effect of increasing pressure at constant temperature on the equilibrium yield of ammonia?
  1. It decreases because ammonia is more dense.
  2. It has no effect because the equation is balanced.
  3. It decreases because the forward reaction is exothermic.
  4. It increases because the product side has fewer gas molecules.

Answer: D. It increases because the product side has fewer gas molecules.

Higher pressure shifts the equilibrium toward the side with fewer gaseous molecules, which is the ammonia side.

4. In petroleum processing, cracking is used chiefly to convert
  1. short-chain alkanes into long-chain alkanes.
  2. large hydrocarbon molecules into smaller, more useful molecules.
  3. alkenes into saturated alcohols.
  4. crude oil into a single pure compound.

Answer: B. large hydrocarbon molecules into smaller, more useful molecules.

Cracking breaks long-chain hydrocarbons into shorter alkanes and alkenes that are in greater demand.

5. What volume of hydrogen at s.t.p. is produced when 5.6 g of iron reacts completely with excess dilute hydrochloric acid? (Fe = 56; molar gas volume at s.t.p. = 22.4 dm^3)
  1. 2.24 dm^3
  2. 1.12 dm^3
  3. 4.48 dm^3
  4. 11.2 dm^3

Answer: A. 2.24 dm^3

The equation Fe + 2HCl → FeCl2 + H2 gives 1:1 iron-to-hydrogen, so 5.6/56 = 0.10 mol H2 and its volume is 2.24 dm^3.

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