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WAEC WASSCE Chemistry 2012 past questions and answers

This 2012 WAEC WASSCE 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 2012 set with instant marking.

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Sample WAEC WASSCE Chemistry 2012 questions

1. A current of 2.00 A is passed through aqueous copper(II) sulfate for 96,500 s. What mass of copper is deposited? (F = 96,500 C mol-1; Cu = 63.5)
  1. 63.5 g
  2. 31.75 g
  3. 127 g
  4. 2.00 g

Answer: A. 63.5 g

The charge is 193,000 C, equivalent to 2 mol of electrons and therefore 1 mol of copper atoms, which has a mass of 63.5 g.

2. An iron pipeline is protected from corrosion by attaching blocks of magnesium to it. How does the magnesium protect the iron?
  1. It forms an impermeable oxide coating on the iron
  2. It oxidizes preferentially to the iron
  3. It neutralizes acids in the soil
  4. It prevents oxygen from dissolving in water

Answer: B. It oxidizes preferentially to the iron

Magnesium is more reactive than iron and acts as a sacrificial metal by losing electrons in preference to the iron.

3. Which observation provides a positive test for an alkene when bromine water is added in the absence of ultraviolet light?
  1. A blue-black colour appears
  2. A white precipitate forms
  3. The orange-brown colour disappears
  4. Effervescence occurs

Answer: C. The orange-brown colour disappears

An alkene adds bromine across its carbon-carbon double bond, decolourising the bromine water.

4. What is the molecular formula of the alkane that contains four carbon atoms?
  1. C4H8
  2. C4H6
  3. C4H12
  4. C4H10

Answer: D. C4H10

Alkanes have the general formula CnH2n+2, so for n = 4 the formula is C4H10.

5. What is the main organic product formed when ethanol reacts with ethanoic acid in the presence of concentrated sulfuric acid?
  1. Ethyl ethanoate
  2. Methylethanoate
  3. Ethanal
  4. Ethanamide

Answer: A. Ethyl ethanoate

Ethanol and ethanoic acid undergo esterification to form ethyl ethanoate and water.

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