Hydrocarbons and alkanesIB MYP Chemistry: Subtopic test

1. 1
   A refinery in Rotterdam heats crude oil until most of it has vaporised and then feeds it into a tall fractionating column. The column is hot at the bottom and much cooler at the top. Different products are drawn off at different heights.

   (a)

   Which statement describes crude oil?

   [1 mark]

   • AA single compound containing carbon and hydrogen in a fixed ratio
   • BAn element made of carbon atoms only
   • CA mixture of many different hydrocarbons
   • DA mixture of ionic compounds dissolved in water

   (b)

   Compared with a fraction drawn off near the bottom of the column, a fraction drawn off near the top has molecules that are

   [1 mark]

   • Alonger, with higher boiling points
   • Bshorter, with lower boiling points
   • Clonger, with lower boiling points
   • Dshorter, with higher boiling points

   (c)

   Explain how fractional distillation separates the hydrocarbons in crude oil into fractions.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student is given the molecular formulae of a series of hydrocarbons: CH₄, C₂H₆, C₃H₈, C₄H₁₀ and C₅H₁₂.

   (a)

   Which is the general formula of the alkanes?

   [1 mark]

   • ACₙH₂ₙ
   • BCₙH₂ₙ₋₂
   • CCₙHₙ
   • DCₙH₂ₙ₊₂

   (b)

   Which name is given to the alkane with the molecular formula C₇H₁₆?

   [1 mark]

   • AHeptane
   • BHexane
   • CPentane
   • DOctane

   (c)

   Explain why propane, C₃H₈, is described as a saturated hydrocarbon.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Mexico City investigates what is produced when methane, the main gas in natural gas, burns in a Bunsen burner with the air hole open. She holds a cold, dry glass funnel above the flame and connects it by a tube to a boiling tube containing limewater.

   (a)

   Describe how the student could use the apparatus to show that burning methane produces both water and carbon dioxide.

   [3 marks]

   (b)

   Write the balanced symbol equation for the complete combustion of methane. When the student closes the air hole, the flame becomes yellow and a black solid forms on the cold glass. Explain this observation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The government of a fast-growing country in South-East Asia runs most of its vehicles on petrol and diesel from crude oil and generates much of its electricity in coal-fired power stations. It is considering building power stations that burn natural gas, which is mostly methane, and encouraging people to switch to electric vehicles.

   (a)

   Discuss the advantages and disadvantages of using petrol and diesel from crude oil as fuels for vehicles, and reach a justified conclusion.

   [6 marks]

   (b)

   Evaluate the proposal to replace coal-fired power stations with power stations that burn natural gas.

   [6 marks]

   Total for question 4: 12 marks

End of questions