Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
How the physical properties of hydrocarbons change with molecule size
19 practice questions
Practice questions
11–19 of 19
Question 11
3 marks · Normal
Answer and see the solution →The boiling points of fractions from crude oil are related to the number of carbon atoms in their molecules.
Boiling points of two hydrocarbon fractions Fraction Typical Number of Carbon Atoms Boiling Point (°C) Gasoline (petrol) 8 110 Diesel 15 260 (a)[3 marks]Calculate the increase in boiling point per additional carbon atom between these two fractions.
Question 12
3 marks · Normal
Answer and see the solution →Explain why hydrocarbons with larger molecules burn less easily than hydrocarbons with smaller molecules.
Question 13
4 marks · Normal
Answer and see the solution →The table below shows properties of different hydrocarbon fractions obtained from crude oil.
Properties of hydrocarbon fractions Fraction Approx. number of C atoms Boiling point (°C) Colour Flow (viscosity) Ease of burning Refinery gas 3 -20 Colourless Very runny Burns very easily Kerosene 12 200 Light yellow Fairly runny Burns easily Fuel oil 20 340 Dark brown Thick Does not burn easily (a)[2 marks]Which fraction is the most viscous? Give a reason for your answer.
(b)[2 marks]State how boiling point, colour, and ease of burning change as you go from refinery gas to fuel oil.
Question 14
1 mark · Normal
Answer and check →Which statement about hydrocarbon fractions with small molecules is correct?
- A.They have high boiling points and are very viscous.
- B.They are dark in colour and burn with difficulty.
- C.They are very volatile and burn easily.
- D.They are thick liquids and flow slowly.
Question 15
2 marks · Normal
Answer and see the solution →State two ways in which refinery gas differs in physical properties from bitumen, another fraction from crude oil.
Question 16
4 marks · Normal
Answer and see the solution →Hydrocarbon fractions are collected at different heights in a fractionating column, depending on their boiling points.
(a)[1 mark]State what is meant by the volatility of a liquid.
(b)[2 marks]Explain why the fraction collected at the top of the column is more volatile than the one at the bottom.
(c)[1 mark]Give one use each for the top fraction and the bottom fraction.
Question 17
2 marks · Hard
Answer and see the solution →State two changes in the physical properties of hydrocarbon fractions as the number of carbon atoms in their molecules increases.
Question 18
5 marks · Hard
Answer and see the solution →Crude oil is separated into fractions by fractional distillation. Two fractions, A and B, are collected at different heights in the fractionating column.
(a)[2 marks]Fraction A consists of large hydrocarbon molecules, while fraction B consists of small hydrocarbon molecules. State which fraction is collected higher up the column. Give a reason for your answer.
(b)[2 marks]Describe how the physical properties (boiling point and viscosity) of fraction A compare to those of fraction B.
(c)[1 mark]Suggest one use for fraction B, based on its physical properties.
Question 19
2 marks · Hard
Answer and see the solution →Explain why hydrocarbons with larger molecules are less useful as fuels than those with smaller molecules.