1. 1
   An oil refinery separates crude oil into different fractions using fractional distillation, heating the crude oil and collecting the fractions that condense at different heights in a tall column. Most of the hydrocarbons in crude oil are alkanes of different chain lengths.

   (a)

   What is crude oil primarily a mixture of?

   [1 mark]

   • AHydrocarbon molecules made only of hydrogen and carbon atoms
   • BPure water and dissolved metal salts
   • CA single pure compound with one fixed boiling point
   • DAmino acids and proteins

   (b)

   As the chain length (molecular size) of the alkane hydrocarbons in crude oil increases, what generally happens to their boiling point?

   [1 mark]

   • AThe boiling point decreases
   • BThe boiling point increases
   • CThe boiling point stays exactly the same
   • DThe boiling point becomes negative

   (c)

   Explain how fractional distillation is able to separate crude oil into fractions containing hydrocarbons of similar chain length and boiling point.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fuel supplier compares two fractions from crude oil: petrol, made of short-chain hydrocarbons, and heavy fuel oil, made of long-chain hydrocarbons, both stored in tanks at the same temperature.

   (a)

   Which fraction is more viscous (thicker and less easily poured)?

   [1 mark]

   • ABoth fractions have exactly the same viscosity
   • BPetrol, because its shorter chains give it a higher viscosity
   • CHeavy fuel oil, because its longer chains give it a higher viscosity
   • DViscosity does not depend on hydrocarbon chain length at all

   (b)

   Which of the two fuels, petrol or heavy fuel oil, is more flammable (ignites more easily)?

   [1 mark]

   • ANeither fuel is flammable at all
   • BHeavy fuel oil, because longer-chain hydrocarbons are generally more flammable
   • CBoth fuels are exactly equally flammable
   • DPetrol, because shorter-chain hydrocarbons are generally more flammable

   (c)

   Propane (C3H8) is a short-chain alkane found in the refinery gases (LPG) fraction. Write a balanced symbol equation for the complete combustion of propane in oxygen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A petrochemical plant uses catalytic cracking to break down decane (C10H22), a long-chain alkane with limited demand as a fuel, into smaller, more useful hydrocarbon molecules, including one alkene product.

   (a)

   Describe the general conditions used in catalytic cracking and the general types of product formed.

   [3 marks]

   (b)

   One cracking reaction produces octane (C8H18) as one product, alongside a second, smaller hydrocarbon product. Balance the equation C10H22 -> C8H18 + ? to find the formula of the second product, and describe a simple chemical test that could show whether this second product is an alkene.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An oil refinery manager is deciding whether to invest in a catalytic cracking unit, and is also considering the longer-term implications of the refinery's continued reliance on crude oil as its raw material.

   (a)

   Fractional distillation of the refinery's crude oil naturally produces far more long-chain fractions, such as heavy fuel oil, than short-chain fractions such as petrol, while customer demand is much higher for short-chain fuels. Explain why the refinery would use cracking to address this situation, referring to the general conditions and products of cracking.

   [6 marks]

   (b)

   Evaluate the extent to which modern life depends on the uses of hydrocarbons obtained from crude oil, and discuss the implications of crude oil being a finite resource.

   [6 marks]

   Total for question 4: 12 marks

End of questions