The table gives information about some fractions obtained from petroleum. fraction boiling range / °C number of carbon atoms per molecule use refinery gas b...

This question is about reading a data table on petroleum fractions and the key definitions linked to crude oil. As the chain length rises, both boiling range and molecule size increase together, which is the pattern the table is designed to show.

(a) The fraction with the lowest boiling range is refinery gas (below 25°C). [1] It has the shortest molecules (1 to 4 carbon atoms), so it boils at the lowest temperature.

(b) A use of the gasoline fraction is as fuel for cars (petrol for vehicles). [1]

(c) As the boiling range increases, the number of carbon atoms per molecule increases. [1] Longer chains have stronger intermolecular forces, so more energy is needed to boil them, giving a higher boiling range.

(d) All the fractions come from petroleum (crude oil). [1]

(e) Petroleum is a mixture because it contains many different substances (different hydrocarbons) [1] that are not chemically combined, so they can be separated by a physical method such as fractional distillation. [1] In a compound the elements would be chemically bonded in fixed proportions and could not be separated this way.

(f) A hydrocarbon is a compound containing hydrogen and carbon only. [1] The word "only" is essential for the mark.

(g) "Finite" means the resource is being used up / will eventually run out [1] and cannot be replaced quickly (it takes millions of years to form, so it is non-renewable). [1]

Exam tip: for "mixture" answers you must say the components are not chemically combined; simply saying "it has many substances" is not enough for full marks.