Home / iGCSE Chemistry (0620) Theory (Core):12.4 Separation and purification: Exam Style Questions Paper 3
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 12.4 — Separation and purification — simple distillation (Part (a))
• Topic 11.3 — Fuels — fractional distillation of petroleum (Parts (b)(i) to (b)(iv))
(a)
Water evaporates / boils from the aqueous copper(II) sulfate solution when heated, but the copper(II) sulfate does not evaporate because it has a much higher boiling point. The water vapour then passes into the condenser, where it cools and condenses back into liquid water, which is collected — leaving the copper(II) sulfate behind in the flask.
(b)(i)
The X should be drawn in the lowest section of the fractionating column (where bitumen collects). Hydrocarbons with the highest viscosity are the longest-chain molecules, which are the heaviest and least volatile — they condense at the bottom of the column where temperatures are highest.
(b)(ii)
The fraction labelled A is kerosene / paraffin. In a typical fractionating column, kerosene is collected in the middle region and is used as jet fuel, making it a key fraction by position relative to the labelling shown.
(b)(iii)
The fraction with the lowest boiling point is refinery gas. It consists of the shortest hydrocarbon chains (mainly C₁–C₄), which have the weakest intermolecular forces, meaning they require the least energy to vaporise and therefore have the lowest boiling points — they exit at the top of the column.
(b)(iv)
Bitumen is used for making / surfacing roads (tarmac). It is the heaviest fraction from petroleum distillation, with very long hydrocarbon chains, giving it a thick, sticky consistency that makes it ideal as a road-surfacing material.