An experimental refinery uses a heater connected to a fractionating column. Only vapours from the heater pass into the bottom of the column. Any liquid remains in the heater.
During normal operation, the crude oil is heated to 280 °C.
| Hydrocarbon group | Boiling point range in °C | Section of the column where the group is collected |
|---|---|---|
| P | 220–260 | lower |
| Q | 120–160 | middle |
| R | 40–80 | upper |
A sample of the crude oil and samples from the collected fractions are analysed. The results show:
| Sample | Hydrocarbon groups identified |
|---|---|
| Crude oil before separation | P, Q and R |
| Lower fraction after separation | P only |
| Middle fraction after separation | Q only |
| Upper fraction after separation | R only |
Explain why all three groups enter the column as vapours at 280 °C and explain the pattern in the table showing where they are collected.
A fault limits the temperature in the heater to 180 °C. Explain which groups would enter the column as vapours and predict where the remaining group would be found.
Use the results to justify whether the separation caused a chemical change.
91 exam-style questions on AQA GCSE Chemistry 7.1 Carbon compounds as fuels and feedstock, covering 7.1.1 Crude oil, hydrocarbons and alkanes, 7.1.2 Fractional distillation and petrochemicals, 7.1.3 Properties of hydrocarbons, and 7.1.4 Cracking and alkenes. Each one has a worked solution and a mark scheme showing where the marks go.