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.