| Date | May 2018 | Marks available | 1 | Reference code | 18M.3.hl.TZ1.20 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate | Question number | 20 | Adapted from | N/A |
Question
Organic solvents are commonly used in the pharmaceutical industry.
Hexane and propanone have vapour pressures of 17 kPa and 24 kPa respectively at 20 °C.
Calculate the vapour pressure, in kPa, at 20 °C of a mixture containing 60% hexane and 40% propanone by mole fraction, using Raoult’s law and assuming the mixture is ideal.
[1]
a.
Explain how hexane and propanone may be separated by fractional distillation.
[3]
b.
Markscheme
«vapour pressure = 0.6 × 17 + 0.4 × 24 =»
19.8 «kPa»
[1 mark]
a.
Any three of:
different molar masses
OR
different strength of intermolecular forces
different boiling points
temperature in «fractionating» column decreases upwards
«components» condense at different temperatures/heights
OR
«component with» lower boiling point leaves column first
[3 marks]
b.
Examiners report
[N/A]
a.
[N/A]
b.
