DP Chemistry (first assessment 2025)
Question 19M.1A.SL.TZ2.32
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.1A.SL.TZ2.32 |
| Level | SL | Paper | 1A | Time zone | TZ2 |
| Command term | Question number | 32 | Adapted from | N/A |
32.
[Maximum mark: 1]
19M.1A.SL.TZ2.32
Which compound has the lowest boiling point?
A. CH3CH2CH2CH2CH2CH3
B. CH3CH2CH2CH2CH3
C. CH3CH(CH3)CH2CH3
D. CH3C(CH3)2CH3
[1]
Markscheme
D
Examiners report
Surprisingly, this was one of the challenging questions on the paper. Only 63 % of the candidates chose dimethylpropane as the compound having the lowest boiling point. The most commonly chosen distractor was pentane (B) which did not take into account the effect of branching on the strength of London dispersion forces.
Syllabus sections
Structure 2. Models of bonding and structure » Structure 2.2—The covalent model » Structure 2.2.9—Given comparable molar mass, the relative strengths of intermolecular forces are generally: London (dispersion) forces < dipole–dipole forces < hydrogen bonding. Explain the physical properties of covalent substances to include volatility, electrical conductivity and solubility in terms of their structure.