DP Chemistry (first assessment 2025)
Question 22M.2.SL.TZ2.8b
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.SL.TZ2.8b |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | State | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
22M.2.SL.TZ2.8b
(b)
State two features showing that propane and butane are members of the same homologous series.
[2]
Markscheme
same general formula / CnH2n+2 ✔
differ by CH2/common structural unit ✔
Accept "similar chemical properties".
Accept “gradation/gradual change in physical properties”.
Examiners report
This easy question was quite well answered; same/similar physical properties and empirical formula were common errors.
Candidates misinterpreted the question and mentioned CH3+, i.e., the lost fragment; the other very common error was -COOH which shows a complete lack of understanding of MS considering the question is about butane so O should never appear.
Syllabus sections
Structure 3. Classification of matter » Structure 3.2—Functional groups: Classification of organic compounds » Structure 3.2.3—A homologous series is a family of compounds in which successive members differ by a common structural unit, typically CH2. Each homologous series can be described by a general formula. Identify the following homologous series: alkanes, alkenes, alkynes, halogenoalkanes, alcohols, aldehydes, ketones, carboxylic acids, ethers, amines, amides and esters.