Community Q&A
A-Level Chemistry May/June 2025 Q7(b)(ii): A 0.10 moldm-3 solution of diethylamine, (CH3CH2)2NH, has a higher pH than a 0.10 moldm…
A-Level Chemistry · Paper 9701/42 · May/June 2025 · Question 7(b)(ii) · [2 marks]
A 0.10 moldm-3 solution of diethylamine, (CH3CH2)2NH, has a higher pH than a 0.10 moldm-3 solution of 2-aminobutane, CH3CH(NH2)CH2CH3. Suggest why.
A full-marks model answer with a mark-by-mark examiner breakdown is below.
1 answer
- accepted ✓
Diethylamine is a secondary amine, with two electron-donating ethyl groups attached directly to the nitrogen atom. 2-aminobutane is a primary amine, with only one alkyl group attached to the nitrogen atom.
The two ethyl groups in diethylamine exert a greater combined positive inductive effect than the single alkyl group in 2-aminobutane. This increases the electron density on the nitrogen atom in diethylamine more effectively, making its lone pair of electrons more available to accept a proton (H⁺). Therefore, diethylamine is a stronger base and its solution has a higher pH.
How the marks are awarded
- M1 — Correctly identifying that diethylamine has two electron-donating alkyl (ethyl) groups attached to the nitrogen atom, in contrast to 2-aminobutane which has only one.
- M2 — Explaining that the greater electron-donating effect increases the electron density on the nitrogen atom, which makes the lone pair more available to accept a proton.
Common mistakes
- Simply stating that diethylamine has 'more alkyl groups' without specifying they are attached to the nitrogen atom.
- Failing to explicitly link the electron-donating effect to the increased availability of the lone pair on the nitrogen atom.
- Incorrectly identifying 2-aminobutane as a secondary amine because the -NH2 group is on a secondary carbon atom.
- Discussing steric hindrance, which is not the primary factor determining Brønsted-Lowry basicity in this context.
Examiner tip: When comparing the basicity of amines, always link the number of electron-donating alkyl groups attached to the nitrogen atom to the resulting electron density and availability of its lone pair.
AI-generated model answer, grounded in the official Cambridge mark scheme and reviewed by the MarkScheme team. Mark your own answer to this question →
Your answer
Sign in to answer this question.