Analytical techniques — AS & A Level Chemistry (9701) questions by topic
Mass spectra and infrared data drive this topic: identifying an element from isotope peak ratios, deducing molecular formulae from M, M+1 and M+2 peak heights, and reading characteristic IR absorption ranges for functional groups.
Deduce, identify, calculate, suggest and express lead the command words across 19 questions from 2023 to 2025 papers, worth 1 to 9 marks, where a wrong ratio calculation derails an otherwise sound structural deduction. Practising the M+1 syllabus formula and buffer-pH calculations with instant marking catches a mislabelled carbon count or a sign error in the Henderson-Hasselbalch equation immediately, rather than after the whole paper is submitted.
What examiners look for
- A common mistake was choosing C in the M+1 question; applying the formula 100 / (1.1 x 15) correctly gives six carbon atoms, which matches D, not C.
- Reports note candidates choosing A in the oxygen isotope question may have considered only masses 32, 34 and 36, missing that mass 33 arises from 16O-17O and mass 35 from 17O-18O.
- A recurring error in the buffer calculation was giving 5.18 instead of the correct moles at equilibrium, or 5.22 from a sign error in the Henderson-Hasselbalch equation.
- Strong answers recognised that equal heights of peaks M and M+2 indicate a bromine compound, then used the M:M+1 ratio to deduce six carbon atoms and confirm option D.
May–June 2025, Paper 11
Hydrocarbon X is saturated. Each molecule contains one ring of carbon atoms. The mass spectrum of hydrocarbon X is measured. The peak representing the M+ ion is 14 mm high. The…
Answer this question and get it marked →May–June 2025, Paper 12
A helium ion contains two protons, two neutrons and one electron. This helium ion and a proton are passed separately through a uniform electric field. The particles are travelling…
Answer this question and get it marked →The mass spectrum of CH3Cl shows a molecular ion peak, M^+, at the m/e value of 50 with a relative abundance of 18.0%. Other peaks are present in the mass spectrum. What is seen…
Answer this question and get it marked →May–June 2025, Paper 13
The mass spectrum of an organic compound has the following features: - The molecular ion peak is at m/e = 60. This peak has a relative intensity = 100. - There is a peak at m/e =…
Answer this question and get it marked →May–June 2025, Paper 14
The mass spectrum of element Z is shown. There are peaks at approximately m/e = 35 and 37 (abundance ~3:1) and at m/e = 70, 72 and 74. What is element Z? A arsenic B chlorine C…
Answer this question and get it marked →May–June 2025, Paper 42
Compound A is isopropyl propanoate, CH3CH2COOCH(CH3)2. The proton (1H) NMR spectrum of compound A shows peaks at δ 1.10, 1.50, 2.85 and 3.75 ppm (approximately). (i) State why TMS…
Answer this question and get it marked →May–June 2024, Paper 12
Compound X reacts with acidified K2Cr2O7 to form compound Y. The infrared spectrum of compound Y is shown. The spectrum shows a strong broad absorption around 2500-3000 cm^-1…
Answer this question and get it marked →May–June 2024, Paper 13
A sample of but-2-enoic acid, CH3CH=CHCOOH, is analysed using infrared spectroscopy. The infrared spectrum shows a broad peak in the range 2500-3000 cm^-1. A table of…
Answer this question and get it marked →May–June 2024, Paper 22
Compound W has molecular formula C4H10O. It contains only one functional group. Table 5.1 shows the two peaks with the greatest m/e values in the mass spectrum of W. Table 5.1 m/e…
Answer this question and get it marked →February–March 2023, Paper 12
The infrared spectrum of an organic compound is shown. The spectrum plots transmittance / % against wavenumber / cm⁻¹. It shows a moderate broad absorption around 2900–3000 cm⁻¹…
Answer this question and get it marked →February–March 2023, Paper 42
A student uses thin-layer chromatography (TLC) to analyse a mixture containing different metal cations, repeating the experiment with different solvents. Fig. 6.1 shows the…
Answer this question and get it marked →May–June 2023, Paper 11
There are two naturally occurring isotopes of bromine. One isotope has 44 neutrons. The other isotope has 46 neutrons. Ignoring fragments, how many peaks are there in the mass…
Answer this question and get it marked →May–June 2023, Paper 12
The diagram shows the relative abundance of different isotopes of lead in a sample of lead ore. The abundance of 208 is half that of 206. The abundances of 208 and 209 are equal.…
Answer this question and get it marked →May–June 2023, Paper 13
The mass spectrum of compound X has M, M+1 and M+2 peaks. Other peaks are also present. Peak M is the molecular ion peak, M+. Peak M has a relative abundance fifteen times that of…
Answer this question and get it marked →October–November 2023, Paper 11
The infrared spectrum of compound L is shown, together with a table of characteristic IR absorption ranges. The spectrum shows a broad strong absorption around 3200-3600 cm-1 and…
Answer this question and get it marked →In the mass spectrum of compound J, the ratio of the height of the M+1 ion peak to the height of the M+ ion peak is 4:91. Compound J forms a carboxylic acid when heated with…
Answer this question and get it marked →October–November 2023, Paper 12
Oxygen has three stable isotopes, 16O, 17O and 18O. All three isotopes are present in a sample of oxygen gas, O2, which was analysed using a mass spectrometer. How many peaks…
Answer this question and get it marked →October–November 2023, Paper 13
The infrared spectrum of compound L is shown. [An infrared spectrum of transmittance % against wavenumber / cm^-1 is shown. It shows a very broad, strong absorption from about…
Answer this question and get it marked →In the mass spectrum of compound J, the ratio of the height of the M+1 ion peak to the height of the M+ ion peak is 4:91. Compound J forms a carboxylic acid when heated with…
Answer this question and get it marked →Other AS & A Level Chemistry topics
- Practical skills (106)
- Hydrocarbons (65)
- Chemical bonding (63)
- The Periodic Table: chemical periodicity (59)
- Chemical energetics (53)
- Equilibria (53)
- Introduction to organic chemistry (53)
- Reaction kinetics (52)
- Carboxylic acids and derivatives (52)
- Group 2 (51)
- Carbonyl compounds (45)
- Atomic structure (44)