Edexcel A Level Chemistry
Edexcel A Level Chemistry Topic 19: Modern Analytical Techniques II Exam Questions
Free Edexcel A Level Chemistry exam questions for Topic 19: Modern Analytical Techniques II, with a mark scheme for every pack. Covers carbon-13 and proton NMR spectroscopy, chemical shift, splitting patterns, TMS, and chromatography including TLC, HPLC and GC.
Topic 19: Modern Analytical Techniques II exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel A Level Chemistry Topic 19: Modern Analytical Techniques II
Topic 19 of Edexcel A Level Chemistry, Modern Analytical Techniques II, extends the mass spectrometry and infrared work of Topic 7. You interpret carbon-13 NMR spectra to count carbon environments and use chemical shift values from the data booklet, then interpret high resolution proton NMR spectra using chemical shift, relative peak area and splitting patterns from the n+1 rule. TMS as the reference and deuterated solvents are explained. The topic also covers chromatography: thin-layer chromatography with Rf values, high performance liquid chromatography and gas chromatography with retention times, including their combination with mass spectrometry. It is assessed in Paper 2. Examiners often combine all techniques to deduce a structure.
What you need to know
- Carbon-13 NMR The number of peaks shows the number of different carbon environments. Chemical shift values from the data booklet indicate the type, such as C=O between about 160 and 220 ppm.
- Proton NMR The number of peaks shows proton environments, chemical shift shows their type, and the relative peak area (integration) shows the ratio of protons in each environment.
- Splitting A peak is split into n+1 lines by n hydrogens on adjacent carbon atoms: doublet, triplet, quartet. OH protons usually appear as singlets.
- TMS and solvents Tetramethylsilane is the reference at 0 ppm because it gives a single strong peak away from other signals and is inert. Deuterated solvents such as CDCl3 are used so the solvent gives no proton signal.
- Thin-layer chromatography Separates by relative affinity for the stationary phase and solubility in the mobile phase. Rf = distance moved by spot/distance moved by solvent front.
- HPLC and GC HPLC uses a liquid mobile phase forced at high pressure through a packed column. GC uses an inert gas mobile phase. Components are identified by retention time, and coupling to mass spectrometry identifies each component.
Common mistakes in Topic 19: Modern Analytical Techniques II
- Counting the protons on the same carbon when applying the n+1 rule; only neighbouring carbons count.
- Reading peak heights instead of peak areas to find proton ratios.
- Assuming the number of 13C peaks equals the number of carbons; equivalent carbons give a single peak.
- Measuring Rf from the bottom of the plate instead of the baseline.
- Forgetting that symmetrical molecules have fewer environments than expected.
Try three Topic 19: Modern Analytical Techniques II exam-style questions
1. A spot on a TLC plate moved 2.4 cm and the solvent front moved 6.0 cm from the baseline. Calculate the Rf value. (1 mark)
Show the mark scheme answer
Rf = 2.4/6.0 = 0.40.
2. Predict the number of peaks and the splitting patterns in the proton NMR spectrum of propanone and of chloroethane. (3 marks)
Show the mark scheme answer
Propanone: one peak; singlet (no adjacent H on a different environment); chloroethane: two peaks, CH3 triplet and CH2 quartet (ratio 3:2).
3. How many peaks would be seen in the carbon-13 NMR spectrum of propan-2-ol? Explain. (2 marks)
Show the mark scheme answer
Two peaks; the two CH3 carbons are equivalent and the CH(OH) carbon is a different environment.
Topic 19: Modern Analytical Techniques II FAQs
What does Edexcel A Level Chemistry Topic 19 cover?
It covers carbon-13 and proton NMR spectroscopy, including chemical shift and splitting, and chromatography by TLC, HPLC and GC.
Which paper is Modern Analytical Techniques II examined in?
Topic 19 is assessed in Paper 2, Advanced Organic and Physical Chemistry, and structure-deduction questions also appear in Paper 3.
How do I solve combined spectra problems?
Use mass spectrometry for Mr, IR for functional groups, 13C NMR for carbon environments and proton NMR for environments, ratios and neighbours, then check the structure fits all data.
