Modern Analytical Techniques II | Edexcel A-Level Chemistry (9CH0)
Modern Analytical Techniques II
- 51 questions
- 4 subtopics
- Paper 2: advanced organic and physical chemistry
- Paper 2 and Paper 3
Covers carbon-13 and proton NMR and what each feature of a spectrum reveals, and the chromatographic methods that separate a mixture before analysis..
It covers carbon-13 and proton NMR, splitting, integration and the reference standard, chromatography and high-resolution mass spectrometry.
Sample questions from Modern Analytical Techniques II
Answer each one closed book first, then open the answer.
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Carbon-13 and proton NMR
How can you determine the number of distinct carbon environments in a molecule from its carbon-13 NMR spectrum?
Show the answer
The number of peaks in the spectrum equals the number of distinct carbon environments in the molecule. -
Carbon-13 and proton NMR
Why do protons attached to different functional groups appear at different chemical shift values in proton NMR?
Show the answer
Because different chemical shift values correspond to protons in different chemical environments. -
Splitting, integration and the reference standard
How many equivalent neighbouring protons on adjacent carbons produce a triplet in proton NMR?
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Two equivalent neighbouring protons on adjacent carbons. -
Splitting, integration and the reference standard
Why is TMS chosen as the NMR reference standard?
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All twelve of its hydrogen atoms are in the same environment, so it gives a single sharp peak. It is inert, volatile enough to be removed afterwards, and absorbs well clear of the signals of most organic compounds. -
Chromatography
What does the numerator in the Rꜰ formula represent?
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The distance travelled by the substance from the origin. -
Chromatography
Define retention time in the context of chromatography.
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Retention time is the time taken for a component to pass through the chromatography column. -
High-resolution mass spectrometry
Calculate the accurate Mᵣ of ethene, C₂H₄ (¹H = 1.0078, ¹²C = 12.0000).
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Mᵣ = 2(12.0000) + 4(1.0078) = 28.0312. -
High-resolution mass spectrometry
A compound has a molecular ion at m/z 44.0261. Is its formula CO₂, C₃H₈ or C₂H₄O, and what could it be (¹H = 1.0078, ¹²C = 12.0000, ¹⁶O = 15.9949)?
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C₂H₄O, whose accurate Mᵣ is 44.0261 (CO₂ is 43.9898 and C₃H₈ is 44.0624). A possible structure is ethanal, CH₃CHO.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Carbon-13 and proton NMR | Recall questions on what NMR detects, on how many signals a molecule gives, and on the chemical shifts of the common carbon and proton environments. | 10 |
| Splitting, integration and the reference standard | Recall questions on the n plus one rule, on reading an integration trace, on the deuterium exchange for OH and NH, and on why TMS is used as the standard. | 14 |
| Chromatography | Mobile and stationary phases and how they separate a mixture, calculating Rf values, HPLC and gas chromatography as column methods, retention time, and coupling GC or HPLC to mass spectrometry for uses such as forensic work and drug testing. | 14 |
| High-resolution mass spectrometry | Accurate relative molecular masses to four decimal places, why carbon-12 is exactly 12.0000, calculating accurate masses from isotopic masses, telling apart formulae with the same whole-number Mr such as CO, N2 and C2H4, and why an accurate mass alone cannot identify a structure. | 13 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
Edexcel A-Level Chemistry Active Recall Guide
Every topic, not just this one. 1,534 questions with their answers.