Unit 4 · Analysis (AS & A Level)
The Complete Cambridge International AS & A Level Chemistry (9701) Guide · Cambridge International AS & A Level Chemistry (9701)Unit 4 · Analysis (AS & A Level)
- The Complete Cambridge International AS & A Level Chemistry (9701) Guide
- Cambridge International AS & A Level Chemistry (9701)
- 4 sections
Cambridge International does not publish a per-unit weighting for this exam. Exam structure (official): AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 23%); A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 11.5%). Be ready to carry the same unit skills and representations into a complete answer on every paper. Analysis begins by naming the signal: a peak, spot, absorbance, titre, or observation. Its scale and uncertainty determine which conclusion the evidence can support.
- How Cambridge International AS & A Level Chemistry (9701) assesses this Cambridge International publishes no per-unit percentage for Cambridge International A Level Chemistry; Paper 1 accounts for 31% of the AS Level total and 15.5% of the A Level total. · AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 23%) | A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 11.5%) · show the model with a labeled mass or infrared spectrum, a calibration graph with equation, units, and supported range, a measurement table that retains repeats, spread, and anomalies, a combined spectral-assignment table, a calibration line with gradient, intercept, range, and units, a planned results table with repeats, uncertainty, and an evaluation criterion
- Key skills Infrared Spectroscopy: Identifying Functional Groups, Mass Spectrometry: Isotopic Abundance, Relative Atomic Mass and Molecular Ion, [M+1] and [M+2] Peaks, Mass Spectrometry: Fragmentation and Identifying Molecules, Thin-Layer Chromatography and Gas/Liquid Chromatography (A Level), Carbon-13 NMR Spectroscopy (A Level), Proton NMR Spectroscopy (A Level)
- How to study for Unit 4 This page turns a labeled mass or infrared spectrum, a calibration graph with equation, units, and supported range, a measurement table that retains repeats, spread, and anomalies, a combined spectral-assignment table, a calibration line with gradient, intercept, range, and units, a planned results table with repeats, uncertainty, and an evaluation criterion into one route: Name the measured signal, its unit, range, and uncertainty before proposing a structure or concentration..
- The organizing decision Combine independent analytical signals only after each measurement has been translated into a bounded chemical constraint.
- What A Level adds Use combined spectra, calibration, controls, repeats, and uncertainty to reach a conclusion no more precise than the evidence. Topics: Thin-Layer Chromatography and Gas/Liquid Chromatography; Carbon-13 NMR Spectroscopy; Proton NMR Spectroscopy.
What Cambridge International AS & A Level Chemistry (9701) Unit 4 covers
Use this map to connect each assessed skill to the relationship or representation that makes it visible.
Infrared Spectroscopy: Identifying Functional Groups
molecular ion; calibration curve; measurement uncertainty02Mass Spectrometry: Isotopic Abundance, Relative Atomic Mass and Molecular Ion, [M+1] and [M+2] Peaks
molecular ion; calibration curve; measurement uncertainty03Mass Spectrometry: Fragmentation and Identifying Molecules
molecular ion; calibration curve; measurement uncertainty04Thin-Layer Chromatography and Gas/Liquid Chromatography (A Level)
proton NMR; non-zero intercept; percentage uncertainty05Carbon-13 NMR Spectroscopy (A Level)
proton NMR; non-zero intercept; percentage uncertainty06Proton NMR Spectroscopy (A Level)
proton NMR; non-zero intercept; percentage uncertaintyCambridge International does not publish a per-unit weighting for this exam.
Official unit name and weighting: Cambridge International syllabus.
Analysis
Connect the published share to the unit model
Analysis begins by naming the signal: a peak, spot, absorbance, titre, or observation. Its scale and uncertainty determine which conclusion the evidence can support.
No separate percentage is published for this domain. Five pages develop spectra, calibration, chromatography, and recording practice without implying an official priority order.
Use the 3×3 map to move from raw signal to chemical claim. Preserve units, calibration range, and relevant resolution at every step. Independent techniques strengthen a conclusion only when each observation is stated before the combined structural inference.
Treat every analytical result as a chain from measurement to constraint to conclusion. Begin with hard information such as formula, unsaturation, calibration range, or instrument resolution. Assign only diagnostic signals, then reconcile all environments, peak areas, splitting, masses, absorptions, or retention measurements with one structure or concentration. A proposed answer must account for every supplied datum; if two possibilities remain, state the unresolved ambiguity instead of forcing certainty. For graphical data, identify variables and units, use a scale that displays the observations clearly, retain spread and anomalies, and extract gradient, intercept, or trend from suitable points. End with a result whose precision and confidence do not exceed the evidence.
In a measurement table, separate each raw reading from the processed value and the final chemical claim. Record the instrument display with its unit and resolution, show the conversion applied, and only then state the result supported by the record. For titration data, preserve every trial, identify the concordant values, and explain any exclusion rather than erasing it. Keep the selected mean, conversion factors, amount ratio, final unit, and uncertainty visible through the calculation. This recording audit lets another student reproduce the numerical decision and exposes any unsupported precision.
The decision that organizes this unit
Define the system and choose the route before calculating
Combine independent analytical signals only after each measurement has been translated into a bounded chemical constraint.
Name the measured signal, its unit, range, and uncertainty before proposing a structure or concentration.
Mechanism route and repair branches
Relationships to preserve
- Mass spectra is shown through assign m/z and ion role.
- Infrared is shown through bond and region stated.
- Experimental data is shown through unit, spread, anomaly, conclusion.
- Combined spectra is shown through assign every signal.
- Calibration is shown through equation, unit, interpolation.
- Planning is shown through variables, repeats, safety, criterion.
Representations to read
- a labeled mass or infrared spectrum
- a calibration graph with equation, units, and supported range
- a measurement table that retains repeats, spread, and anomalies
- a combined spectral-assignment table
- a calibration line with gradient, intercept, range, and units
- a planned results table with repeats, uncertainty, and an evaluation criterion
Branches to reject
- using one peak as a complete structural identity
- extrapolating beyond the supported calibration range
- reporting more precision or certainty than the instrument and data support
- forcing one structure before assigning every supplied signal
- ignoring a non-zero calibration intercept
- proposing an improvement without linking it to random variation or consistent bias
| Key concept | Why it's hard | What scores |
|---|---|---|
| Mass spectra | Position and abundance differ | Assign m/z and ion role |
| Infrared | Absence can constrain | Bond and region stated |
| Experimental data | Precision differs from accuracy | Unit, spread, anomaly, conclusion |
How Cambridge International AS & A Level Chemistry (9701) assesses Analysis (AS & A Level)
What a complete response must make visible
Match the task to evidence that a reader can audit, then check the most likely reasoning failure before finalizing the response.
| Task | Evidence to show | Hurdle |
|---|---|---|
| Infrared Spectroscopy: Identifying Functional Groups | molecular ion; calibration curve; measurement uncertainty | using one peak as a complete structural identity |
| Mass Spectrometry: Isotopic Abundance, Relative Atomic Mass and Molecular Ion, [M+1] and [M+2] Peaks | molecular ion; calibration curve; measurement uncertainty | extrapolating beyond the supported calibration range |
| Mass Spectrometry: Fragmentation and Identifying Molecules | molecular ion; calibration curve; measurement uncertainty | reporting more precision or certainty than the instrument and data support |
| Thin-Layer Chromatography and Gas/Liquid Chromatography (A Level) | proton NMR; non-zero intercept; percentage uncertainty | forcing one structure before assigning every supplied signal |
| Carbon-13 NMR Spectroscopy (A Level) | proton NMR; non-zero intercept; percentage uncertainty | ignoring a non-zero calibration intercept |
| Proton NMR Spectroscopy (A Level) | proton NMR; non-zero intercept; percentage uncertainty | proposing an improvement without linking it to random variation or consistent bias |
Combine mass and infrared evidence
Read each question as it appears on the exam paper, choose your answer, then tap it to see the feedback.
Practice 1: Combine mass and infrared evidence
Compound X has the molecular formula C₃H₆O.
The mass spectrum of X has a molecular ion peak at m/z 58 and a strong fragment peak at m/z 43. Its infrared spectrum has an absorption near 1715 cm⁻¹ and no broad O–H absorption. Deduce the structure of X and explain how the evidence supports your answer.
[4]Show all necessary working.
Account for every item of spectral evidence.
A. Identify propanone from the C=O absorption alone.
❌ Not quite 😭 The absorption supports a carbonyl group, but one peak does not establish the complete structure. This leaves the formula, molecular ion, missing O–H absorption and fragment unaccounted for.
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B. Calculate one degree of unsaturation, assign C=O and the missing O–H, then check propanone against m/z 58 and 43.
✅ Correct! 😊 This builds independent constraints before naming the molecule. Propanone fits the formula and molecular ion, while CH₃CO⁺ explains the strong fragment at m/z 43.
C. Choose propan-1-ol because the formula contains one oxygen atom.
❌ Not quite 😭 An oxygen atom does not automatically mean an alcohol. Propan-1-ol has a different molecular formula, and the absent broad O–H absorption conflicts with that choice.
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D. Assign m/z 43 as the molecular ion and propose an aldehyde without checking the other data.
❌ Not quite 😭 The molecular ion is stated to be m/z 58, so m/z 43 must be treated as a fragment. An unsupported aldehyde also fails to reconcile every supplied signal.
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Full explanation
- Step 1C₃H₆O has one degree of unsaturation, so a double bond or ring must be present.
- Step 2The absorption near 1715 cm⁻¹ supports C=O; the missing broad O–H absorption argues against an alcohol.
- Step 3Propanone, CH₃COCH₃, has the correct formula and relative molecular mass of 58.
- Step 4Cleavage produces CH₃CO⁺ at m/z 43, so the proposed structure accounts for every observation.
Practice 2: Use a calibration equation within its range
A calibration line for solutions from 0.50 to 4.00 mmol dm⁻³ has the equation A = 0.160c + 0.020, where A is absorbance and c is concentration in mmol dm⁻³.
An unknown solution gives A = 0.420. Calculate its concentration and explain whether the calibration is being used by interpolation or extrapolation.
[4]Show all necessary working.
Give your answer in mmol dm⁻³.
A. c = 0.420 ÷ 0.160 = 2.63 mmol dm⁻³; interpolation
❌ Not quite 😭 This divides by the gradient but ignores the non-zero intercept. Although 2.63 lies within the stated range, the concentration is not calculated from the complete equation.
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B. c = (0.420 − 0.020) ÷ 0.160 = 2.50 mmol dm⁻³; interpolation
✅ Correct! 😊 This rearranges the full calibration equation and retains the intercept. The result lies between 0.50 and 4.00 mmol dm⁻³, so it is an interpolation.
C. c = (0.420 + 0.020) ÷ 0.160 = 2.75 mmol dm⁻³; extrapolation
❌ Not quite 😭 Adding the intercept reverses the required rearrangement. The claimed extrapolation is also wrong because the calculated value remains inside the supported concentration range.
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D. c = 0.160 × 0.420 + 0.020 = 0.087 mmol dm⁻³; interpolation
❌ Not quite 😭 The equation predicts absorbance from concentration, so multiplying absorbance by the gradient does not invert it. The resulting value is outside the stated range and cannot be called interpolation.
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Full explanation
- Step 1Keep the response and concentration distinct: A is measured, while c is required.
- Step 2Rearrange the complete line, including its intercept: c = (A − 0.020) ÷ 0.160.
- Step 3Substitution gives c = (0.420 − 0.020) ÷ 0.160 = 2.50 mmol dm⁻³.
- Step 4Because 2.50 mmol dm⁻³ lies within 0.50–4.00 mmol dm⁻³, the use is interpolation.
Key terms for Unit 4: Analysis (AS & A Level)
Models, uses, and boundaries
- Data Map
- Mean and range preserve center and spread. Use this data map when the question calls for the relationship described here.
- Spectral Constraint
- Formula and mass bound the candidates. Use this spectral constraint when the question calls for the relationship described here.
- Calibration
- Division by slope produces concentration. Use this calibration when the question calls for the relationship described here.
- Alvc-U4-A01
- The diagram labels lid, front, spot, origin, solvent, and measurement direction. Use this alvc-u4-a01 when the question calls for the relationship described here.
- Repeats
- The mean displays contributing measurements. Use this repeats when the question calls for the relationship described here.
- Analysis Map
- A defensible structure lies at intersecting evidence. Use this analysis map when the question calls for the relationship described here.
- Structure
- Formula and environments converge on propanoic acid. Use this structure when the question calls for the relationship described here.
- Linear Fit
- Rearrangement retains the measured intercept. Use this linear fit when the question calls for the relationship described here.
- Alvc-U8-A01
- The setup labels vessel, heater, probe, delivery path, syringe, and timer. Use this alvc-u8-a01 when the question calls for the relationship described here.
- Uncertainty
- The ratio shows why small readings carry larger percentages. Use this uncertainty when the question calls for the relationship described here.
Cambridge International AS & A Level Chemistry (9701) Unit 4 FAQ
How much of Cambridge International AS & A Level Chemistry (9701) does Unit 4 carry?
Cambridge International does not publish a per-unit weighting for this exam.
What is the first move on a Analysis (AS & A Level) problem?
Name the measured signal, its unit, range, and uncertainty before proposing a structure or concentration.
Which relationships should I preserve?
Mass spectra is shown through assign m/z and ion role. Infrared is shown through bond and region stated. Experimental data is shown through unit, spread, anomaly, conclusion. Combined spectra is shown through assign every signal. Calibration is shown through equation, unit, interpolation. Planning is shown through variables, repeats, safety, criterion.
Which representations should I practice?
Practice moving among a labeled mass or infrared spectrum, a calibration graph with equation, units, and supported range, a measurement table that retains repeats, spread, and anomalies, a combined spectral-assignment table, a calibration line with gradient, intercept, range, and units, a planned results table with repeats, uncertainty, and an evaluation criterion.
What error should I check before submitting an answer?
Check for using one peak as a complete structural identity; extrapolating beyond the supported calibration range; reporting more precision or certainty than the instrument and data support; forcing one structure before assigning every supplied signal; ignoring a non-zero calibration intercept; proposing an improvement without linking it to random variation or consistent bias.
Evidence workshop
Continue from the free model into complete practice
The full unit guide continues with the chapter’s worked examples, figures, scoring tables, and answer checks.
- Combine mass and infrared evidence
- Interpolate a calibration with uncertainty
- Measure a retention factor from one origin
- Match precision to the instrument
Full unit practice. Open the complete guide for the full evidence workshop and synthesis.
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Cambridge International does not publish a per-unit weighting for this exam.How to study Cambridge International AS & A Level Chemistry (9701) Unit 4
Start with the organizing decision
Before solving, restate the decision in operational terms: Combine independent analytical signals only after each measurement has been translated into a bounded chemical constraint.. Your first written move should be to Name the measured signal, its unit, range, and uncertainty before proposing a structure or concentration..
Practice the same idea in several representations
Rotate through a labeled mass or infrared spectrum, a calibration graph with equation, units, and supported range, a measurement table that retains repeats, spread, and anomalies, a combined spectral-assignment table, a calibration line with gradient, intercept, range, and units, a planned results table with repeats, uncertainty, and an evaluation criterion. Use each representation to practice Infrared Spectroscopy: Identifying Functional Groups, Mass Spectrometry: Isotopic Abundance, Relative Atomic Mass and Molecular Ion, [M+1] and [M+2] Peaks, Mass Spectrometry: Fragmentation and Identifying Molecules, Thin-Layer Chromatography and Gas/Liquid Chromatography (A Level), Carbon-13 NMR Spectroscopy (A Level), Proton NMR Spectroscopy (A Level), and explain what stays invariant when the surface form changes.
Turn each error into a repair check
After every attempt, audit the response for using one peak as a complete structural identity; extrapolating beyond the supported calibration range; reporting more precision or certainty than the instrument and data support; forcing one structure before assigning every supplied signal; ignoring a non-zero calibration intercept; proposing an improvement without linking it to random variation or consistent bias. Then redo only the first step that made the reasoning diverge, keeping units, direction, and model conditions visible.
Confirm current course details in the official Cambridge International syllabus for the 2025-2027 administration.
Where to go next
Return to the Cambridge International AS & A Level Chemistry (9701) to see every unit and plan your revision.