June 2026
The 2025 VCE Chemistry exam showed that analytical chemistry is not about recognising instruments or memorising tests.
It is about using evidence.
Students were asked to interpret melting point data, identify functional groups using chemical tests, choose separation techniques, read spectra, work with isotope patterns, calculate titration results and evaluate whether data supported a hypothesis.
These questions rewarded students who could ask the right chemical question:
What does this result show?
Which compound would give this observation?
Which technique suits this mixture?
Which peak identifies the molecular ion?
What does the isotope pattern imply?
How does the titre relate to the aliquot?
Does the calculated result support the hypothesis?
In VCE Chemistry, analytical data only earns marks when students can interpret it chemically.
Melting point was evidence of purity
Question 28 asked about a blended vanillin sample.
Pure vanillin has a melting point of 82–83 °C. The question stated that vanillin is often blended with significant amounts of cheaper compounds that have similar melting points.
The correct melting point range for the blend was broader and lower than the pure substance.
This is a classic purity principle. Impurities disrupt the regular packing of particles in the solid. As a result, the sample melts over a wider temperature range and usually at a lower temperature than the pure compound.
The phrase “significant amounts” mattered. A very narrow melting point range close to the pure value would not be expected if the blend contained substantial impurity.
This question rewarded students who understood what melting point data indicates.
A sharp, narrow melting point suggests purity.
A broad, depressed melting point suggests impurity.
Functional group tests had to distinguish the substances
Question 27 asked which laboratory test could confirm that a sample was pure geranial and not pure linalool.
Geranial is an aldehyde. Linalool is a tertiary alcohol.
The correct test was acidified dichromate. Geranial is readily oxidised and causes the dichromate solution to change from orange to green. Linalool, as a tertiary alcohol, is not readily oxidised, so the solution remains orange.
This question carried an important analytical lesson.
A test is only useful if it gives different results for the two substances being compared.
Bromine solution would not distinguish geranial from linalool because both compounds contain carbon-carbon double bonds and can decolourise bromine. Sodium hydrogen carbonate would not work because neither compound contains a carboxyl group. Acidified permanganate was not correct as written because the colour change direction was wrong.
The question was not asking which test can react with an organic compound.
It was asking which test identifies the difference.
Separation methods followed physical properties
Question 25 asked which method would be most suitable to separate volatile polar compounds with similar boiling points from ethanol.
The correct answer was fractional distillation.
This method is suitable because the compounds are volatile and have similar boiling points. Fractional distillation provides repeated vaporisation-condensation cycles, allowing better separation of liquids whose boiling points are close.
Simple distillation is more suitable when boiling points are significantly different. Solvent extraction is useful when substances have distinctly different solubilities or polarities, but it would not effectively separate polar compounds from one another in this context.
This question rewarded students who could match technique to property.
The method is not chosen because it sounds familiar. It is chosen because it suits the mixture.
Spectroscopy required structural evidence
Question 30 asked students to identify the ¹³C NMR spectrum of pentan-3-one.
Pentan-3-one is symmetrical. It has five carbon atoms, but only three distinct carbon environments. Therefore, its ¹³C NMR spectrum should show three signals.
It is also a ketone, so one signal should appear in the carbonyl region around 205–220 ppm.
This question tested one of the central ideas in NMR.
The number of signals corresponds to the number of distinct chemical environments, not the total number of atoms.
Equivalent carbons produce the same signal.
Students who simply count carbon atoms will overpredict the number of peaks. Students who recognise symmetry can interpret the spectrum correctly.
Molecular formulas required structural reading
Question 26 gave skeletal structures for geranial and linalool and asked students to identify their molecular formulas.
The correct formulas were:
Geranial: C₁₀H₁₆O
Linalool: C₁₀H₁₈O
This was an analytical skill question because students needed to read skeletal structures accurately. In skeletal formulas, carbon atoms appear at line ends and vertices. Hydrogen atoms bonded to carbon are usually not drawn and must be inferred from valency. Heteroatoms such as oxygen are shown explicitly.
A small error in structural interpretation changes the formula.
This matters because formula determination is often the starting point for spectroscopic analysis, reaction prediction and compound identification.
IR spectra required bond-level interpretation
Section B Question 4 included an IR spectrum from a separated sample and asked students to determine whether the sample was an amine or a carboxylic acid.
This required students to interpret absorption bands as evidence of particular bonds and functional groups.
A carboxylic acid would be expected to show a broad O–H absorption and a strong C=O absorption. An amine would show N–H absorptions but would not show the same carboxylic acid carbonyl pattern.
The important point is that IR evidence is functional group evidence.
A student should not simply guess the compound from the surrounding context. They should identify the absorption features that support the conclusion.
The spectrum is the evidence.
Mass spectra required isotope reasoning
The 2025 exam also included an organic compound containing oxygen and chlorine. Students were given mass spectral information and isotope details: oxygen has only the stable isotope ¹⁶O, while chlorine has stable isotopes ³⁵Cl and ³⁷Cl.
This kind of question requires students to interpret isotope patterns.
Chlorine-containing compounds often show molecular ion peaks two mass units apart because ³⁵Cl and ³⁷Cl differ by two atomic mass units. The relative intensities can support the presence of chlorine.
Students also needed to understand that isomers of the same compound have the same molecular formula and therefore the same molecular ion peak. Different structures can have the same molecular mass.
This is where analytical chemistry becomes reasoning, not recognition.
A mass spectrum is not a picture to memorise. It is evidence about molecular mass, fragments and isotopes.
The base peak was not necessarily the molecular ion
Mass spectrum questions often test the difference between the base peak and the molecular ion peak.
The base peak is the most intense peak in the spectrum. It is assigned a relative intensity of 100%. It is not necessarily the molecular ion peak.
The molecular ion peak corresponds to the intact molecule after losing one electron. It helps determine molecular mass. The base peak usually represents the most stable or abundant fragment ion.
Students often confuse these.
The 2025 exam rewarded students who could identify peaks according to their meaning, not merely their size or position.
Analytical chemistry depends on knowing what each signal represents.
Titration data required aliquot reasoning
Question 6 involved oxalate ions in spinach and a titration with acidified potassium permanganate.
The report noted that students commonly failed to allow for dilution or reaction stoichiometry.
This is one of the most common analytical chemistry errors.
Karolina prepared a solution in a 500 mL volumetric flask, then titrated a 25.0 mL aliquot. The titre result gave information about the aliquot, not the whole 500 mL solution. Students needed to scale from the aliquot to the full solution.
The report gave the average titre as 15.42 mL. From this:
n(MnO₄⁻) = 0.0020 × 15.42 ÷ 1000 = 3.084 × 10⁻⁵ mol
Using the reaction stoichiometry:
n(C₂O₄²⁻) in 25 mL = 5/2 × 3.084 × 10⁻⁵ = 7.71 × 10⁻⁵ mol
Scaling to 500 mL:
n(C₂O₄²⁻) in 500 mL = 500 ÷ 25 × 7.71 × 10⁻⁵ = 1.542 × 10⁻³ mol
Then:
m(C₂O₄²⁻) = 88.0 × 1.542 × 10⁻³ = 0.136 g
This calculation was not difficult because of arithmetic. It was difficult because of analytical reasoning.
The aliquot had to be connected to the original sample.
Stoichiometry was part of the evidence
In the oxalate titration, the permanganate titre did not directly equal the amount of oxalate.
Students needed the balanced redox relationship. The report used a 5:2 ratio between oxalate ions and permanganate ions.
That mole ratio was essential.
If students calculated moles of permanganate and treated that as moles of oxalate, the result was wrong. Analytical chemistry always depends on the chemical equation connecting the measured reagent to the analyte.
This is why titration questions should be approached slowly:
What substance was in the burette?
What substance was in the aliquot?
What is the balanced equation?
What is the mole ratio?
What volume of the original sample does the aliquot represent?
Each answer depends on those steps.
Hypotheses had to be evaluated against results
Karolina’s hypothesis was that boiling would remove 75% of the oxalate compounds in spinach leaves.
The report noted that students needed to recognise that 75% was the predicted outcome and then compare their calculated percentage reduction with that prediction.
The calculated reduction was 60%.
That means the result did not support the hypothesis as stated, because the reduction was lower than the predicted 75%.
This is an important scientific reasoning point.
A hypothesis is not evaluated by whether the result sounds large or small. It is evaluated by comparison with the predicted outcome.
The number must be interpreted in relation to the claim.
Experimental contamination affected the titre
Question 6g asked students to explain the effect of residual water remaining on the outside of the spinach leaves.
The report noted that strong responses recognised that residual water could add soluble oxalate ions into the analysis. This would mean more permanganate was required, producing a larger titre.
This question is a good example of cause-and-effect experimental reasoning.
The water itself is not the analyte. The issue is that it may carry dissolved oxalate ions into the sample, increasing the amount of oxalate measured. That then increases the amount of permanganate required to reach the endpoint.
A vague answer that “water dilutes the sample” would miss the direction of the effect.
The question required students to think chemically about what was being transferred.
Analytical observations needed careful language
The 2025 exam repeatedly rewarded students who described observations precisely.
For example:
- acidified dichromate changes from orange to green when an aldehyde is oxidised
- bromine solution changes from brown to colourless when it reacts with a carbon-carbon double bond
- sodium hydrogen carbonate produces bubbles only with carboxylic acids because carbon dioxide is formed
- a broader and lower melting point range suggests impurities
- a colour-change endpoint may involve subjective judgement and random error
These observations are not interchangeable.
Each test has a specific chemical basis. A colour change alone is not meaningful unless students know which reagent is changing and why.
Analytical chemistry combined multiple sources of evidence
One of the strongest themes in the 2025 paper was that analytical chemistry often required evidence to be combined.
A compound’s identity might depend on:
- molecular formula
- functional group tests
- IR absorption bands
- mass spectrum peaks
- isotope patterns
- ¹³C NMR signals
- chemical shifts
- boiling point or melting point data
- reaction behaviour
No single piece of evidence always gives the whole answer.
High-scoring students build the structure or conclusion gradually. They ask what each piece of data eliminates and what it supports.
This is the analytical mindset VCE Chemistry rewards.
Why analytical chemistry errors happen
Analytical chemistry errors often happen because students choose techniques by memory rather than evidence.
They know bromine tests for double bonds, so they choose it even when both compounds contain double bonds. They know simple distillation separates liquids, but overlook that the boiling points are similar. They know melting point indicates purity, but forget impurities broaden and lower the range. They know titration involves concentration and volume, but forget the aliquot or mole ratio.
The 2025 exam rewarded students who asked whether the technique or calculation actually answered the question.
A method is only useful if it distinguishes the substances or measures the quantity being investigated.
What future Chemistry students should learn from 2025
The 2025 VCE Chemistry exam shows that analytical chemistry preparation must focus on evidence.
Students should be able to:
- interpret melting point range as evidence of purity
- choose functional group tests that distinguish compounds
- match separation techniques to boiling point and polarity
- read skeletal structures to determine molecular formulas
- interpret ¹³C NMR using carbon environments and symmetry
- identify functional groups from IR absorptions
- distinguish base peaks from molecular ion peaks
- use isotope patterns to infer atoms such as chlorine
- understand that isomers have the same molecular formula and molecular ion mass
- calculate titration results using aliquots, dilution factors and stoichiometry
- evaluate hypotheses by comparing results with predictions
- explain how contamination or residual solution affects titres
These skills make analytical chemistry one of the most important parts of the course.
It is not enough to know the technique.
Students must know what the technique proves.
How ATAR STAR approaches analytical chemistry
At ATAR STAR, analytical chemistry is taught as chemical evidence.
Students learn to interpret spectra, chromatograms, titration data, melting points, functional group tests and experimental observations as clues that support or eliminate possible conclusions. They practise linking each piece of evidence to the structure, concentration, purity or reaction being investigated.
The 2025 Examination Report confirms why this matters. High-scoring responses did not simply name techniques.
They used analytical evidence to make chemical conclusions.
That is what VCE Chemistry rewards.