NCEA 91391: organic compounds (Level 3 Chemistry)

What NCEA 91391 assesses

NZQA limits the compounds in the standard (version 2) to those with one or more of these functional groups: alkene, haloalkane, amine, alcohol, aldehyde, ketone, carboxylic acid, ester (including triglycerides), acyl chloride and amide. The standard covers:

• naming with IUPAC conventions (no more than eight carbons in the longest chain) and drawing structural formulae
• structure, including functional groups, constitutional isomers and stereoisomers
• substitution reactions, including esterification, condensation, hydrolysis and polymerisation
• oxidation with MnO₄⁻/H⁺, Cr₂O₇²⁻/H⁺, Tollens', Fehling's and Benedict's reagents, and reduction of aldehydes and ketones with NaBH₄
• elimination reactions, including major and minor products, and addition reactions of alkenes
• polyesters and polyamides, including proteins
• physical properties used to tell compounds apart: solubility, melting and boiling points, and the rotation of plane-polarised light

The three grades go up in steps. Achieved names and draws organic compounds and gives an account of their physical properties and reactivity. Merit makes and explains links between structure, functional groups, physical properties and reactivity. Excellence elaborates, justifies, relates, evaluates or compares and contrasts those links. Every grade needs correct chemistry vocabulary, symbols and conventions, and Excellence needs them used consistently. NZQA's 2025 report says that at Excellence you need to apply ideas in unfamiliar contexts and read each question for what it asks, not for what you hoped it would ask.

The NCEA 91391 exam in 2026 and 2027

NCEA 91391 is one of three Level 3 Chemistry externals, with 91390 (thermochemistry) and 91392 (equilibrium in aqueous systems). The 2026 exam is on Friday 20 November, in the afternoon session. NZQA's specifications for both years say the exam is on printed paper and 91391 is a 5-credit external.

• Three questions: you answer all three. The format is the same for each Level 3 Chemistry standard, and the questions may be set in contexts that are unfamiliar to you.
• Calculator: an approved scientific or graphics calculator is required.
• Resource booklet: it has the formulae you need, such as n = cV, a periodic table with symbols, atomic numbers and molar masses, and a list of nine complex ions with their formulae.
• Calculations: show all working, use an appropriate number of significant figures (usually three) and include the correct units.
• Practical work: NZQA says you should be familiar with relevant practical work, and the content is set by the explanatory notes of each standard.
• Specific points: naming of amines is restricted to primary amines, you are not expected to recall common names of amino acids, and NZQA says knowledge of the Level 2 standard AS91165 will be assumed.

How NCEA 91391 is marked

The paper has three questions, each scored N0 to E8 and added to a total out of 24. Each question builds towards extended reasoning: NZQA's report says 2025 asked about optical isomers, reaction schemes, reflux and distillation, identifying unknowns, dipeptides and polyesters.

NCEA 91391 cut scores

Merit moved between 13 and 15 and Excellence between 19 and 20, with 2023 the highest of the five years. The scores are where each grade begins, out of 24.

Cut scores 2025

2025 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2024.

Cut scores 2024

2024 schedule: Achieved from 8, Merit from 14, Excellence from 19. Compared with 2023, Merit came down by 1 and Excellence came down by 1.

Cut scores 2023

2023 schedule: Achieved from 8, Merit from 15, Excellence from 20. Compared with 2022, Excellence went up by 1.

Cut scores 2022

2022 schedule: Achieved from 8, Merit from 15, Excellence from 19. Compared with 2021, Merit went up by 2.

Cut scores 2021

2021 schedule: Achieved from 8, Merit from 13, Excellence from 19.

Worked examples at each grade

Achieved: functional groups and optical isomers

Butan-2-ol, CH₃CH(OH)CH₂CH₃, has one carbon that carries four different groups: H, OH, CH₃ and C₂H₅. This asymmetric carbon makes the molecule chiral, so it has two non-superimposable mirror images, called enantiomers. They rotate plane-polarised light by equal amounts in opposite directions. Butan-1-ol has no asymmetric carbon and no optical isomers.

Merit: a multi-step scheme and the apparatus

Butan-1-ol is oxidised by acidified dichromate, Cr₂O₇²⁻/H⁺. The first product is butanal and the second is butanoic acid:

• Butan-1-ol to butanal: heat gently and distil off the butanal as it forms. The aldehyde has a lower boiling point than the alcohol because it cannot form hydrogen bonds with itself, so it leaves the flask before it can be oxidised further.
• Butan-1-ol to butanoic acid: heat under reflux. The condenser is vertical, so vapours condense and fall back into the flask, and the butanal stays in contact with the oxidant until it becomes the acid.

The colour changes from orange to green as Cr₂O₇²⁻ is reduced. NZQA's 2025 report says Merit candidates explained distillation and reflux with reference to boiling points and the position of the condenser, and that Excellence candidates distinguished between them clearly.

Excellence: identifying three unknown liquids

Three colourless liquids are known to be butanal, butanone and butanoic acid. Plan the tests and justify the order. Butanal and butanone are isomers (C₄H₈O), so their physical properties are close, and tests on their functional groups work better:

• Add sodium carbonate solution. Only butanoic acid fizzes, as carbon dioxide forms. That identifies the acid and removes it from the set.
• Warm the other two with Tollens' reagent. Butanal is oxidised and the silver ions are reduced to a silver mirror. Butanone has no hydrogen on the carbonyl carbon, so it cannot be oxidised and gives no change.

Excellence justifies the order, uses more than one piece of evidence for each liquid, and states observations with start and end colours. The same standard includes condensation: two amino acids join with the loss of a water molecule to make a dipeptide with a peptide link, and hydrolysis of a polyester breaks its ester links with water to give the alcohol and the carboxylic acid it came from.

Now name organic families in our Organic Chemistry course, then press Mark to check your answer in the course:

Exam answers

The answers and a worked mark scheme come with today's paper once it is marked. We do not publish official or past paper answers. Every question on the daily paper is our own.

Use the daily paper as a practice exam

The Level 3 Chemistry track above is a short timed mock of 8 questions, not a full exam and not written by NZQA (NCEA Level 3 Chemistry). It covers amines, amino acids and polymers, carbonyl compounds and organic synthesis, which support 91391. It also includes NMR, aromatic chemistry and transition metals, which are not part of 91391, so treat those as extra. For the Level 2 organic chemistry that this standard assumes, see NCEA 91165.

Is NCEA 91391 changing?

NZQA's 2027 specification repeats this standard unchanged and still assumes the Level 2 organic standard. Year 13 will move to NZACE in 2030.

Common mistakes in NCEA 91391

• Structures with wrong bonding. NZQA's 2025 report lists incorrect bonding and misplaced functional groups as a Not Achieved error.
• Leaving reaction schemes unfinished. Complete each step with reagents and the organic product.
• Confusing distillation and reflux. Say where the condenser is and what it does to the products.
• Answers that are too brief. Justify identifications and outcomes, and link reaction conditions to products.
• One piece of evidence. Use several observations to justify an identification.

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