How IB Chemistry Is Marked: Papers, IA and Lost Marks

IB Diploma Chemistry has a new course, first assessed in 2025. The content is now organised around two ideas, structure and reactivity, and experimental work is now tested directly in the written exam. If you are revising from older past papers, it is worth knowing exactly what the current exam looks like, and how its markschemes decide which answers earn credit.

The details below come from the IB’s Chemistry guide for first assessment 2025 and the May 2025 markschemes. Your teacher and the subject guide are the final word for your session.

The course: structure and reactivity, SL and HL

The syllabus is split into two strands. Structure covers the particulate nature of matter, models of bonding and structure, and the classification of matter. Reactivity covers what drives chemical reactions, how much, how fast and how far they go, and the mechanisms of chemical change. Questions often join the two, so expect an energetics calculation to lean on bonding, or a mechanism question to lean on structure.

HL students study everything at SL plus additional higher level material. The IB recommends 150 teaching hours for SL and 240 for HL, and the papers reflect that: they are longer and carry more marks at HL.

How the assessment is weighted

The weighting is the same at SL and HL. External exams make up 80% of the final grade and the internal assessment the other 20%:

• Paper 1 – 36%. SL 1 hour 30 minutes, 55 marks; HL 2 hours, 75 marks.
• Paper 2 – 44%. SL 1 hour 30 minutes, 50 marks; HL 2 hours 30 minutes, 90 marks.
• Internal assessment (the scientific investigation) – 20%, marked out of 24.

A calculator is permitted in both papers, and every student has a clean copy of the Chemistry data booklet.

Paper 1: 1A and 1B

Paper 1 comes as two separate booklets, completed together in one sitting.

Paper 1A is multiple choice: 30 questions for 30 marks at SL, and 40 questions for 40 marks at HL. No marks are deducted for incorrect answers, so never leave a question blank. The wrong options are written to catch half-learned ideas, so test each option as a statement rather than picking the first that looks familiar.

Paper 1B is worth 25 marks at SL and 35 at HL, and contains data-based questions and questions on experimental work. Expect to read values from tables and graphs, process data, choose apparatus, and say how you would carry out a procedure precisely. In the May 2025 HL paper, for example, marks went to describing how to make up a standard solution step by step: dissolve the solid in distilled water, make up to the mark in a volumetric flask, then invert to mix. Practical detail of that kind is only learned by doing the practicals and noticing what you did.

Paper 2: short answers and extended responses

Paper 2 contains short-answer and extended-response questions across the syllabus, worth 50 marks at SL and 90 at HL. HL papers include the additional higher level material. It is the largest single component of the grade at 44%, and it is where calculation technique, equations and mechanisms carry the most weight.

The internal assessment

The internal assessment is a scientific investigation: an open-ended task in which you gather and analyse data to answer a research question you have formulated yourself. It is written up as a report of no more than 3,000 words, and the IB recommends around 10 hours of teaching time for it. Data tables, graphs, equations, calculations and references do not count towards the word limit.

It is marked out of 24 against four criteria, each worth 6 marks: research design, data analysis, conclusion and evaluation. Your teacher marks it and the IB moderates the marks. Because each criterion is a quarter of the IA, a strong method cannot rescue a thin evaluation; give all four the same care. The course also includes the collaborative sciences project, in which students work across science subjects on a shared problem.

How IB chemistry markschemes work

Every IB chemistry markscheme opens with the same set of marking notes. Knowing them changes how you write:

• Marks are awarded point by point. Each marking point earns a tick, and notes often refer to them as M1, M2 and so on. A part marked “max” has more acceptable points than marks, so make distinct points rather than one point several ways.
• Correct final answers can earn full marks. Many calculations carry a note such as “Award [2] for correct final answer”. But some notes say a later mark cannot be given without working for the earlier one, so always show the steps. That is also what the command term calculate asks for: a numerical answer showing the relevant stages in the working.
• Error carried forward (ECF). If you get an early value wrong and use it correctly later, the later marks can still be awarded. The same principle as method marks at GCSE: a wrong first step does not have to cost the whole question.
• Units and significant figures are not penalised unless the markscheme notes say so. You cannot see the notes in the exam, so give units and a sensible number of significant figures every time.
• Name or formula, as asked. If a question asks for the name of a substance, a correct formula does not earn the mark unless the notes allow it, and the reverse is also true.
• Equations must be balanced symbol equations. A word equation or an unbalanced equation does not usually score. State symbols are ignored by default, unless the question or notes require them, and some do.
• Underlined words are essential. If a word is underlined in the markscheme, the mark is not awarded without it. Equivalent wording is otherwise accepted, often noted as OWTTE (“or words to that effect”).

Where marks are lost

Most IB chemistry marks that slip away do so for the same few reasons.

• Signs in energetics. In the May 2025 HL Paper 2 markscheme, an enthalpy change with the right size but the wrong sign was capped below full marks. Decide whether a reaction is exothermic or endothermic, and check that your sign agrees.
• Missing the command term. IB uses its own command terms. State wants a brief answer with no explanation; explain wants reasons or causes; deduce wants a conclusion from the information given. The same thinking applies as with GCSE command words.
• Mechanisms drawn loosely. Curly arrows are marked on where they start and where they end: from the C=C bond, from a lone pair or negative charge. An arrow that starts in the wrong place can cost the mark even when you know the mechanism.
• Vague practical answers. “Use accurate equipment” earns nothing. Name the apparatus (a volumetric pipette, a burette) and say what you do with it.
• Losing the thread in multi-step calculations. Write each step on its own line with a label, such as moles of HCl, then limiting reagent. If one step goes wrong, ECF can only rescue the rest if the examiner can follow it.

How to practise

These habits are learned by writing answers and finding out exactly which marking points they earned. On Exaim, every written answer is marked against the markscheme point by point, so you can see that you had the right method but dropped the sign, or named the reagent when the question asked for a formula, and fix it on the next attempt.

IB Chemistry is available at both levels. Start with the free revision notes, flashcards, mind maps and worksheets for IB Chemistry HL or IB Chemistry SL, organised by topic and subtopic, or browse every course from the revision resources page.