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Subject guide

IB Chemistry Internal Assessment guide

Written and cross-checked by IB Diploma graduates: Alexander (41), Alejandro (40), Martina (40), Victoria (38), Martin (35), Maria (34)

Last reviewed: September 2026 · Checked against official IB guidance · Editorial policy

The IB Chemistry Scientific Investigation (IA) is graded against 4 IB assessment criteria worth 24 marks. This guide explains the mark scheme for each criterion and what the published criteria reward at each score level at Higher Level (HL) and Standard Level (SL).

At a glance

Syllabus: First assessment May 2025
Word limit: 3,000 words maximum
Marks: 24 (4 criteria × 6)
Weighting: 20% of the final grade
SL / HL: Same criteria at SL and HL

Word count

3,000 words maximum. See the IA word limits hub for what counts. IA word limits by subject →

How the scientific investigation is structured

Map your report sections to the four criteria. Examiners score each criterion independently — a strong method cannot rescue weak analysis.

Introduction & context → Criterion A (research design): research question, variables, background theory, reproducible method, controls, safety/ethics.
Data & processing → Criterion B (data analysis): tables/graphs with units and sig figs, uncertainties, statistics aligned to the question.
Conclusion → Criterion C: answer the RQ using processed data, compare to published values or theory.
Evaluation → Criterion D: specific weaknesses, their impact, realistic improvements.

Worked mini-example (enzyme investigation)

Research question: How does temperature (10–50 °C) affect catalase activity in potato extract, measured as O₂ volume in 60 s?

Weak method sketch

“I changed temperature and measured gas.” No enzyme mass control, no H₂O₂ freshness, no repeats — cannot reach band 5–6 on Criterion A.

Stronger method sketch

Fixed potato mass, fresh 3% H₂O₂, water-bath equilibration, 5 temperatures × 5 trials, same timer — reproducible with stated uncertainties.

Analysis: plot rate vs temperature, identify optimum, discuss denaturation above ~40 °C. Compare to literature kinetics. Evaluation: name heat-loss to bath, timing reaction start, and whether SD or SEM is appropriate for error bars.

Chemistry-specific execution notes

Reaction choice: disappearing cross, gas collection, or colorimetry — pick one where concentration is the only intentional change.
Uncertainty: propagate percentage uncertainty in rate; distinguish random scatter from systematic error (e.g. clock reaction delay).
Calibration: if using colorimetry, include a calibration curve with R² stated.
Significant figures: match SF in processed results to the least precise measurement.
Biggest trap: stock solution evaporation changing concentration between trials.

Ready-made research questions with feasibility notes: chemistry IA ideas →

4 criteria24 marks totalSL & HL available

IB assessment criteria

Each criterion is presented independently using the configured mark-band descriptors for this subject and assessment session.

Criterion	Name	Marks
Research Design	Research Design	6
Data Analysis	Data Analysis	6
Conclusion	Conclusion	6
Evaluation	Evaluation	6
Total		24

Criterion-by-criterion breakdown

Research Design

0-6

What this criterion assesses

A research question described within a specific and appropriate context: variables (or correlated variables), the system it sits in, and directly relevant background theory. Methodological considerations explained — how variables are measured, scope and quality of the data, control variables, and safety/ethical/environmental issues. Enough procedural detail that the investigation could be reproduced.

Mark band descriptors

Criterion A: Research design (0–6):
- 0: The report does not reach the standard described by the descriptors below.
- 1–2: The research question is stated without context. Methodological considerations associated with collecting data relevant to the research question are stated. The description of the methodology for collecting or selecting data lacks the detail to allow for the investigation to be reproduced.
- 3–4: The research question is outlined within a broad context. Methodological considerations associated with collecting relevant and sufficient data to answer the research question are described. The description of the methodology for collecting or selecting data allows for the investigation to be reproduced with few ambiguities or omissions.
- 5–6: The research question is described within a specific and appropriate context. Methodological considerations associated with collecting relevant and sufficient data to answer the research question are explained. The description of the methodology for collecting or selecting data allows for the investigation to be reproduced.
Note: A research question with context should contain reference to the dependent and independent variables (or two correlated variables), a concise description of the system in which the research question is embedded, and background theory of direct relevance.

Common mistakes

Research question stated without context, variables or background theory
Method missing the detail needed to reproduce the investigation
Control variables not identified, or how they were controlled not explained
Safety, ethical or environmental issues ignored

Data Analysis

0-6

What this criterion assesses

Recording and processing of data communicated both clearly and precisely — correct conventions for tables, graphs, units, decimal places and significant figures — with appropriate consideration of uncertainties, and processing relevant to the research question carried out appropriately and accurately.

Mark band descriptors

Criterion B: Data analysis (0–6):
- 0: The report does not reach a standard described by the descriptors below.
- 1–2: The recording and processing of the data is communicated but is neither clear nor precise. The recording and processing of data shows limited evidence of the consideration of uncertainties. Some processing of data relevant to addressing the research question is carried out but with major omissions, inaccuracies or inconsistencies.
- 3–4: The communication of the recording and processing of the data is either clear or precise. The recording and processing of data shows evidence of a consideration of uncertainties but with some significant omissions or inaccuracies. The processing of data relevant to addressing the research question is carried out but with some significant omissions, inaccuracies or inconsistencies.
- 5–6: The communication of the recording and processing of the data is both clear and precise. The recording and processing of data shows evidence of an appropriate consideration of uncertainties. The processing of data relevant to addressing the research question is carried out appropriately and accurately.
Note: "Clear" means the method of processing can be understood easily; "precise" means conventions are followed correctly (annotation of graphs and tables, units, decimal places, significant figures).

Common mistakes

Tables or graphs missing units, labels or consistent significant figures
Uncertainties ignored or treated superficially
Processing steps that can't be followed or contain errors
Processed results that don't address the research question

Conclusion

0-6

What this criterion assesses

A conclusion justified by the analysis — including the interpretation of processed data and its uncertainties — that answers the research question, and is justified through relevant comparison to the accepted scientific context (published values, theory), with traceable citations.

Mark band descriptors

Criterion C: Conclusion (0–6):
- 0: The report does not reach a standard described by the descriptors below.
- 1–2: A conclusion is stated that is relevant to the research question but is not supported by the analysis presented. The conclusion makes superficial comparison to the accepted scientific context.
- 3–4: A conclusion is described that is relevant to the research question but is not fully consistent with the analysis presented. A conclusion is described that makes some relevant comparison to the accepted scientific context.
- 5–6: A conclusion is justified that is relevant to the research question and fully consistent with the analysis presented. A conclusion is justified through relevant comparison to the accepted scientific context.
Note: A fully consistent conclusion requires the interpretation of processed data including associated uncertainties. Scientific context refers to published material, published values, course notes or textbooks, cited in enough detail to be traceable.

Common mistakes

Conclusion claims more than the data can support
No comparison with published values or accepted theory
Uncertainties ignored when interpreting the result
Sources cited too vaguely to be traceable

Evaluation

0-6

What this criterion assesses

Specific methodological weaknesses and limitations explained — including their relative impact on the results — with realistic improvements that directly address the identified weaknesses.

Mark band descriptors

Criterion D: Evaluation (0–6):
- 0: The report does not reach a standard described by the descriptors below.
- 1–2: The report states generic methodological weaknesses or limitations. Realistic improvements to the investigation are stated.
- 3–4: The report describes specific methodological weaknesses or limitations. Realistic improvements to the investigation, that are relevant to the identified weaknesses or limitations, are described.
- 5–6: The report explains the relative impact of specific methodological weaknesses or limitations. Realistic improvements to the investigation, that are relevant to the identified weaknesses or limitations, are explained.
Note: "Generic" means general to many methodologies rather than specific to this investigation. Weaknesses could relate to the control of variables, the precision of measurement or the variation in the data; limitations could refer to the range of data collected, the confines of the system or the applicability of assumptions made.

Common mistakes

Generic weaknesses ("human error") not specific to this methodology
Improvements unrelated to the weaknesses identified
No discussion of how much each weakness affects the conclusion
Limitations of scope or of assumptions not considered

Sources & verification

Primary-source references used to verify key assessment facts on this page. Last source check: September 22, 2026.

The exact subject guide for Chemistry is the authority for the task, criteria and limits. Some IB subject guides do not have a stable public URL, so this page names the configured assessment session and links the official IB update hubs instead of fabricating a direct source link.

IB — Diploma Programme assessment and examsOfficial overview of criterion-related assessment and internal assessment in the Diploma Programme.
IB — current curriculum updatesOfficial update hub for subject and first-assessment changes. Use it to confirm that your exam session matches the criteria shown here.

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