An IB Chemistry IA kinetics investigation should examine how a clearly defined variable affects reaction rate, using a method that produces sufficient quantitative data for meaningful analysis. Strong options include an iodine clock reaction, the catalytic decomposition of hydrogen peroxide, and the effect of concentration or temperature on sodium thiosulfate reactions.
The topic itself does not need to be unusual. A familiar reaction can support an excellent scientific investigation if the research question is focused, the endpoint is measured consistently, variables are controlled, uncertainties are addressed, and the analysis goes beyond simply stating that the reaction became faster.
What the current IB Chemistry IA requires
Under the current IB Chemistry course, the internal assessment is called the scientific investigation. It is an open-ended investigation in which you collect and analyse data to answer your own research question. The report has a maximum overall word count of 3,000 words, and the scientific investigation contributes 20% of the final Chemistry grade at both SL and HL.
The four assessment criteria are:
Research design
Data analysis
Conclusion
Evaluation
Each criterion is worth 6 marks. This means half of the available marks come from the conclusion and evaluation, so collecting data is only the beginning. You must interpret the chemical significance of the results, compare them with accepted scientific theory where possible, and explain how specific methodological limitations affected the findings.
The IB allows limited collaboration in small groups when appropriate. Students may use similar methodologies, but each student must have a distinct independent or dependent variable and collect unique data. Every student submits an individual report.
A manageable IA normally changes one independent variable across a suitable numerical range. Investigating several factors at once often creates an unnecessarily complicated design and makes it difficult to isolate cause and effect.
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Investigation
Possible independent variable
Rate measurement
Useful analysis
Iodine clock reaction
Iodide, persulfate or hydrogen peroxide concentration
Time to blue-black endpoint
Relative initial rate and reaction order
Iodine clock reaction
Temperature in kelvin
Time to endpoint
Arrhenius plot and activation energy
Hydrogen peroxide decomposition
Concentration of one homogeneous catalyst
Oxygen volume against time
Initial gradient or rate constant
Hydrogen peroxide decomposition
Temperature
Oxygen volume against time
Initial rate and Arrhenius relationship
Sodium thiosulfate and acid
Thiosulfate concentration
Time for a cross to disappear
Relative rate and possible reaction order
Sodium thiosulfate and acid
Temperature
Time for sulfur cloudiness endpoint
Relative rate and temperature dependence
These are starting points rather than finished research questions. Before committing to one, conduct a pilot study to check that the reaction is neither effectively instantaneous nor so slow that temperature drift and evaporation become serious problems.
The RevisionDojo collection of Chemistry IA examples can help you compare the scope and analysis of different investigations. It should be used to study scientific structure, not to copy another student's question or method.
Iodine clock reaction IA ideas
An iodine clock is effective because it creates a clear endpoint. In one common system, iodine is produced by the oxidation of iodide ions. Added thiosulfate ions initially consume the iodine:
I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq)
Once the fixed amount of thiosulfate has been consumed, iodine forms a blue-black complex with starch. If the thiosulfate amount and total reaction volume remain constant, the colour appears after approximately the same amount of iodine has formed in every trial. The reciprocal of the endpoint time, 1/t, can therefore be used as a relative rate, provided the assumptions behind that approximation are explained.
Possible research questions include:
How does initial iodide concentration affect the relative initial rate of the persulfate-iodide clock reaction at constant temperature?
How does persulfate concentration affect the rate, and what is the reaction order with respect to persulfate?
How does temperature affect the rate of an iodine clock reaction, and what activation energy can be estimated from an Arrhenius plot?
For a concentration investigation, keep the total volume constant by replacing removed reactant solution with distilled water. This prevents dilution and optical depth from changing unintentionally. Temperature, starch quantity, thiosulfate amount, mixing procedure and the time between mixing and starting the timer must also be controlled.
The Royal Society of Chemistry's iodine clock practical illustrates the endpoint chemistry and necessary safety precautions. Its classroom recipe should still be adapted through piloting and a school-approved risk assessment.
Investigating catalyst effects
The decomposition of hydrogen peroxide is a common catalyst investigation:
2H₂O₂(aq) → 2H₂O(l) + O₂(g)
Rate can be measured by recording oxygen volume with a gas syringe or pressure sensor at short, regular intervals. Plot oxygen volume against time and calculate the initial rate from the gradient near the start, rather than using only the final gas volume. A catalyst should change the rate by providing an alternative pathway with lower activation energy, but it should not change the theoretical final amount of product when the limiting reactant is unchanged.
A focused research question might ask how the concentration of iron(III) ions affects the initial rate of hydrogen peroxide decomposition at a fixed peroxide concentration and temperature. This is usually easier to interpret than comparing unrelated catalysts such as manganese dioxide, iodide ions and catalase, because different catalysts have different active species, mechanisms and appropriate concentration units.
If using a solid catalyst, surface area becomes a major confounding variable. Equal masses of powder and granules do not expose equal catalytic areas. A homogeneous dissolved catalyst can therefore provide cleaner quantitative control, although its chemical hazards and disposal requirements must still be assessed.
Concentration and temperature investigations
The reaction between sodium thiosulfate and acid produces solid sulfur, which progressively obscures a black cross:
S₂O₃²⁻(aq) + 2H⁺(aq) → S(s) + SO₂(g) + H₂O(l)
A concentration investigation can vary sodium thiosulfate concentration while keeping acid concentration, total volume, temperature and viewing conditions constant. The Royal Society of Chemistry's concentration and reaction-rate practical demonstrates this disappearing-cross method.
The method is accessible but subjective. The apparent endpoint depends on the observer, lighting, cross thickness, flask geometry and viewing distance. A light sensor or colorimeter can replace visual judgement by defining a numerical transmittance or absorbance threshold, substantially improving reproducibility.
Temperature investigations can provide deeper analysis through the Arrhenius equation:
ln k = -Ea/R(1/T) + ln A
If relative rate is proportional to the rate constant under otherwise identical conditions, plotting ln(1/t) against 1/T, with temperature in kelvin, should produce an approximately linear relationship. The gradient equals -Ea/R, allowing an experimental activation energy to be estimated. All reactant solutions should equilibrate in the water bath before mixing, and the actual reaction temperature should be measured rather than assuming it equals the bath setting.
How to measure reaction rate properly
Choose the rate method before finalising the research question. Your dependent variable should describe what is actually measured and how it is converted into rate.
Clock or fixed-endpoint method
A clock method records the time required to produce a fixed amount of product. The quantity 1/t has units of s⁻¹ and is a relative rate, not automatically a concentration rate in mol dm⁻³ s⁻¹. To calculate an absolute average rate, you need the known concentration change at the endpoint.
Continuous monitoring
Gas syringes, pressure sensors, balances, colorimeters and spectrophotometers generate measurements throughout the reaction. Continuous data allow you to inspect the curve, calculate an initial gradient and identify whether the rate changes over time. Sensors should be calibrated or checked, and their sampling interval and resolution should be reported.
Initial-rate analysis
For concentration studies, a general rate relationship may be written as:
rate = k[A]ᵐ[B]ⁿ
Changing one reactant concentration while holding the other constant allows its order to be investigated. A plot of ln(rate) against ln[A] has gradient m, but this analysis is defensible only if the initial-rate approximation and concentration calculations are valid.
Controls, repeats and data quality
Use at least five well-spaced independent-variable levels as a practical planning guideline, not an official IB rule. Three to five repeats per level are often appropriate, although the final number should follow your pilot data, available time and observed variation.
Important controls commonly include:
Temperature: use a thermostatically controlled water bath where possible.
Total volume: keep it constant when changing concentration by dilution.
Mixing: standardise stirring speed, duration and order of addition.
Endpoint conditions: keep lighting, vessel geometry and sensor threshold unchanged.
Reactant source: use the same stock solutions throughout the experiment.
Catalyst properties: control catalyst concentration, mass and exposed surface area.
Record every raw measurement with its unit and absolute uncertainty. Show individual repeats rather than only the mean, identify anomalies using scientific reasoning, and do not remove inconvenient values without justification. Useful processed quantities may include mean rate, standard deviation, percentage uncertainty, gradient uncertainty and an appropriate regression measure.
Common mistakes to avoid
Changing two variables together: increasing both concentration and temperature prevents a valid causal conclusion.
Calling 1/t an absolute rate: it is normally a relative rate unless the endpoint concentration change is known.
Using too narrow a range: genuine changes can become indistinguishable from experimental uncertainty.
Ignoring the start delay: manual mixing and stopwatch reaction time can dominate very fast trials.
Listing generic errors: “human error” does not explain the direction or likely magnitude of an effect.
Overclaiming from R²: a high coefficient of determination does not prove a mechanism or remove systematic error.
Proposing unrealistic improvements: recommend specific equipment or procedural changes that your school could plausibly implement.
A strong evaluation links each limitation to its effect. For example, delayed timer activation makes recorded times too short, disproportionately inflating calculated 1/t values for the fastest reactions. A light sensor with automated data logging would reduce endpoint subjectivity, but it would not remove uncertainties in concentration or temperature.
Turning an idea into a focused research question
A useful structure is:
How does [quantified independent variable and range] affect [defined rate measurement] for [specified reaction] under [important controlled conditions]?
For example: “How does the initial potassium iodide concentration from 0.0200 to 0.100 mol dm⁻³ affect the relative initial rate, measured as the reciprocal of the time to a fixed starch-iodine endpoint, in the persulfate-iodide reaction at 298 K?”
Pilot the method before fixing the range. Then use chemical kinetics study notes to check the underlying theory and the IB Chemistry IA Grader to review whether the report addresses all four criteria. Jojo AI can help pressure-test a research question or identify uncontrolled variables, but your scientific decisions, data and final writing must remain your own.
Conclusion
The strongest kinetics IAs combine a manageable reaction with precise measurement and analysis matched to the research question. Iodine clocks are well suited to concentration, reaction-order and temperature studies; hydrogen peroxide decomposition supports continuous gas measurements and catalyst investigations; and sodium thiosulfate offers an accessible concentration or temperature experiment if endpoint subjectivity is controlled.
Prioritise a successful pilot, one independent variable, consistent controls, sufficient repeats and honest uncertainty analysis. RevisionDojo's Chemistry IA examples, kinetics notes and rubric-based IA Grader can then help you check the scientific depth and presentation of your own investigation.
Daniel holds an MSc in Chemistry from Imperial College London and has taught IB Chemistry for over 20 years, including as Head of Chemistry. His focus is on building the conceptual understanding behind each equation rather than rote recall.
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