IB Chemistry IA: design, uncertainties and evaluation

What each criterion looks for in chemistry

Teachers' guidance says charts, diagrams, data tables, equations, calculations, headings and references do not count towards the 3,000 words.

Questions that work in a school lab

Strong chemistry questions change one variable over a useful range and measure one quantity precisely. Examples of the type: how the concentration of a reactant affects the initial rate of a reaction measured by a colour change or gas volume; how temperature affects the enthalpy change measured in a simple calorimeter; how the concentration of vitamin C in a fruit juice changes with storage time, measured by titration. Each names the variable, its range and the method.

Check feasibility before you commit: the school must have the chemicals and equipment, the reaction must be safe in a school lab, and each trial must be short enough for several repeats in about 10 hours. Database and simulation investigations are also allowed, such as analysing published thermodynamic data, but they need the same focused question.

Worked example: propagating uncertainty in a titration

Invented data. 25.00 cm^3 of hydrochloric acid is titrated with 0.100 mol dm^-3 sodium hydroxide; the mean titre is 24.50 cm^3. Find the acid concentration with its uncertainty.

1. Concentration: HCl and NaOH react 1 : 1, so c(HCl) = 0.100 × 24.50 ÷ 25.00 = 0.0980 mol dm^-3.
2. Burette: each reading is ±0.05 cm^3 and a titre is the difference of two readings, so the titre uncertainty is ±0.10 cm^3. Percentage: 0.10 ÷ 24.50 × 100 = 0.41%.
3. Pipette: 25.00 ± 0.06 cm^3. Percentage: 0.06 ÷ 25.00 × 100 = 0.24%.
4. NaOH concentration: 0.100 ± 0.001 mol dm^-3. Percentage: 1.0%.
5. When quantities are multiplied or divided, add percentage uncertainties: 0.41 + 0.24 + 1.0 = 1.65%, about 1.6%.
6. Absolute uncertainty: 0.0980 × 0.0165 = 0.0016, so c(HCl) = 0.098 ± 0.002 mol dm^-3. The answer and its uncertainty are given to the same decimal place.
7. Check: the largest contribution is the NaOH concentration, not the glassware. That is a useful evaluation point: standardising the NaOH would improve the result more than a better burette.

Where Chemistry IA marks are lost

• Recording uncertainties in raw data but not carrying them through the calculations.
• A method that says "add some acid" instead of volumes, concentrations, apparatus and the order of steps.
• Too few data points to show a trend, or a range so narrow that the change is within the uncertainty.
• A conclusion that describes the graph without explaining it with chemistry or comparing it with a literature value.
• Percentage error against a literature value reported without asking whether it is larger than the total uncertainty, which is how you tell systematic error from random error.
• Improvements such as "use better equipment" rather than specific changes and their expected effect.

How one-to-one lessons help with the Chemistry IA

A tutor who teaches IB Chemistry helps the student test a question for feasibility, think through the variables and controls, and understand the chemistry behind the expected result. When the data exists, lessons cover the skills examiners reward: uncertainty propagation, significant figures, choosing and plotting graphs, gradients and intercepts, and comparing results with literature values, practised on the shared whiteboard with the student's own numbers.

The IA is assessed as the student's own work, and teachers give only limited feedback on a draft. A tutor never writes or edits the report; the student designs, carries out and writes the investigation.