QCE Chemistry IA2 Student Experiment: 2026 guide

What IA2 is

IA2 is the Student Experiment, a QCAA-mandated internal assessment in Unit 3 (continuing into early Unit 4). Students modify or extend an existing chemistry investigation, conduct it, analyse the data, and report.

The deliverable is a scientific report of up to 10 pages including diagrams. Worth 20 percent of the subject result, the largest of the three internal assessments.

Assessment criteria

QCAA's four IA2 criteria:

1. Research and Planning. Quality of the research question, hypothesis, methodology, identification of variables, justification of choices.
2. Analysis of Evidence. Quality of data collection, tabulation, processing, graphing, uncertainty.
3. Interpretation and Evaluation. Quality of analysis, conclusion, evaluation of methodology, limitations, suggestions for improvement.
4. Communication. Scientific writing, structure, referencing.

Research question construction

A strong research question is specific and testable.

Components:

• Independent variable (what you vary).
• Dependent variable (what you measure).
• Range of values.
• Controlled variables (what you keep constant).
• Conditions (temperature, environment).

Example (rate). "How does the concentration of HCl (0.05, 0.10, 0.20, 0.30, 0.50 M) affect the initial rate of reaction with excess CaCO3 (1.00 g, 2 mm particles) at 25 degrees C, measured by mass loss?"

Example (equilibrium). "How does temperature (15, 25, 35, 45, 55 degrees C) affect the position of equilibrium of the iron(III) thiocyanate complex, measured by absorbance at 450 nm?"

Example (acid-base). "How does the structure of three organic acids (methanoic, ethanoic, propanoic) affect their dissociation constant Ka at 25 degrees C, measured by titration with 0.100 M NaOH?"

Methodology

A complete methodology includes:

1. Apparatus and reagents with quantities and uncertainties (50 mL volumetric flask plus or minus 0.05 mL).
2. Procedure as numbered steps reproducible by another student.
3. Risk assessment (hazards, controls).
4. Identification and control of variables.
5. Sample size: minimum 5 trials per condition; minimum 5 conditions.

Controls. Match temperature, particle size, reaction volume across all trials. Use the same brand of reagent. Calibrate instruments.

The classic IA2 redox-titration apparatus determines iron in commercial iron supplement tablets by titration against standardised potassium permanganate. The labelled diagram earns marks in the "research and planning" criterion.

A calibration curve underpins both UV-vis and AAS quantitative analyses. The straight line from the standards then converts the unknown's measured absorbance into a concentration.

Data collection

Tabulate raw data immediately with units, uncertainties, and sig fig consistent with instrument precision.

Repeat each measurement. Three replicates minimum per condition; five preferred. Reject outliers using the Q-test or by inspection (cite reasoning).

Process data. Calculate means and standard deviations. Derive quantities (rate from mass-time, Kc from equilibrium concentrations, Ka from titration data).

Graphing and regression

A graph should have:

• Title.
• Axis labels with units.
• Appropriate scale, gridlines.
• Data points with uncertainty bars.
• Line of best fit (or curve as warranted).
• Gradient and intercept with units.

Linear regression. Report slope, intercept, R squared. Slope often has chemical meaning (rate constant, Ka).

Non-linear data may need transformation. Rate versus 1/T gives the Arrhenius plot ($\ln k$ versus $1/T$).

Uncertainty analysis

QCAA expects propagation of uncertainty.

Rules:

• Absolute uncertainty for addition or subtraction.
• Percentage uncertainty for multiplication or division.
• Quote final answer with the same sig fig as the smallest sig fig in input.

Report each measurement's uncertainty from instrument precision (half the smallest division for analog, instrument spec for digital).

A QCAA "interpretation and evaluation" response that ranks error sources by impact and tags each as systematic or random beats one that lists vague "human error". Visualise the ranking as a horizontal bar plot.

Interpretation and evaluation

Interpretation. State the trend with specific numbers: "Initial rate increased from $2.4 \times 10^{-3}$ to $1.9 \times 10^{-2}$ mol/L/s as HCl concentration increased from 0.05 to 0.50 M, an approximately linear relationship suggesting first order in [HCl]."

Conclusion. Answer the research question. State the relationship and the chemistry that explains it.

Evaluation. Identify limitations of the method. Quantify their impact where possible. Suggest specific improvements: "The mass-loss method underestimates rate by not capturing CO2 dissolved in the solution; an inverted-cylinder gas collection apparatus would capture this and improve accuracy."

Compare with theoretical or accepted values where available. Calculate percentage error and discuss its sources.

Communication

QCAA marks scientific writing. Use:

• Third-person passive (in formal writing).
• Past tense for what was done.
• Present tense for general principles.
• Numbered sections (Introduction, Methodology, Results, Discussion, Conclusion).
• Captions on figures and tables.
• IUPAC nomenclature consistently.

Reference scientifically: APA or QCAA-prescribed style. Cite the source of any non-trivial method or value.

Common pitfalls

Research question too broad. "How does temperature affect the iron(III) thiocyanate reaction" is too broad; specify a range, a measurement method, and a condition.

Insufficient replicates. Three is the QCAA minimum; five is more defensible.

Methodology under-controlled. List every variable and how it is held constant.

Inadequate uncertainty analysis. Quote uncertainties on every measurement and propagate.

Conclusion divorced from data. The conclusion must cite specific numerical findings and link them to the research question.

Discussion limited to listing errors. Evaluate their direction and magnitude. Suggest specific improvements.

Timeline

Week -8 (start of IA2 period). Identify topic, draft research question with teacher feedback.

Week -7. Finalise research question. Begin methodology draft.

Weeks -6 to -4. Conduct experiments. Refine method based on pilot results.

Weeks -3 to -2. Complete data collection and processing. Begin discussion.

Week -1. Draft full report. Get teacher draft-feedback.

Submission week. Polish, proofread, submit.

Check your knowledge

Six student-experiment process questions for IA2. These rehearse the moves a marker rewards: research-question refinement, controlled-variable identification, methodology justification, uncertainty propagation, and evaluation. ISMG criteria are signposted in the solutions. Three significant figures and units throughout.

1. A student proposes the research question "Does temperature affect rate of reaction?" Refine this into an IA2-grade question with a named chemistry context, a controlled IV with at least five values, and a measurable DV with appropriate precision. Justify each refinement. (4 marks)
2. A study investigates the effect of NaCl concentration on the equilibrium position of $[Co(H_2O)_6]^{2+} + 4Cl^- \rightleftharpoons [CoCl_4]^{2-} + 6H_2O$ in water-ethanol mixtures by colorimetry. List five controlled variables that must be held constant, and for each justify why with reference to the equilibrium expression or the colorimetric method. (5 marks)
3. The student measures the rate of $H_2O_2$ decomposition catalysed by potassium iodide at five $[KI]$ values (0.010, 0.025, 0.050, 0.075, 0.100 mol L$^{-1}$) by gas-volume collection over water. Initial-rate data ($\text{mL O}_2 \ \text{s}^{-1}$): 0.84, 2.10, 4.18, 6.32, 8.45. (a) State the expected relationship between rate and $[KI]$. (b) Calculate the gradient (rate constant) using the first and last data points. (c) Rank three sources of uncertainty in the measurement from largest to smallest contribution and justify each ranking. (7 marks)
4. The student's discussion claims "the experiment was very accurate." Identify three problems with this evaluation statement (in QCAA top-band evaluation style) and rewrite a one-paragraph evaluation that addresses each problem with specific reference to the IA2 student-experiment context of an acid-base titration of an unknown carboxylic acid. (6 marks)
5. A measured concentration of ethanoic acid in vinegar is reported as $1.02 \pm 0.04 \ \text{mol L}^{-1}$. The accepted value from the label is 1.00 mol L$^{-1}$. (a) Calculate the absolute and percentage error. (b) State whether the measurement is consistent with the accepted value, justifying with reference to the uncertainty interval. (c) Propose a controlled-variable improvement and a procedural improvement that together would reduce the dominant uncertainty source. (5 marks)
6. The student linearises $1/[A] = 1/[A]_0 + kt$ for a second-order reaction. Five data points $(t, 1/[A])$: (0, 1.00), (30, 1.42), (60, 1.85), (90, 2.30), (120, 2.71) in units of s and L mol$^{-1}$. (a) Calculate $k$ using a least-squares estimate based on the first and last points and report it with units. (b) Explain why min/max line method is preferred over single-point gradient for a top-band IA2. (c) Identify one source of systematic error in this kinetic measurement and propose a specific procedural modification. (6 marks)