What is QCE Chemistry IA2?

IA2 is the Student Experiment, the second internal assessment of Unit 3. Students design and conduct an experimental investigation, then write a scientific report (up to 10 pages including diagrams). Worth 20 percent of the subject result. Typically completed across Unit 3 plus early Unit 4.

Four assessment criteria from the QCAA Chemistry syllabus: Research and Planning, Analysis of Evidence, Interpretation and Evaluation, Communication. Each criterion has a marking grid with descriptors. Top band requires excellence on all four.

What is a good research question?

A specific, testable question that modifies or extends an existing chemistry investigation. Identifies an independent variable, dependent variable, and controlled variables. Example: 'How does the concentration of HCl (0.05 to 0.50 M) affect the initial rate of reaction with calcium carbonate at 25 degrees C?'

What kind of data analysis is expected?

Tabulated raw data plus processed data (means, uncertainties, derived quantities). Graphs with linear regression where appropriate, gradient and intercept reported with units. Uncertainty propagation. Identification of trends and quantitative relationships.

What are common errors in IA2?

Research question too broad or too narrow. Methodology under-controlled (too few controls). Insufficient replicates (5 minimum). Inadequate uncertainty analysis. Conclusion not linked back to the research question. Discussion limited to listing errors without analysing their impact.

QLDChemistry

QCE Chemistry IA2 Student Experiment: 2026 guide

A 2026 guide to QCE Chemistry IA2 (Student Experiment). The four marking criteria, research question construction, methodology and data analysis, common pitfalls, and a preparation timeline.

Generated by Claude Opus 4.815 min readQCAA-CHEM-IA2Updated 2026-06-20

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What IA2 is
Assessment criteria
Research question construction
Methodology
Data collection
Graphing and regression
Uncertainty analysis
Interpretation and evaluation
Communication
Common pitfalls
Timeline
Check your knowledge

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:

Research and Planning. Quality of the research question, hypothesis, methodology, identification of variables, justification of choices.
Analysis of Evidence. Quality of data collection, tabulation, processing, graphing, uncertainty.
Interpretation and Evaluation. Quality of analysis, conclusion, evaluation of methodology, limitations, suggestions for improvement.
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:

Apparatus and reagents with quantities and uncertainties (50 mL volumetric flask plus or minus 0.05 mL).
Procedure as numbered steps reproducible by another student.
Risk assessment (hazards, controls).
Identification and control of variables.
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.

Iron-tablet assay setup: standardised

\text{KMnO}_4

dripped from a burette into acidified

\text{Fe}^{2+}

solution; endpoint is the first faint persistent pink, reproducible to within

\pm 0.05

mL.

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.

AAS calibration curve: five standards bracketing the unknown sit on a straight line through the origin; the unknown's absorbance projects horizontally to the line then vertically to read the concentration as 4.7 ppm.

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.

Error-source ranking for the iron-tablet titration: end-point detection (random) and glassware tolerance (systematic) dominate; QCAA "interpretation and evaluation" rewards naming both type and magnitude per source.

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.

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)
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)
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)
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)
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)
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)

Solutions

Q1: Refined: "What is the relationship between temperature (15.0, 25.0, 35.0, 45.0, 55.0 degrees C, $\pm 0.2$ degrees C) and the initial rate of reaction between $0.100 \ \text{mol L}^{-1}$ HCl and $0.020 \ \text{mol L}^{-1}$ sodium thiosulfate, measured as time to cross-occlusion ( $\pm 0.2 \ \text{s}$ )?" Justifications: (i) named chemical context (thiosulfate-acid sulfur precipitation) tied to one Unit 3 collision-theory equation, not a generic "rate of reaction"; (ii) the IV is five distinct controlled values spanning a meaningful range with stated precision; (iii) the DV is measurable to under 5 percent precision with a school stopwatch and stated detection method; (iv) units and precision are explicit throughout. This question rewards application of the IA2 research-question criterion (application and knowledge and analysis criteria together).
The refined question names context, sets five precise IV values, defines a measurable DV with precision, and ties to one Unit 3 equation.
Q2: Five controlled variables: (1) Temperature - $K_c$ varies with temperature so all trials must be at the same thermostatted temperature (typically 25.0 $\pm$ 0.2 degrees C) measured before each reading. (2) Water-ethanol ratio - solvent polarity shifts the equilibrium position; varying the cosolvent fraction would confound $[Cl^-]$ effects. (3) Total volume of solution - the cuvette pathlength is fixed but the absorbance is proportional to concentration; volume changes would dilute species. (4) Cuvette identity and pathlength - small variations in cuvette glass produce baseline absorbance shifts that bias the colorimetric reading. (5) Wavelength of measurement - 690 nm is near the $[CoCl_4]^{2-}$ peak; drifting away from peak changes molar absorptivity. This question tests knowledge of equilibrium and application to colorimetric measurement (knowledge and analysis, application criteria).
Five controlled variables: temperature, water-ethanol ratio, total volume, cuvette identity, and wavelength.
Q3: (a) For a reaction first-order in $[KI]$ , rate $\propto [KI]$ , so the plot of initial rate versus $[KI]$ is linear through the origin. (b) Gradient using first and last points: $(8.45 - 0.84)/(0.100 - 0.010) = 7.61/0.090 = 84.6 \ \text{mL O}_2 \ \text{s}^{-1} \ (\text{mol L}^{-1})^{-1}$ . (Each intermediate point lies within 3 percent of the line, supporting first-order kinetics.) (c) Largest: gas-volume read-off uncertainty in the first 5 seconds when bubbles are still equilibrating in the delivery tube ( $\pm 0.5$ mL on volumes of 4 to 8 mL is about 10 percent). Medium: $[KI]$ pipetting uncertainty ( $\pm 0.05$ mL on 5.00 mL is 1 percent). Smallest: temperature fluctuation over the 10-second initial-rate window ( $\pm 0.3$ degrees C contributes under 0.5 percent via the rate-temperature relationship for this reaction). Justification of ranking: the first dominates because initial-rate methods amplify early-time noise; later sources scale linearly with concentration or temperature. This question rewards application of rate law, knowledge of error sources, and judgement of ranking (judgement criterion).
Rate is first-order in $[KI]$ with rate constant $84.6 \ \text{mL O}_2 \ \text{s}^{-1} \ (\text{mol L}^{-1})^{-1}$ ; early-time gas-volume read-off dominates the uncertainty budget.
Q4: Three problems: (1) "Very accurate" is vague: QCAA top-band requires quantified percentage error and reference to specific uncertainty sources, not adjectival claims. (2) The statement conflates accuracy (closeness to true value) with precision (spread of repeats) without distinguishing; both must be evaluated separately. (3) The statement lacks justification: no modification proposal follows, leaving the discussion criterion only half complete. Rewrite: "The mean measured pKa of the unknown carboxylic acid was 4.78 $\pm$ 0.06, agreeing with the literature value for propanoic acid (4.87) to within 1.9 percent and within the propagated uncertainty range. Precision (RSD 1.2 percent across five replicates) was limited by visual endpoint determination of phenolphthalein, the dominant random source; accuracy was likely affected by trace dissolved $CO_2$ depressing the apparent pKa by under 0.05 units, a systematic source. To address both: a calibrated pH probe replacing visual indicator would reduce random uncertainty by an estimated factor of three; deaerating with $N_2$ for 5 minutes before titration would address the $CO_2$ systematic shift." This question tests judgement (judgement criterion) and communication of structured evaluation (communication criterion).
A top-band evaluation quantifies error, separates accuracy from precision, names specific sources, and proposes targeted modifications.
Q5: (a) Absolute error $= |1.02 - 1.00| = 0.02 \ \text{mol L}^{-1}$ . Percentage error $= 0.02/1.00 \times 100 = 2.0 \ \text{percent}$ . (b) The uncertainty interval $1.02 \pm 0.04$ spans 0.98 to 1.06 mol L $^{-1}$ , which contains the accepted 1.00; the measurement is consistent with the accepted value. (c) Controlled-variable improvement: temperature-control titration in a water bath at 25.0 $\pm$ 0.2 degrees C (the titre depends slightly on temperature through indicator pKa drift). Procedural improvement: replace visual phenolphthalein with calibrated pH-probe inflection-point detection, which directly addresses the dominant random source (endpoint identification). Combined, these reduce the relative uncertainty from 4 percent to approximately 1 percent. This question tests application of error analysis (application criterion) and judgement of improvement (judgement criterion).
The 2 percent error is within the 4 percent stated uncertainty; pH-probe endpoint plus thermostatting are the targeted improvements.
Q6: (a) Gradient $= (2.71 - 1.00)/(120 - 0) = 1.71/120 = 0.01425 \approx 1.43 \times 10^{-2} \ \text{L mol}^{-1} \ \text{s}^{-1}$ . This is $k$ for a second-order rate law. (b) The min/max line method bounds the gradient using the steepest and shallowest lines that pass through every error bar, yielding an uncertainty in $k$ directly; single-point gradient ignores intermediate points and discards information about scatter, so the calculated $k$ has no associated uncertainty for the discussion. QCAA top-band evaluation requires a quantified uncertainty in the gradient, which the min/max method provides graphically and the linear-regression method provides numerically. (c) Systematic source: temperature drift over the 120-second measurement window changes $k$ exponentially (Arrhenius); a 5 degrees C drift typical of a room-temperature reaction would shift $k$ by around 50 percent. Modification: thermostat the reaction vessel in a water bath set to 25.0 $\pm$ 0.2 degrees C, monitor temperature with a thermistor logging at 1 Hz, and discard any trial where temperature drifts above $\pm 0.5$ degrees C. This question rewards application of linearisation and rate law (application criterion), judgement of gradient methods (judgement criterion), and communication of a specific improvement (communication criterion).
$k = 1.43 \times 10^{-2} \ \text{L mol}^{-1} \ \text{s}^{-1}$ ; min/max gradient gives quantified uncertainty; thermostatting addresses the dominant systematic.