QCE Chemistry IA2 student experiment template: The 2026 guide

Study guide16 min readUpdated 21 May 2026

Quick answer

The QCE Chemistry IA2 student experiment is a 2000-word scientific report on a student-designed Unit 3 investigation (common contexts: equilibrium effects, acid-base titrations, galvanic cells); top-band reports demonstrate a specific testable research question, systematic uncertainty handling (random and systematic, propagated through calculations), linearisation where applicable, gradient extraction with min/max line method, and a discussion that names uncertainty sources tied to specific experimental steps with suggested improvements.

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What this guide is for
Marking criteria
Scientific report structure
Three common contexts
Research question
Uncertainty handling
Linearisation and gradient
Discussion
Check your knowledge

What this guide is for

The QCE Chemistry IA2 student experiment is a major assessment. This guide covers the scientific report structure, marking criteria, common contexts, and the writing moves that distinguish top-band from middle-band reports.

Marking criteria

QCAA publishes detailed marking criteria. The major categories:

Research and planning. Quality of research question, hypothesis, methodology.
Analysis of evidence. Data analysis, uncertainty, graphical representation.
Interpretation and evaluation. Discussion of results, uncertainty sources, limitations.
Conclusion. Direct answer to the research question.

Top band requires excellence in all four.

Scientific report structure

Title: Specific and descriptive.
Abstract: Around 150 words. The question, methodology, key result, conclusion.
Introduction

Research question (specific, testable).
Theoretical framework (relevant Unit 3 theory).
Hypothesis (with prediction).
Aim.

Method.

Variables (independent, dependent, controlled).
Apparatus (labelled diagram).
Procedure (step-by-step, detailed).
Risk assessment.

Results.

Raw data table with units and uncertainties.
Processed data table with units and propagated uncertainties.
Graph(s) with uncertainty bars.

Analysis.

Calculations (with uncertainties).
Best-fit line; gradient and intercept with uncertainty.
Comparison to theoretical predictions.

Discussion.

Uncertainty sources (random and systematic).
Limitations of the investigation.
Suggested improvements.
Implications.

Conclusion. Direct answer to research question with experimental result and uncertainty.

References.

A top-band IA2 connects hypothesis to graph: each stage matches a specific ISMG criterion and the visual workflow makes the chain explicit for the marker.

Hypothesis-to-graph workflow with ISMG tags: every step has an evidence trail that the marker can pin to a single criterion, and the conclusion loops back to answer the original research question.

A controlled-variable matrix lists every variable, declares it independent, dependent or controlled, and names the method of control. QCAA "research and planning" wants the matrix visible, not buried in prose.

Controlled-variable matrix for the iron(III) thiocyanate IA2: one independent, one dependent, six controlled with named methods of control; the table makes the ISMG "research and planning" tick boxes visible at a glance.

Three common contexts

Equilibrium (Topic 1)

Investigate the effect of concentration or temperature on the position of equilibrium for a specified reaction.

Common system: iron(III) thiocyanate.

$\text{Fe}^{3+} + \text{SCN}^- \rightleftharpoons \text{FeSCN}^{2+}$
The complex is deep red; allows colorimetric monitoring. Add Fe $^{3+}$ or SCN $^-$ to shift equilibrium; observe colour change.

Titration (Topic 1)

Determine the concentration of an acid or base in a sample using standardised reagent.

Common: vinegar (ethanoic acid). Titrate with standardised NaOH. Use phenolphthalein indicator. The mass percentage of ethanoic acid in commercial vinegar is around 5%.

Galvanic cell (Topic 2)

Construct a galvanic cell and measure its potential; compare to the theoretical value from standard reduction potentials.

Common: Zn/Cu cell. Theoretical $E^0_{cell} = +1.10$ V. Compare measured potential to theoretical; account for any deviation.

Research question

Must be specific. Example weak: "How does temperature affect the iron(III) thiocyanate equilibrium?"

Example strong: "How does temperature (in the range 10 to 60 degrees C in 10-degree intervals, with a tolerance of plus/minus 0.5 degrees C) affect the equilibrium concentration of FeSCN $^{2+}$ (measured via UV-visible absorbance) in a system with initial concentrations of 0.10 M Fe(NO3)3 and 0.10 M KSCN?"

The strong version specifies ranges, increments, tolerances, and measurement methods.

Uncertainty handling

Random uncertainty: From repeated measurements (typically 3-5 trials). Estimate by half-range or standard deviation.
Systematic uncertainty: From instrument bias (zero offset, calibration). Estimate from instrument specifications.
Instrumental uncertainty: Half the precision (typically).
Propagation

Addition/subtraction: add absolute uncertainties.
Multiplication/division: add fractional uncertainties.
Powers: multiply fractional uncertainty by the power.

Reporting. Value plus/minus uncertainty, consistent decimal places.

Linearisation and gradient

For a non-linear relationship, linearise before plotting.

Example. For a titration to determine Ka, plot pH vs log([A $^-$ ]/[HA]); the intercept is pKa.

Gradient uncertainty: max-slope line and min-slope line through error bars; half-range of the two slopes is the gradient uncertainty.

A percent-error plot compares the measured result for each trial against the accepted value and visualises both accuracy (closeness to the accepted line) and precision (scatter between trials).

Percent-error plot for the Zn-Cu galvanic cell IA2: all five trials sit inside the

\pm 5\%

band against the accepted

E^\circ_{\text{cell}} = +1.10

V, with mean error

+1.2\%

; accuracy and precision read off one figure.

Discussion

Strong discussions:

Uncertainty sources: Name specific sources tied to specific experimental steps. Random (variation in burette readings) vs systematic (calibration error). Major contribution vs minor.
Limitations: What the investigation cannot conclude. Are controlled variables truly held constant? Is the range of the IV sufficient? Are the trials enough?
Improvements: Specific changes that would reduce uncertainty or extend the result. Use longer pendulum; use more trials; use better instrument.

Common errors

Research question too broad: Specify ranges and tolerances.
Insufficient data points: Use at least 5 across the IV range, with 3-5 trials per point.
No uncertainty propagation: Every numerical result should have uncertainty.
Limitations as decoration: Each limitation must be argued; "human error" without specificity is meaningless.
Conclusion without answer: Always state the experimental result and compare to expectations explicitly.

Check your knowledge

Six questions covering the full IA2 student-experiment workflow: hypothesis to research question, methodology design, data processing, evaluation, and modification. ISMG criteria are signposted in the solutions. Three significant figures and units throughout.

State the difference between a hypothesis and a research question in IA2 terms, then convert the hypothesis "Increasing concentration of acid increases the rate of reaction with magnesium" into a research question that meets QCAA top-band specificity. (3 marks)
A galvanic-cell study measures cell potential $E_{cell}$ for $Zn / Zn^{2+} \| Cu^{2+} / Cu$ at five $[Cu^{2+}]$ values (0.010, 0.050, 0.100, 0.500, 1.00 mol L $^{-1}$ ) at constant $[Zn^{2+}] = 1.00 \ \text{mol L}^{-1}$ and 25.0 degrees C. Observed potentials (V): 1.044, 1.064, 1.073, 1.091, 1.100. (a) Use the Nernst equation $E = E^{\circ} - (0.0592/n) \log([Zn^{2+}]/[Cu^{2+}])$ to predict $E_{cell}$ at $[Cu^{2+}] = 0.100$ mol L $^{-1}$ given $E^{\circ}_{cell} = +1.10$ V. (b) Compare prediction with observation and state a claim with justification. (c) Identify the dominant source of uncertainty and propose a procedural modification. (7 marks)
The student's data shows that an unknown weak acid has $pK_a = 5.13$ with relative standard deviation 0.8 percent across five replicates. Literature values: ethanoic acid $pK_a = 4.76$ , propanoic acid 4.87, butanoic acid 4.82, benzoic acid 4.20, salicylic acid 2.97. (a) State which acid is the most likely identity, justifying with reference to RSD and the gap to other literature values. (b) Identify a controlled-variable issue that might shift the measured $pK_a$ from the true value of the candidate acid. (c) Propose a confirmation procedure (independent measurement) to test the identification. (5 marks)
A titration uses a 25.00 mL pipette ( $\pm 0.04$ mL), a 50.00 mL burette ( $\pm 0.05$ mL each reading), and a 0.1000 mol L $^{-1}$ ( $\pm 0.0002$ mol L $^{-1}$ ) NaOH standard. Mean titre 21.45 mL. (a) Calculate the percentage uncertainty in moles NaOH per titre. (b) Calculate the percentage uncertainty in the moles of acid in the 25.00 mL aliquot. (c) State which component contributes most to the combined uncertainty and propose one realistic modification to reduce it. (6 marks)
A research question reads "How does temperature (10, 20, 30, 40, 50, 60 degrees C, $\pm 0.5$ degrees C) affect the equilibrium constant $K_c$ for the reaction $2NO_{2(g)} \rightleftharpoons N_2O_{4(g)}$ in a sealed glass syringe?" Identify two practical or safety constraints with this question, and propose specific modifications to the methodology to address each. (4 marks)
The IA2 evaluation reads: "Two trials disagreed by 8 percent; this is likely random error so the experiment is precise." Identify three weaknesses in this evaluation and rewrite a one-paragraph QCAA top-band evaluation in the same context (acid-base titration, unknown weak acid identification). (5 marks)

Solutions

Q1: A hypothesis states a predicted relationship between variables; a research question asks what relationship will be investigated, with all measurable variables specified to QCAA precision. Converted: "What is the relationship between the concentration of hydrochloric acid (0.10, 0.25, 0.50, 0.75, 1.00 mol L $^{-1}$ , $\pm$ 0.005 mol L $^{-1}$ ) and the initial rate of reaction with excess magnesium ribbon (5.0 cm, fine sandpapered before each trial), measured as the volume of hydrogen gas evolved in the first 30.0 $\pm$ 0.2 seconds at 25.0 $\pm$ 0.5 degrees C?" This question tests knowledge of IA2 research-question conventions (knowledge and analysis criterion).
The IA2-style question names IV range and precision, controls magnesium surface area, defines the DV window precisely, and states temperature.
Q2: (a) $E = +1.10 - (0.0592/2) \log(1.00/0.100) = 1.10 - 0.0296 \times 1 = +1.070$ V. (b) Observed $E_{cell}$ at 0.100 mol L $^{-1}$ is 1.073 V; predicted 1.070 V; difference 0.003 V is within the typical voltmeter uncertainty (under $\pm$ 0.005 V), so the data are consistent with the Nernst equation and the claim "Nernst behaviour is observed across two decades of $[Cu^{2+}]$ " is supported. The full data set when plotted as $E$ versus $\log[Cu^{2+}]$ should give gradient $+0.0296$ V/decade. (c) Dominant uncertainty: salt-bridge liquid-junction potential drift over the measurement series, which adds a slowly varying offset to every reading. Modification: replace the agar salt bridge with a freshly prepared bridge for each $[Cu^{2+}]$ value, and record open-circuit potential for 60 seconds and take the asymptotic reading; alternatively use a reference electrode (Ag/AgCl) for absolute calibration. This question rewards application of Nernst (application criterion), judgement of agreement (judgement criterion), and communication of modification (communication criterion).
Prediction 1.070 V agrees with observation 1.073 V; salt-bridge junction potential is the dominant uncertainty with fresh-bridge replacement as the targeted modification.
Q3: (a) Most likely: propanoic acid (literature 4.87), since the measured $pK_a$ is 5.13 with RSD 0.8 percent (giving an interval roughly 5.09 to 5.17, lying 0.22 to 0.26 units above propanoic). The gap to butanoic (4.82) is similar; both are plausible. The next nearest candidate, ethanoic at 4.76, is well outside the RSD interval. Identification: propanoic or butanoic, leaning propanoic because of a slightly closer match to the typical positive shift caused by air- $CO_2$ uptake. (b) Controlled variable: trace $CO_2$ from air dissolves into the buffer-region solutions during the half-equivalence measurement, slightly raising $[H^+]$ and shifting the apparent $pK_a$ upward by around 0.1 to 0.2 units; this is consistent with the 0.26-unit gap to propanoic. (c) Confirmation: measure the molar mass independently by Schotten-Baumann derivatisation followed by spectroscopy, or by direct equivalence-point mass-titration (n = $C_{NaOH} V_{eq}$ giving moles; mass of acid known, so $M_r$ = mass/moles); $M_r$ of propanoic acid is 74.08 versus butanoic 88.11. This question tests application of pKa data (application criterion) and judgement against literature (judgement criterion).
Propanoic acid is the most likely identity given the air- $CO_2$ pKa shift; mass-titration $M_r$ determination is the confirmation procedure.
Q4: (a) Components: $V_{NaOH} = 21.45 \pm 0.05$ mL (one read at endpoint, since the burette is zeroed; for two-point read add $\pm 0.05$ in quadrature giving 0.071 mL but commonly $\pm 0.05$ mL is used for the meniscus difference). $C_{NaOH} = 0.1000 \pm 0.0002$ mol L $^{-1}$ . Percentage uncertainties: $V_{NaOH}$ : 0.05/21.45 = 0.23 percent; $C_{NaOH}$ : 0.0002/0.1000 = 0.20 percent. Combined for $n_{NaOH} = CV$ : $\sqrt{0.23^2 + 0.20^2} = 0.31$ percent. (b) Add aliquot uncertainty: $V_{aliquot} = 25.00 \pm 0.04$ mL, percentage 0.04/25.00 = 0.16 percent. Combined moles of acid (1:1 stoichiometry): $\sqrt{0.31^2 + 0.16^2} = 0.35$ percent. (c) Largest contributor: burette read at endpoint (0.23 percent) and standard concentration (0.20 percent) are comparable; the modification with highest impact is using a digital titrator or a 50 mL piston burette ( $\pm 0.01$ mL per read), reducing the burette uncertainty from 0.23 percent to 0.05 percent. This question rewards application of uncertainty propagation (application and knowledge and analysis criteria).
Combined uncertainty in acid moles is 0.35 percent; burette read-off is the dominant source with digital titrator as the modification.
Q5: Constraint 1 (practical): glass syringes leak gas at temperatures above ambient ( $\geq$ 40 degrees C); the equilibrium $2NO_2 \rightleftharpoons N_2O_4$ involves a 2:1 mole ratio, so any leak biases the measured $K_c$ downward as temperature rises. Modification: replace the glass syringe with a sealed gas-tight cell with septum-fitted sampling at each temperature, or use a sealed quartz cuvette monitored colorimetrically (NO $_2$ is brown; $N_2O_4$ is colourless). Constraint 2 (safety): $NO_2$ is highly toxic by inhalation; school laboratory ventilation may not permit work at elevated temperature with a leaking system. Modification: conduct the experiment in a fume hood with continuous flow, use a sealed cuvette to avoid release entirely, and consider an alternative equilibrium (the $Co(H_2O)_6^{2+}/CoCl_4^{2-}$ colour change) that demonstrates the same chemistry without toxic gas. This question rewards judgement of practical and safety constraints (judgement criterion) and communication of modifications (communication criterion).
Gas leak above ambient and $NO_2$ toxicity are the two constraints; sealed cuvette colorimetry in a fume hood addresses both.
Q6: Weaknesses: (1) 8 percent disagreement between trials with only two trials cannot be classified as random without more replicates; minimum five trials are needed to estimate RSD. (2) "Precise" is misapplied: an 8 percent spread is poor precision (typical IA2 RSD for titration is under 1 percent). (3) No source-attribution of the variation, no quantified uncertainty, and no proposed modification. Rewrite: "The two trials yielded $pK_a$ values of 4.62 and 5.02, an 8 percent spread (RSD over the two replicates alone is 5.5 percent). This is well above the 1 to 2 percent RSD expected for a titration-derived $pK_a$ and indicates a procedural defect rather than random scatter. The dominant likely source is inconsistent identification of the half-equivalence-point pH from a visual indicator transition; phenolphthalein is unreliable in the pH 4.5 to 5.0 buffer region of a weak acid. Two further replicates with a calibrated pH probe yielded 4.83 and 4.85 (RSD 0.4 percent), supporting the procedural rather than random interpretation, and identifying the acid (within RSD interval of literature 4.87) as propanoic acid. The recommended modification for any future repeat is to use a pH probe throughout, eliminating indicator-judgement bias." This question tests judgement (judgement criterion) and communication of evaluation (communication criterion).
The original evaluation conflates precision with accuracy and lacks replication, source-attribution, and modification; the rewrite addresses all three with quantified data.

Sources & how we know this

Chemistry General senior syllabus 2025 — QCAA