Reproducible Chemical Testing

Overview

Students investigate a chemical sciences question using a practical investigation that avoids traditional bench-lab work (using safe, classroom-friendly “mini-tests” with structured procedures and controlled variables). The focus is on planning, running, and evaluating a valid, reproducible method, including hazard identification and risk control.

Learning intentions

WALT conduct a safe and reproducible scientific investigation to collect valid data in a chemical sciences context.

Success criteria

Students will be able to:

identify hazards, assess risks, and apply appropriate control measures before starting
follow a reproducible procedure (same steps, same settings, same measurement approach)
collect accurate, clearly recorded observations and data in an agreed format
evaluate possible sources of error and suggest improvements for further trials

Curriculum links

AC9S9I02 plan and conduct valid, reproducible investigations, including controlling sources of error, risk assessment, and considering ethical and heritage responsibilities as relevant
AC9S9I08 write and create texts to communicate ideas and findings, including discussing validity and reproducibility in a short report
AC9S1I02 (applied safety focus) suggest and follow safe procedures during investigations, with emphasis on hazard control and safe handling

Lesson structure (60 minutes)

0–5 min · Hook (scenario + question). Teacher shows a “mystery mixture” card: students must test which indicator change is most consistent (e.g., colour change intensity) when reacting with different household-safe solutions provided. Students choose a test question and write a one-sentence hypothesis.
5–12 min · Safety briefing + hazard hunt. Teacher introduces the investigation materials (teacher-managed): pH indicator strips or safe universal indicator solution, measured droplets, waste container, eye protection, gloves if required, and a simple timing tool. Students, in pairs, complete a quick hazard/risk/control checklist (eye splash, staining, slips, disposal) and confirm controls with the teacher.
12–22 min · Validity & reproducibility mini-teach. Teacher explains validity (the method tests the question) and reproducibility (another group can repeat and get similar results), then demonstrates how to keep variables controlled (same volume, same time window, same indicator type, same lighting/reading method). Students watch and then restate: “What must be identical for reproducibility?”
22–45 min · Investigation rounds (non-bench practical). Teacher assigns roles: Safety Officer (checks controls), Recorder (data sheet), Measurer (timing/volumes), Reader (indicator reading). Students run the procedure for at least two trials per group, recording data consistently (e.g., indicator colour category with numeric code, time to first change, and qualitative observations). Teacher circulates to support correct measurement, accurate recording, and safe practice.
45–52 min · Error check + evidence for validity. Students compare trial results within their group and identify at least two possible sources of error (e.g., inconsistent reading, timing differences, contamination between samples). They decide if additional variable control or an extra trial is needed to strengthen reproducibility.
52–59 min · Share-out + quick written conclusion. Students complete a short “micro-report” paragraph (3–5 sentences): what they tested, key result pattern, and a statement about validity/reproducibility plus one improvement. Each group shares one improvement.
59–60 min · Exit ticket. Students answer: “What control did you keep the same so your method is reproducible?” and “Name one risk and its control measure.”

Resources

Teacher-provided safe chemical testing kit (indicator strips/universal indicator, pre-labelled solutions, droppers or measured pipettes)
Eye protection, disposable gloves if required
Timer, tongs/lab scoop if needed, paper towels
Data recording sheets (table with trial 1/2, time window, indicator code, observations)
Hazard/risk/control checklist sheet
Waste disposal containers and class procedures signage
Coloured cards or a simple indicator reference key for consistent reading
Dyslexia-friendly sentence-starters and large-print procedure cards

Video Resources

Assessment

Formative: teacher observation of safety controls, correct measurement habits, and role responsibilities during trials
Formative: check recorded data for consistency, completeness, and clarity of observations
Summative (light): micro-report paragraph includes validity/reproducibility statement and at least one source of error with improvement; plus exit ticket

Differentiation

Scaffolded procedure: provide step-by-step cards with icons (start/measure/wait/observe/record) and a “same every time” checklist
Sentence starters for dyslexia-friendly writing: “We tested…”, “Our result showed…”, “Our method is reproducible because…”, “A possible error was…”
Reading support: colour-coded headings, short sentences, and reduced text on the procedure; teacher reads aloud the first time then students follow
Support for EAL: bilingual vocabulary prompt cards (e.g., hazard, risk, control, measure, trial, reproducible)
Structured recording: preset data table with predefined indicator code categories to reduce copying demands
Resilience routine: “Stop–Check–Restart” strategy if a measurement is missed (students repeat the step safely, not the whole task)

Extension (advanced learners)

Add a controlled variation test: compare two timings (e.g., 30 s vs 60 s) while keeping all else constant, and predict which timing better supports reproducible readings.
Quantify uncertainty: estimate how variable the indicator codes were across trials and propose a clearer reading standard (e.g., different lighting angle, second reader verification).
Method refinement: write an improved procedure for another class to replicate, including how to reduce the specific identified error.

Teaching Instructions