Practical Planning Focus

Overview

Students will design a fair practical investigation to test how temperature affects the rate of reaction using sodium thiosulfate and hydrochloric acid. They will practise selecting variables, writing a method, and planning how they will collect reliable data and use it to justify conclusions.

Learning intentions

• Students will plan a fair test investigating the effect of temperature on reaction rate using sodium thiosulfate and hydrochloric acid.
• Students will identify the independent, dependent, and controlled variables and choose suitable measurements for rate.
• Students will write a clear method that links observations/data to the chemical reaction context.
• Students will anticipate risks and plan safe working procedures.

Success criteria

• I can state the investigation question and predict the likely trend when temperature changes.
• I can list the independent, dependent, and controlled variables and explain why they are controlled.
• I can plan a method that produces repeatable results and includes a results table.
• I can describe how I will measure reaction rate consistently (e.g., time to a fixed observation).

Curriculum links

• AS91921: Demonstrate understanding of scientific investigative approaches in a context (focus on describing the purpose and evidence for approach choices).
• AS92021: Demonstrate understanding of chemical reactions in context (focus on linking the reaction to context and conserving mass via equations as part of interpreting results).
• Key science skills: fair testing, recording data, using observations, and evaluating reliability of evidence.

Lesson structure (60 minutes)

1. 0–5 min · Hook and context prompt. Teacher shows a real-life style scenario slide with: “Why do hot showers feel faster to clean than cold ones?” (linking to faster reactions at higher temperature) and asks students what would happen if two identical “reaction mixtures” were at different temperatures. Students quick-write one idea and one question they now have about testing it.

2. 5–12 min · Set up the reaction and rate idea. Teacher leads a short explanation: sodium thiosulfate reacting with hydrochloric acid produces sulphur (cloudiness) and new substances; students recall that reaction rate can be tracked by time taken to reach a fixed observable endpoint (e.g., visible cloud/tick mark). Students complete a brief “rate measurement” check: choose one measurable endpoint and state why it is consistent.

3. 12–22 min · Direct teach: fair test planning. Teacher models a planning checklist on the practical planning deck: independent variable (temperature), dependent variable (time to endpoint), controlled variables (volumes/concentrations/mass if used, container type, mixing start/stop rule, stirring technique, same endpoint definition). Students annotate the model and add missing controls.

4. 22–34 min · Method design in pairs. Teacher circulates while students use the planned variables to draft a full method: prepare thiosulfate at set temperatures, add acid to start the reaction, start timing at the exact moment of mixing, record time at the same endpoint, repeat for reliability (at least 3 trials per temperature). Students draft a method and results table headings (Temperature, Trial 1–3, Mean time).

5. 34–42 min · Safety and investigation approach. Teacher prompts students to add risk & safety steps (eye protection, handling acids, spill response, disposal, safe heat sources if using warm baths). Students update their plans with a short safety section and one sentence explaining why their approach is appropriate to answer the question (linked to investigative approach purpose).

6. 42–50 min · Share-out: reliability and consistency checks. Teacher runs a quick “gallery” discussion using the practical planning deck: students compare at least two plans and discuss: “What would make results unreliable?” and “What change would improve fairness?” Students choose one improvement they will make and justify it.

7. 50–58 min · Whole-class synthesis to AS91921/AS92021. Teacher connects planning to evidence and interpretation: students must be able to explain how their method will produce evidence to show the pattern/trend, and how the reaction is the same chemical process each time (same reactants, balanced equation conceptually; interpreting conserved mass in discussion later). Students complete a 3-sentence “link” statement: (1) reaction type/context, (2) variables, (3) evidence and endpoint.

8. 58–60 min · Exit slip. Teacher collects a short exit response from each student: “My independent variable is… My endpoint is… I will repeat… because…”

Resources

• the practical planning deck
• the practical planning worksheet
• Sodium thiosulfate solution, hydrochloric acid (for teacher demonstration samples or context only)
• Thermometer / temperature probe access for planning reference
• Safety eyewear and gloves for classroom safety talk
• Heat source options (e.g., warm water bath) shown as apparatus photos/pointers (no full setup required for planning)
• Data table print on the practical planning worksheet
• Markers/pen, highlighters for variable identification
• Pair planning space and rough scrap paper

Assessment

• Formative checks during pair work: teacher observes whether students correctly identify variables and define a consistent rate endpoint.
• Method review: teacher checks for clear start/stop timing rule and repeat trials.
• Exit slip: verifies students can state independent/dependent/controlled variables and the evidence plan.

Differentiation

• Support for students who need scaffolding:
• Sentence starters on the practical planning worksheet (e.g., “I will measure rate by… because…”, “To keep it fair, I will…”) and a model endpoint definition.
• Provide a variable bank (Temperature, Time to endpoint, Same volume, Same concentration, Same container, Same stirring method) for students to choose from.
• For students needing reduced reading load:
• Dyslexia-friendly option: teacher reads aloud the planning instructions; students use high-contrast highlighting to find key terms (independent/dependent/controlled).
• Extension for advanced students:
• Add a “What if?” reliability check: propose how you would handle outliers (e.g., one trial clearly inconsistent) and how that affects the mean.
• Plan a second dependent-variable option (e.g., distance of thiosulfate cloud boundary at a fixed time) and justify which is better for interpreting rate.
• EAL considerations:
• Encourage visual mapping (arrow diagram: temperature → rate/time) and model the use of connectives: “because”, “so that”, “therefore”.

Extension (optional)

• None.