Year 10 Science · Unit 2 · Lesson 19
Apply Worksheet
Learning Goals
Find the flaw
Read this student's CER conclusion from a thiosulfate clock reaction investigation. Three weaknesses have been hidden in the argument. For each weakness identified below, explain what is wrong and why it weakens the argument.
Student's CER conclusion
"Claim: Temperature affects reaction rate. Evidence: The reaction was faster at high temperatures than at low temperatures. Reasoning: When temperature goes up, the particles move faster and so they collide more often, making the reaction faster."
Weakness 1: The claim is too vague, it does not state the direction or size of the effect. Rewrite the claim with specific values from the thiosulfate data (20°C = 95 s; 60°C = 11 s).
Weakness 2: The evidence uses no numbers. Rewrite the evidence using at least two specific data values and include the calculated rate (1/time).
Weakness 3: The reasoning mentions collision frequency but ignores activation energy. Extend the reasoning to include why not just more collisions, but collisions exceeding the activation energy, matter.
Investigation question
"Does temperature affect the rate of the sodium thiosulfate clock reaction?" Data: at 20°C, the reaction took 95 seconds; at 30°C it took 52 seconds; at 40°C, 29 seconds; at 50°C, 17 seconds; at 60°C, 11 seconds. Use these data values and collision theory to write a full CER conclusion using the scaffold below.
Claim: State specifically what the data shows about the relationship between temperature and reaction rate.
Evidence: Quote at least two specific data values (time or calculated rate) to support your claim.
Reasoning: Use collision theory (particle kinetic energy, collision frequency, activation energy) to explain why the data shows this trend.
Wrap Up
In one sentence, explain why a CER conclusion that does not include specific data values is weaker than one that does.