Year 8 Science · Unit 3 · Lesson 11
Challenge Worksheet
Learning Goals
What if…?
Scenario
Two Year 8 students are both investigating the same question: "Does temperature affect the rate of the reaction between bicarbonate of soda and vinegar?" They use the same equipment and the same controlled variables. However, Student A conducts only 1 repeat trial at each temperature, while Student B conducts 5 repeat trials at each temperature. Both students get broadly similar results and write their conclusions.
(a) Predict how the reliability of their results would differ. Use the word "reliability" and explain your reasoning clearly.
(b) Would the validity of their investigations be the same or different? Explain why, referring to their experimental setup.
(c) Whose conclusion would a scientist have more confidence in? Explain why, and identify one additional factor (beyond repeat trials) that could further strengthen the investigation.
1. A student claims: "My experiment is reliable because I used the same equipment every time." Is this claim correct? Explain what reliability actually requires and whether their reasoning is sufficient.
2. Explain how a confounding variable can undermine the validity of an investigation even if the experiment is performed reliably with many repeat trials.
Wrap Up
In one sentence, what was the main idea of this lesson?