Year 8 Science · Unit 3 · Lesson 4
Challenge Worksheet
Learning Goals
Find the mistake
A student wrote this answer
"In our experiment, we mixed two clear solutions together and the mixture turned bright blue. I can clearly conclude that a chemical reaction has occurred because colour change is one of the five signs of a chemical reaction. The blue colour is proof that new substances have formed, so my investigation is complete and my conclusion is solid."
1. Identify the main scientific error in the student's conclusion. What has the student assumed that may not be true?
2. Describe a physical process that also causes a colour change (without a chemical reaction occurring). Use this as a counter-example to challenge the student's logic.
3. List at least three additional pieces of evidence the student should have collected to build a stronger conclusion. For each, explain what that evidence would show.
1. The Great Barrier Reef Marine Park Authority monitors chemical changes in water (e.g. ocean acidification) using multiple measurements. Name two measurable signs of a chemical change in ocean water and explain what each would indicate about the reef chemistry.
2. A student mixes two colourless liquids together. The only observation they make is that the solution turns yellow. A second student says this proves a chemical reaction occurred; a third says it doesn't. Whose reasoning is more scientifically sound, and what additional evidence would make either conclusion more certain?
Wrap Up
In one sentence, what was the main idea of this lesson?