Year 10 Science · Unit 2 · Lesson 3
Challenge Worksheet
Learning Goals
Design a test
A scientist wants to investigate: "How can red cabbage juice be calibrated as a reliable pH indicator for classroom use?" Plan the investigation below.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables, list 3) | |
| What I will measure / observe (dependent variable) | |
| Materials needed (list at least 6 specific items) | |
| Step-by-step procedure (brief, 4 key steps) | |
| How I would create the colour reference chart | |
| One limitation of using red cabbage juice compared to a commercial pH meter |
1. A student calibrates their red cabbage indicator using solutions of pH 2, 4, 7, 10, and 12. They then test an unknown solution and get a blue colour. Using the calibration data, determine the approximate pH of the unknown solution and state whether it is acidic, neutral, or basic.
2. The colour of red cabbage juice can be bleached by strong oxidising agents such as chlorine bleach (sodium hypochlorite). Explain how this chemical property of bleach could lead to a misleading result when testing its pH with red cabbage juice. What alternative indicator would you recommend for bleach, and why?
3. Describe how you would present your colour reference chart so that another student could use it reliably to determine the pH of an unknown solution. Include what information the chart should display and how you would minimise subjectivity in colour matching.
Wrap Up
In one sentence, what was the main idea of this lesson?