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Colour Change Investigation Worksheet

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Colour Change Investigation Worksheet

Finn, Levi and Aisha are checking water samples at a volcano observatory. They use red cabbage indicator to investigate whether familiar liquids are acidic, neutral or basic. Work through the evidence, then plan a fair test. Safety: wear eye protection, use small labelled samples, never taste chemicals, avoid skin contact, clean spills promptly and wash your hands. Follow adult instructions; do not test unknown liquids without supervision.

What happened?

The team added the same amount of indicator to equal volumes of each sample. They observed the colours below. Red cabbage indicator is usually purple; acids often turn it pink or red, while bases often turn it blue or green. These colour patterns are clues, not precise pH measurements.

Sample

Liquid

Colour after indicator

Lemon juice

Pink-red

Baking soda solution

Blue-green

Water

Purple

Vinegar

Pink-red

1.Which two tested liquids gave the strongest clue of being acidic? Use the observations to support your answer.

2.Classify sample B as acidic, neutral or basic, and state the evidence.

3.Why is water a useful comparison sample in this investigation?

4.A mystery liquid turns the indicator purple. What is the most careful conclusion?

It must be an acid.
It appears neutral, but the indicator result alone is not a precise measurement.
It must be a base.
It is definitely pure water.

Design a fair test

The team wants to compare how strongly different diluted samples affect the indicator. A fair test changes one factor at a time and keeps other conditions the same.

5.Identify the independent variable (what is deliberately changed) when comparing the different samples.

6.Name two variables the team should keep the same to make the comparison fair.

7.Put these method steps in a sensible order by writing the numbers 1–4 beside them: record the colour; add the same amount of indicator; label equal-volume samples; observe after the same wait time.

8.The team repeats each test three times and the colours match each time. How does repeating help?

9.True or false: A colour change by itself proves that a new substance has formed. Explain briefly.

10.Write a short evidence-based conclusion using the observations. Include one limitation of this test.