Module 5 Intro

1. Module 5 Intro

1.31. Page 2

Lesson 5

Module 5—Acids and Bases

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Try This

Red cabbage is another food that can change colour depending upon pH. Some of the compounds within the leaves of red cabbage are pH indicators. Follow the procedure below to investigate some of the colours that can be produced by the juice from red cabbage.

Problem

What effect do different substances have on the colour of red cabbage juice?

Procedure

Step 1: Place 2 cups of finely chopped red cabbage in a bowl.

Step 2: Pour boiling water into the bowl, using just enough to cover the red cabbage.

Step 3: After 20 minutes, drain the liquid from the bowl into a glass and set the cabbage aside.

Step 4: On a white plate, place three separate drops of red cabbage juice.

Step 5: Add one drop of lemon juice or vinegar to the first drop of red cabbage juice.

Step 6: Add one drop of water to the second drop of red cabbage juice.

Step 7: Add a pinch of baking soda to the third drop of red cabbage juice.

Observations and Analysis

TR 1. Record your observations in a suitable data table.

TR 2. Explain how the colour changes in red cabbage could not be explained as an effect of dilution of the red cabbage juice.

TR 3. Do you think that red cabbage juice could serve as a readily available substitute for litmus paper?

Check your work.

Try This Answers

TR 1. A sample data table is given.

Drop	Contents	Colour
1	red cabbage juice and lemon juice or vinegar	pink
2	red cabbage juice and water	purple
3	red cabbage juice and baking soda	blue-green

TR 2. The colour changes observed in drops 1 and 3 are distinctly different colours. A dilute pink colour does not appear blue-green.

TR 3. Red cabbage juice could be used as a replacement for litmus because there are distinctly different colours for an acidic solution and for a basic solution. It allows for a clear indication of the acidity or basicity of the solutions.