Red cabbage pH indicator

Red Cabbage Does Stuff

What you will need for this experiment:

• 1 red cabbage
• grater
• 2 bowls or a saucepan
• jug
• strainer
• paper towels/coffee filters
• sheet of plain paper
• coloured pencils
• lemon juice
• orange juice
• vinegar
• milk
• tap water
• soapy water
• yoghurt
• 8 paper cups

What To Do:

1. Grate 1/2 the cabbage into a bowl. Fill the bowl with water and let it sit for a couple of hours. Drain the cabbage water into the other bowl. OR. Put the grated cabbage into the saucepan with enough water to just cover it. Boil for 20-30 minutes until the liquid turns a dark purple colour.
2. Let the cabbage juice cool and then strain into the jug.
3. Cut 2 inch (5 cm) strips out of the paper towels/coffee filters.
4. Soak the strips of paper in the cabbage juice until they turn bluish-purple.
5. Lay the strips flat on the bench/table and leave them to dry. These are your indicator strips.
6. Put the other liquids (lemon juice etc.) into separate cups.
7. Dip the indicator strips into one liquid each.
8. Using pencils and your plain paper, copy the colour that each strip turns.
9. Draw a picture, or write the name of the liquid that made the paper turn that colour.
10. Use your notes to make a chart showing the different colours that the liquids produced.

What Happens:

Your red cabbage juice is a simple pH tester. It reacts differently to different substances. Once you know what colour the juice turns in acids and alkalis, you can use it to test other liquids.

Why It Happens:

Red cabbage has pigments which react differently to acids and alkalis. When you dip the strips into a substance and wait for a few minutes, the colour will fully develop. The indicator strips turn red-yellow in acid, green in neutral and purple-blue in alkali.