Red rose as an indicator

No litmus at home? Flowers can do the job. Activity 2.3 makes an indicator from red roses.

• Collect fallen red rose petals. Do not pluck flowers.
• Wash a fistful and crush them with a mortar and pestle.
• Put them in a glass tumbler and pour in hot water till the petals are covered. Do this step with an adult.
• Cover it and wait 5 to 10 minutes till the water turns coloured.
• Filter it. The liquid that comes through, the filtrate, is your indicator.

In Activity 2.4 you add lemon juice to one tube of extract (A) and soap solution to another (B). Red rose extract turns red in an acid and green in a base. In a neutral substance it does not change.

Compare with litmus: the things that turned the rose extract red are the same ones that turned blue litmus red. So the rose extract is another acid-base indicator.

You can make indicators the same way from beetroot, purple cabbage, turmeric, jamun (Indian blackberry) and red hibiscus (gudhal).

A flower that tests its own soil. The hydrangea grows in the cool Himalayan region and the North-east. In acidic soil its flowers come out blue; in basic soil they are pink or red. So a gardener can change the flower colour by changing the soil.