NCERT Solutions for Class 7th Science Chapter 2 Activity 2.3: Let us prepare — Red rose as an indicator
Book page 12 Updated on2026-09-19
Q1.
Take a fistful of the collected petals of red roses and wash them with water. Crush the petals using a mortar and pestle. Place them in a glass tumbler. Pour some hot water into the glass tumbler to ensure that the crushed flower petals are completely immersed. Cover the glass tumbler with a lid. Wait for 5 – 10 minutes till the water becomes coloured (Fig. 2.6), and filter it. Prepare the red rose extract.
Fig. 2.6, page 12 — redrawn sketch. Crushed red rose petals immersed in hot water in a covered glass tumbler; after 5–10 minutes the water is deeply coloured.
Answer
Follow the six steps and you get a clear pink-red liquid — the red rose extract, which is your indicator.
Collect fallen petals of red roses. Do not pluck flowers; pick petals or flowers that have dropped on the ground.
Take a fistful and wash them with water to remove dust.
Crush them with a mortar and pestle so the coloured juice comes out of the cells.
Put the crushed petals in a glass tumbler and pour in enough hot water to cover them completely. Do this under adult supervision.
Cover with a lid and wait 5 – 10 minutes, till the water is well coloured.
Filter. The filtrate — the liquid you get after filtration — is the flower extract.
Why each step matters: crushing breaks open the petal cells; hot water pulls the dye out much faster than cold water; the lid keeps the steam and the smell in and stops the extract cooling too fast; and filtering removes petal bits, because a colour change is impossible to judge through a cloudy liquid.
Tip: keep the extract in a clean, covered bottle away from sunlight and use it within a day or two. A stale extract loses its colour and gives confusing results.