Paheli Boojho Acids Bases & Salt Class 7 Science chapter 5:
1. Can I taste all substances to find their taste?
Answer: Some substances are edible, some are tasteless, sweet, sour etc. But there are many substances that are corrosive e.g. acids and bases; some may be poisonous while others may be bitter or non-edible. So, we should taste every substance which we see. Instead, we should taste the substances that we already know well or our parents/guardians have told us.
2. Why turmeric turns red with soap?
Some substances turn their colour when they’re put in acidic or basic solution. These substances are called acid-base indicators. Turmeric is a natural acid-base indicator. In a natural or acidic state, it is yellow. In a basic condition like soap solution, it turns red.
Interesting workout: Soak a paper in turmeric solution and let it dry. Now you can use a soap solution to draw some red flowers on the sheet.
3. I am not getting the same result when using solid baking soda on dry litmus paper. Why?
Litmus paper is an acid-base indicator. The acidic solution turns the blue litmus to red and the bases turn the red litmus paper to blue. To do this they need a liquid water medium. Solid baking soda does not contain water, nor dry litmus paper. As a result, we do not see changes in the colour of dry litmus paper with dry baking soda.