Question

Prepare indicators by using natural materials like extract of red cabbage leaves, crushed beetroot,

Answer 1

Answer:

Y

ou have learnt in your previous classes that the sour and bitter

tastes of food are due to acids and bases, respectively, present in them.

If someone in the family is suffering from a problem of acidity after

overeating, which of the following would you suggest as a remedy– lemon

juice, vinegar or baking soda solution?

n Which property did you think of while choosing the remedy?

Surely you must have used your knowledge about the ability of

acids and bases to nullify each other’s effect.

n Recall how we tested sour and bitter substances without tasting

them.

You already know that acids are sour in taste and change the colour

of blue litmus to red, whereas, bases are bitter and change the colour of

the red litmus to blue. Litmus is a natural indicator, turmeric is another

such indicator. Have you noticed that a stain of curry on a white cloth

becomes reddish-brown when soap, which is basic in nature, is scrubbed

on it? It turns yellow again when the cloth is washed with plenty of

water. You can also use synthetic indicators such as methyl orange and

phenolphthalein to test for acids and bases.

In this Chapter, we will study the reactions of acids and bases, how

acids and bases cancel out each other’s effects and many more interesting

things that we use and see in our day-to-day life. Do You Know?

Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to

the division Thallophyta, and is commonly used as an indicator. When the litmus

solution is neither acidic nor basic, its colour is purple. There are many other natural

materials like red cabbage leaves, turmeric, coloured petals of some flowers such as

Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a

solution. These are called acid-base indicators or sometimes simply indicators.

2021–22

18 Science

2.1 UNDERSTANDING THE CHEMICAL PROPERTIES OF

ACIDS AND BASES

2.1.1 Acids and Bases in the Laboratory

Activity 2.1

These indicators tell us whether a substance is acidic or basic by

change in colour. There are some substances whose odour changes in

acidic or basic media. These are called olfactory indicators. Let us try

out some of these indicators.

Explanation: