Page 32 - NCERT Science Class 10 English Medium

ou Acids in other planets
Do Y Know? The atmosphere of venus is made up of thick white and yellowish clouds of

sulphuric acid. Do you think life can exist on this planet?

What is the pH of the soil in your backyard?
Plants require a specific pH range for their healthy growth. To find out
the pH required for the healthy growth of a plant, you can collect the soil
from various places and check the pH in the manner described below in
Activity 2.12. Also, you can note down which plants are growing in the
region from which you have collected the soil.

Activity 2.122.12
Activity
2.12
Activity 2.12
Activity 2.12
Activity
n Put about 2 g soil in a test tube and add 5 mL water to it.
n Shake the contents of the test tube.
n Filter the contents and collect the filtrate in a test tube.
n Check the pH of this filtrate with the help of universal
indicator paper.
n What can you conclude about the ideal soil pH for the growth of
plants in your region?

pH in our digestive system
It is very interesting to note that our stomach produces hydrochloric
acid. It helps in the digestion of food without harming the stomach.
During indigestion the stomach produces too much acid and this causes
pain and irritation. To get rid of this pain, people use bases called
antacids. One such remedy must have been suggested by you at the
beginning of this Chapter. These antacids neutralise the excess acid.
Magnesium hydroxide (Milk of magnesia), a mild base, is often used for
this purpose.

pH change as the cause of tooth decay
Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth
enamel, made up of calcium hydroxyapatite (a crystalline form of calcium
phosphate) is the hardest substance in the body. It does not dissolve in
water, but is corroded when the pH in the mouth is below 5.5. Bacteria
present in the mouth produce acids by degradation of sugar and food
particles remaining in the mouth after eating. The best way to prevent
this is to clean the mouth after eating food. Using toothpastes, which are
generally basic, for cleaning the teeth can neutralise the excess acid and
prevent tooth decay.

Self defence by animals and plants through chemical warfare
Have you ever been stung by a honey-bee? Bee-sting leaves an acid
which causes pain and irritation. Use of a mild base like baking soda
on the stung area gives relief. Stinging hair of nettle leaves inject
methanoic acid causing burning pain.

Acids, Bases and Salts 27

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