Multiple Choice Questions

Answer: (b) add acid to water

Answer: (c) salt and water

(b) Yellow in acid and red in the base

Answer: (d) colourless and pink

Answer: (a) Organic matter

(d) the chemical change that cannot be reversed

Answer: (a) basic

Answer: (d) Curd, vinegar

Answer:(c) Turmeric

One Mark Questions

Answer: Acids turn blue litmus paper red while bases turn red litmus paper blue.

Answer: The solutions or substances which do not change the colour of either red or blue litmus paper are neutral.

1. Turmeric
2. China rose

Answer: Citric acid in lemon juice and oxalic acid in tomato.

Answer: Milk of magnesia which contains magnesium hydroxide (base) is used to neutralise the effect of excessive acid in the stomach.

Turmeric stain on white shirt is turned to red when it is washed with soap because the soap solution is basic in nature.

Answer: Lime water (calcium hydroxide) is a basic solution.

Answer: Neutralisation reaction.

Answer: The acid is formic acid that is injected into the skin of a person when an ant bites.

Answer: When hydrochloric acid reacts with sodium hydroxide solution, then sodium chloride salt is formed.

Answer: Baking soda and Soap or detergent

Answer: Carbonic acid.

Answer: Two gaseous pollutants are nitrogen dioxide (NO2) and sulphur dioxide (SO2).

Two Marks Questions

Characteristics of acids are

They are sour in taste.
They turn blue litmus paper/solution to red.
Dilution of acid in water is an exothermic reaction, i.e. heat energy is evolved.

Wasp sting injects a liquid in the skin which is acidic in nature. Hence, baking soda is the appropriate remedy as it is basic in nature and neutralises the acid.

A small amount of hydrochloric acid produced in the stomach is useful as it can kill the harmful bacteria that may enter the stomach along with the food. However, if an excess acid is produced, there is a burning sensation in the stomach. We should take milk of magnesia as an antacid medicine to neutralise the excess acid.

Answer: China rose petals when added to warm water, form a light pink coloured solution which may be used as an indicator. This indicator turns acidic solution to magenta (deep pink) and basic solution to green.

Acid can be tested in any substance by the following methods

Take a drop of the dilute solution of the substance on the tips of your tongue. If tastes sour, it is acidic.
Dip a blue litmus paper in the solution. If the colour of the litmus paper turns red, the solution is acidic.

Sodium bicarbonate neutralises the acidity in the stomach. Hence, it is used during indigestion. Lemon contains acid. It reacts with undigested food and suffers it.

In a neutralisation reaction, heat is always produced or evolved. The evolved heat raises the temperature of the reaction mixture. Therefore, if we touch the test tube immediately after the neutralisation reaction, it is found to be hot.

Acid + Base → Salt + Water (heat is evolved)

Answer: Acids which are mostly used in the laboratory as below

Hydrochloric acid (HCl)
Sulphuric acid (H2SO4)
Nitric acid (HNO3)

Answer: No, because orange juice is acidic in nature. Excess of acid in the stomach causes indigestion. We take an antacid such as milk of magnesia which contains magnesium hydroxide.

(i) Ant bite When an ant bite injects the acidic liquid (formic acid) into the skin, the effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

(ii) Indigestion Our stomach contains hydrochloric acid. It helps us to digest food but too much of acid in the stomach causes indigestion. Sometimes, indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia which contains magnesium hydroxide.

(iii) It neutralises the effect of excessive acid.


Three and Four Marks Questions

The reason for low crop yield in farmer’s field was that the soil at a place is either too acidic or too basic. The soil may be acidic or basic in nature. The excessive use of fertilisers in the fields also makes the soil too acidic. When the soil is too acidic, it is treated with bases such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralises the excess acid present in the soil and reduces its acidic nature. If the soil is too basic, then decaying organic matter (called manure or compost) is added. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.

(a) The reason for this burning pain is honeybee sting which causes pain and irritation. This is due to the acidic liquid (formic acid) injected into the skin by the honeybee.

(b) The effect of an acid can be neutralised by rubbing the affected area by baking soda solution which is a mild base.

(c) Nitesh’s friends are caring, supportive and helpful.

(a) Rahul knows that our stomach contains hydrochloric acid. It helps us to digest food. But, too much acid in the stomach causes indigestion. Sometimes, indigestion is painful and some mild base should be taken to relieve this pain. So, this information given by his teacher helped him.

(b) He gave her mother a baking soda solution which was available in the kitchen easily. He selects baking soda because it is a mild base and neutralises the excess acid in the stomach and it will give relief from pain.

(c) Rahul is a very intelligent and caring boy.