Science 3 Marks Question

Litmus solution is obtained from lichens. A natural dye extracted from lichens is dissolved in distilled water to obtain litmus solution.

It is used as an indicator to distinguish between acids and bases.

Solution	Colour of litmus solution
Acidic	Red
Basic	Blue
Neutral	No change

We know that basic and neutral solutions do not change the colour of blue litmus paper. Since blue litmus remains blue after dipping in the solution, the solution is either basic or neutral in nature.

Put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is neutral.

Distilled water is neutral in nature. The same can be verified by using red and blue litmus papers. Neither will show a colour change with distilled water. This proves that distilled water is neutral.

Across:

2. Neutral

4. Base

7. Red

Down:

1. Indicator

3. Turmeric

5. Acidic

6. Heat

1. 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.
2. The effect of acid can be neutralised by rubbing the affected area by baking soda solution which is a mild base.
3. Nitesh’s friends are caring, supportive and helpful.

1. Cholic acid.
2. Uric acid.
3. Nucleic acid.
4. Tartaric acid.
5. Oxalic acid.

Test tube	Effect on blue litmus paper	Effect on red litmus paper	Effect on phenolphthalein solution
A	Turns red	Remains red	Colourless
B	Remains blue	Turns blue	Pink colour
C	Remains blue	Remains red	Colourless

Dorji can use litmus test on these drinks. Just drop few drops of drink on litmus paper and take the secision according to the following:

• If it turns blue, drink is basic.
• If it turns red, drink is acidic.
• If it turns green, drink is neutral.

We know that basic and neutral solutions do not change the colour of blue litmus paper. Since blue litmus remains blue after dipping in the solution, the solution is either basic or neutral in nature. Put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is neutral.

We can use both red and blue litmus solutions to find the nature (acidic/ basic/ neutral) of each solution. In acidic media, blue litmus solution turns to red and in basic media, red litmus solution turns to blue.

Solution	Effect on red litmus solution (change in colour)	Effect on blue litmus solution (change in colour)	Nature of solution found
Sugar solution	No change	No change	Neutral
Baking soda solution	Red changes to blue color	No change	Basic
Tamarind solution	No change	Blue changes to red colour	Acidic
Salt solution (neutral)	No change	No change	Netural

Characteristics of acids are:

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

1. 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 relief from this pain. So, this information given by his teacher helped him.
2. He gave her mother 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.
3. Rahul is very intelligent and caring boy.

A small amount of hydrochloric acid produced in the stomach is useful as it can kill the harmful bacteria that may enter into the stomach along with the food.
However, if excess of 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.

Acidic in nature	Basic in nature
Vinegar	Lime water
Stomach juices	Toothpaste
Lemon juice	Baking soda solution
	Milk of magnesia
	Ammonia solution

1. Calcium hydroxide:

• It is used to make chalks.
• It is used in preparation of insecticides and fungicides.

2. Sodium hydroxide:

• It is used in manufacturing of soaps and detergents.
• It is used to manufacture paper in wood industry.

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 naturally. The excessive use of fertilisers in the fields also makes the soil too acidic. When the soil is too acidic, it is treated with base 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 it. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.

Litmus solution is obtained from lichens. A natural dye extracted from lichens is dissolved in distilled water to obtain litmus solution. It is used as an indicator to distinguish between acids and bases.

Solution	Colour of litmus solution
Acidic	Red
Basic	Blue
Neutral	No change