15
– Materials we use
Q. 1. Fill in the blanks using appropriate words :
(white
cement, soap, detergent, wearing of bones, tooth decay, hard, soft, Portland,
fatty acid.)
(1) The substance that helps water to remove dirt from
the surface of materials is called ………....
(2) Fluoride is used in toothpaste to prevent ........
(3) Soap is a salt of ..................... and sodium
hydroxide.
(4) Synthetic detergents can be used in ..............
..... water as well.
(5) For construction purposes. ................ cement is
the most commonly used cement. Ans. (1) detergent (2) tooth decay (3) fatty
acid (4) hard (5) Portland.
Q. 2. What are the similarities and differences between
the following:
(1) Natural
detergents and man-made detergents.
Ans. Similarities : Both are used for cleaning.
Differences :
Natural
detergents
Man-made detergents
1. Natural
detergents are naturally present 1. Man-made detergents are substances
substances. produced
by man.
2. Natural
detergents contain a chemical 2.
Man-made detergents contain additives named saponin. such
as perfumes, dyes, germicides,
alcohol, anti-foaming agents, moisturizers,
fine sand etc.
3. Natural
detergents do not have any 3. Man-made detergents may have harmful
harmful effect on clothes or skin. effects on skin and clothes.
4. Natural detergents do not
cause pollution 4. Man-made
detergents cause pollution of water bodies. water bodies.
e.g., Soap nut and soap pod e.g., Different
synthetic detergents.
(2) Soap and synthetic detergents.
Ans. Similarities : Both are used for cleaning.
Differences :
Soap Synthetic detergents
1. Soaps are made by adding sodium 1. Synthetic detergents are made from
hydroxide or potassium hydroxide, kerosene and fats.
coconut oil,
salt etc.
2. Soaps do not produce lather in hard 2. Synthetic detergents produce lather
in water.
hard water too.
3. Simple soaps may not clean the clothes 3. Synthetic detergents clean the clothes
effectively
effectively.
4. Mild soaps are not harmful for the skin. 4. Synthetic detergents are harmful for the
skin.
(3) Bath soap and soap for washing clothes.
Ans. Similarities : Both the soaps contain fatty acids
and both are used for cleansing. Differences :
Bath
soap Soap
for washing clothes
1.Bath soap is used for personal cleanliness. 1. Soap for
washing clothes keeps
clothes clean.
2. This soap is mild 2. It is a hard soap.
3. This is a potassium salt of fatty acids 3. This is a sodium salt of fatty acids.
(4) Modern cement and ancient cement.
Ans. Similarities : Both are used for construction work.
Differences :
Modern
cement Ancient cement
Modern cement is made from silica (sand), Aqueous cement is made by mixing
alumina (aluminium oxide), lime, iron volcanic ash in moistened lime.
oxide and magnesia (magnesium oxide)
Q. 3. Answer the following questions in one sentences :
(1) What should be expected from a detergent for delicate
garments?
Ans. Soap
nut and soap pod are the best detergent for the delicate garments, as they do
not have any harmful effect on delicate silk and woollen threads and cloth.
(2) How will you check with the help of soap powder
whether water is hard?
Ans. The
soap does not produce foam in hard water, due to the dissolved salts in the
hard water. Thus by using soap powder we can understand if water is hard.
Q. 4. Answer
the following questions in short:
(1) What are
the important ingredients of a toothpaste, and what is the function of each?
Ans. The
important ingredients of a toothpaste are calcium carbonate and calcium
hydrogen phosphate. These substances remove the dirt from the teeth. They also
help to polish the teeth. Fluoride is also added to toothpaste. This prevents
the tooth decay. Fluoride makes the enamel of the teeth strong.
(2) How does
the use of a detergent help to clean soiled clothes?
Ans.
Detergents are used to clean the dirt and oily stains on the clothes. The
molecules of detergent are long in their structure. This molecule holds on to a
water molecule on one of its side and the oil molecule onto the other. Due to
this the oil mixes with water. It can easily come out of cloth along with dirt.
The soiled clothes thus become clean due to detergent.
(3) What is meant by 'surface activity? Name three
chemicals responsible for the surface activity of various detergents.
Ans. The
property of a substance of spreading on a surface is called surface activity.
The substances
showing this property are called surfactant.
The
chemicals added to detergents which make them surfactants are petroleum
products such as kerosene, fats, sulphur trioxide, alcohol etc.
(4) What are
the ingredients of cement?
Ans. The ingredients of simple cement are silica
(sand), alumina (aluminium oxide) lime, iron oxide and magnesia (magnesium
oxide). In Portland cement, there is 60% lime (calcium oxide), 25% silica
(silicon dioxide), 5% alumina and remaining iron oxide and gypsum
(calcium sulphate).
(5) What will happen if cement
is not used in making concrete?
Ans.
Concrete is prepared by mixing cement. water, sand and gravel. If cement is
lacking in this mixture, the construction work will not become rigid. Cement is useful in preventing leakage. A strong and
leak proof slab is possible only due to high quality cement mixed in concrete.
If cement is not used while making concrete, there will be leakage the slabs
and pillars will not be strong and the building will collapse.
Q. 5. Give scientific reasons:
(1) Soap cannot be used in hard water
Ans. There
are different types of salts in the hard water. Therefore soap does not give
lather but forms a scum. Due to scum soap loses its cleansing property.
Therefore, soap cannot be used in hard water.
(2) Oil does not mix in water. However, oil and water become homogenous
if a sufficient quantity of detergent is added.
Ans. The
detergent is a long molecule with two ends. At one end it holds the oil
molecule while at the other end it holds the water molecule. This makes a
mixture of oil and water. he result is homogenous mixture. Thus normally oil
and water will not mix. But addition of detergent makes the homogenous mixture
of oil and water.
(3) Synthetic detergents are superior to soap.
Ans. The synthetic detergents can be used in hard water. There are many
additives such as germicides, alcohol, anti-foaming agents, moisturizers, fine
sand, etc. mixed with different detergents. These supportive substances make
synthetic detergents more useful than a soap and thus they are superior to soap.
(4) Often coloured spots are formed on clothes during washing.
Ans.
Sometimes impurities in the soap can form the spots on clothes. Some spots like
thee of turmeric become red upon the action of soap. Thus coloured spots are
seen during washing.
(5) Tobacco
masheri should not be used for cleaning teeth
Ans. Tobacco is a harmful substance for the health.It
can cause addiction and cancer.
Masheri made up of tobacco can cause harmful effects on
teeth masheri should not be used for
cleaning teeth.
