(h) What is meant by 'surface activity'?
Name three chemicals responsible
for the surface activity of various
detergents.
Answers
Explanation:
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Page No 103:
Question 1:
Fill appropriate terms in the blanks .
( white cement , soap, detergent , wearing of bones, tooth decay, hard, soft, Portland, fatty acid )
(a) The substance that helps water to remove dirt from the surface of materials is called ............... .
(b) Fluoride is used in toothpaste to prevent ................ .
(c) Soap is a salt of ............... and sodium hydroxide.
(d) Synthetic detergents can be used in .............. water as well .
(e) For construction purposes ............... cement is the most commonly used cement.
ANSWER:
(a) The substance that helps water to remove dirt from the surface of materials is called detergent.
(b) Fluoride is used in toothpaste to prevent tooth decay.
(c) Soap is a salt of fatty acid and sodium hydroxide.
(d) Synthetic detergents can be used in hard water as well.
(e) For construction purposes Portland cement is the most commonly used cement.
Page No 103:
Question 2:
Write answer to the following questions.
(a) How does the use of a detergent help to clean soiled clothes ?
(b) How will you check with the help of soap powder whether water is hard ?
(c) What are the important ingredients of a toothpaste , and what is the function of each ?
(d) What are the ingredients of cements ?
(e) What will happen if cement is not used in making concrete ?
(f) Make a list of detergents that you use.
(g) What should be expected from a detergent for delicate garments ?
(h) What is meant by ' surface activity'? Name three chemicals responsible for the surface activity of various detergents.
ANSWER:
a. Detergent is a cleansing agent that combines with the impurities to make them more soluble and therefore wipe them away. A molecule of detergent consists of two ends. One of its ends is attracted towards the water while the other holds on to the dirt. This results in the mixing of dirt and water. Due to the ability to get attached to both oil and water, detergent molecule spreads easily. This property of a substance expanding on a surface is known as surface activity and the substance is known as surfactant. One of the effects of surface activity is lather formation.
This action of detergent molecule results in the remoal of dirt and stains from the clothes.
b. Soap can be used to check wether sample of water is hard or soft. Soaps do not give lather with hard water instead form scum whereas they give lather with soft water. If we do not get lather in water while using soap, we can say it is hard water.
c. The important ingredients of a toothpaste are abrasives, water and fluoride. Abrasives such as calcium carbonate and calcium hydrogen phosphates help to remove the dirt on teeth and also helps to polish them. Fluoride is the most common active ingredients used to prevent decay of our teeth. It helps in strenghtening of bones and the enamel which covers the teeth.
d. The ingredients of cement are lime (CaO), clay, silica along with some other oxides of aluminium, iron and magnesium. Gypsum (CaSO4, 2H2O) is usually added to regulate the setting rate of cement.
e. Concrete is a mixture of cement, water, sand and gravel. Cement helps in making the structures strong and leak proof. If cement is not mixed in concrete, the structures made using concrete will not be strong and leakproof and thus will have the chances of falling down.
f. The detergents which we use in our daily lives are-
ritha and shikhakai for washing hair
soaps like dettol, dove, lifeboy etc. for bathing
detergents like surf excel, tide etc. for washing clothes
g. A delicate detergent should clean the clothes effectively without affecting the quality of the clothes. It should have the ability to remove all kinds of stains without causing any harm to the clothes.
h. Surface activity of a substance is the property by virtue of which it can spread on a surface. For example, soap water easily spreads on the any kind of surface and thus is used for cleaning purpose. Chemicals responsible for the surface activity of various detergents are alkylbenzene sulphonate, alcohol ethoxysulphates and alkyl sulphates