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७ वी सामान्य विज्ञान 15.Materials we Use पदार्थ : आपल्या वापरातील

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 1:

(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.

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 2:

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.

Question 3:

What are the similarities and difference between -

(a) Natural detergents and man-made detergents

(b) Soap and synthetic detergent 

(c) Bath soap and soap for washing clothes 

(d) Modern cement and ancient cement 

Answer 3:


Natural detergents
Man made detergents

1.Natural detergents refer to the substances which are naturally available and can be used as detergents.
Man made detergents are detergents which have been made by humans for their use.

2. Examples of natural detergents include soap nut (ritha) and soap pod (shikhakai).
Example of man made detergent is soap.


Synthetic detergent

1. Soaps are sodium salt of fatty acids (soft soap) or potassium salts of fatty acids (hard soap).
Synthetic detergents are made up of raw materials like fats or kerosene.

2. They can be used only with soft water.
They can be used with both soft and hard water.


Bath soap
Soap for washing clothes

1. It is a type of soft soap and used for bathing purposes.
It is a type of hard soap and is used for washing clothes.

2. Soft soaps are sodium salt of fatty acids.
Hard soaps are potassium salts of fatty acids.


Ancient cement
Modern cement

1. It was developed by the Romans during the
Roman empire.
It was developed by a British sceintist, John Smeaton.
2. It was prepared by mixig volcanic ash in moistened lime.
It is made up of materials like lime (CaO), clay, silica along with some other oxides of aluminium, iron and magnesium and gypsum (CaSO4, 2H2O).

Question 4:

Explain Why -

(a) Soap cannot be used in hard water .
(b) Oil does not mix in water . However, oil and water become homogeneous if a sufficient quantity of detergent is added .
(c) Synthetic detergents are superior to soap .
(d) Often coloured spots are formed on clothes during washing .
(e) Tobacco masheri​ should not be used for cleaning teeth.

Answer 4:

a. Soaps cannot be used in hard water because they lose their cleansing property when used with it. Soaps do not form lather with hard water and instead forms scum, as a result of which it loses its cleansing property.

b. Oil and water are two immiscible liquids which means both of them repel each other. But when we add a detegent to a solution conatining water and oil, the mixture becomes homogeneuos. This happens because of the detergent molecule. The detergent molecules have two ends. One of its end holds on to a water molecule and the other end holds on to the oil molecule. These opposing forces helps in dissolving the oil in water and thus making a homogeneous mixture.

c. Synthetic detergents are superior to soap because synthetic detergents work both in soft water and hard water. In contrast, soaps work only in soft water and they are not effective in hard water. 

d. The laundry, skin care, beauty and personal hygiene products which we use commonly can cause stains and color changes in our clothes. Toothpaste, perspiration, facial soap, deodorants, hair sprays, strong perfumes with alcohol and even rain are often the cause of stains on garments. All these stains may eventually dry up not causing any visible stain however, age and exposure to heat will cause them to reappear.

e. Tobacco has various kinds of negative effects on our body. It should not be used for cleaning teeths becuase it can harm th soft and hard tissues of our mouth. Use of tobacco poses serious risks like oral cancer, gum disease, poor healing after surgery, receding gums, and tooth decay.
७ वी सामान्य विज्ञान 15.Materials we Use पदार्थ : आपल्या वापरातील ७ वी सामान्य विज्ञान 15.Materials we Use पदार्थ : आपल्या वापरातील Reviewed by Amol Uge on January 08, 2019 Rating: 5
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