Chapter 15 - Materials we Use
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 ………..
Ans: detergent
(b) Fluoride is used in toothpaste to prevent …….
Ans: tooth decay
(c) Soap is a salt of ……….. and sodium hydroxide.
Ans: fatty acid
(d) Synthetic detergents can be used in ……….. water as well.
Ans: hard
(e) For construction purposes …………. cement is the most commonly used cement.
Ans: Portland
2. Write answers to the following questions.
(a) How does the use of a detergent help to clean soiled clothes ?
Ans: The molecules of a detergent are long, and the properties of their two ends are different. A detergent molecule holds on to a water molecule at one end and an oil molecule at the other. As a result, the molecules of oil mixed with the water. This is how detergent acts when we wash our soiled clothes.
(b) How will you check with the help of soap powder whether water is hard ?
Ans: In hard water, soap does not give off lather but forms a scum. Thus, by using soap powder, we can understand whether water is hard or not.
(c) What are the important ingredients of a toothpaste, and what is the function of each?
Ans: The principal ingredients of toothpaste are calcium carbonate and calcium hydrogen phosphate. These substances remove the dirt and also polish the teeth. A certain proportion of fluoride in the toothpaste helps prevent tooth decay. It is essential for the strengthening of bones and the enamel covering of teeth.
(d) What are the ingredients of cement ?
Ans: Cement is made from silica (sand), alumina (aluminium oxide), lime, iron oxide, and magnesia (magnesium oxide). Portland cement is the most commonly used cement and is made from raw material that consists of 60% lime (calcium oxide), 25% silica (silicon dioxide), and 5% alumina.
(e) What will happen if cement is not used in making concrete ?
Ans:
Concrete is prepared by mixing cement, water, sand, and gravel. Cement is useful in preventing leakage. A strong and leak-proof slab is possible only due to the high-quality cement mixed in the 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.
(f) Make a list of detergents that you use.
Ans:
For washing our hair, we use Head and Shoulders shampoo and conditioner, Dove shampoo and conditioner, etc.
For bathing, we use soaps like Lifebuoy, Dettol, Dove, etc.
For washing clothes, we use detergents like Rin, Tide, Surf-Excel, etc.
(g) What should be expected from a detergent for delicate garments ?
Ans:
For delicate garments, the detergents should clean the clothes without affecting the quality of the fabric. Soap nut (ritha) and soap pod (shikekai) are natural detergents that are safe for human skin as well as silk and woollen threads and cloth.
(h) What is meant by ‘surface activity’ ? Name three chemicals responsible for the surface activity of various detergents.
Ans:
The property of a substance spreading on a surface is called surface activity, and the substance is said to be a surfactant. The chemicals responsible for the surface activity of various detergents are petroleum products such as kerosene, fats, sulphur dioxide, alcohol, etc.
3. What are the similarities and differences between –
(a) Natural detergents and man-made detergents
Ans:
Similarities – Both are used for cleaning.
Differences –
| Natural detergents | Man-made detergents |
|---|---|
(i) Natural detergents contain naturally occurring substances. | (i) Man-made detergents are substances produced by man. |
(ii) Natural detergents contain a chemical named saponin. | (ii) Man-made detergents contain additives such as perfumes, dyes, germicides, alcohol, anti-foaming agents, moisturizers, fine sand etc. |
(iii) Natural detergents do not have any harmful effects on clothes or skin. | (iii) Man-made detergents may have harmful effects on skin and clothes. |
(iv) Natural detergents do not cause pollution of water bodies. | (iv) Man-made detergents cause pollution of water bodies. |
e.g., Soap nut and soap pod | e.g., different synthetic detergents |
(b) Soap and synthetic detergent.
Ans:
Similarities – Both are used for cleaning.
Differences –
| Soap | Synthetic detergents |
|---|---|
(i) Soaps are made by adding sodium hydroxide or potassium hydroxide, coconut oil, salt, etc. | (i) Synthetic detergents are made from kerosene and fats. |
(ii) Soaps do not produce lather in hard water. | (ii) Synthetic detergents produce lather in hard water too. |
(iii) Simple soaps may not clean the clothes effectively. | (iii) Synthetic detergents clean the clothes effectively. |
(iv) Mild soaps are not harmful for the skin. | (iv) Synthetic detergents are harmful for the skin. |
(c) 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 |
|---|---|
(i) Bath soap is used for personal cleanliness. | (i) Soap for washing clothes keeps the clothes clean. |
(ii) This soap is mild. | (ii) It is a hard soap. |
(iii) This is a potassium salt of fatty acids. | (iii) This is a sodium salt of fatty acids. |
(d) Modern cement and ancient cement.
Ans:
Similarities – Both are used for construction work.
Differences –
| Modern cement | Ancient cement |
|---|---|
(i) Modern cement was developed by a British scientsit, John Smeaton. | (i) Ancient cement was developed by the Romans during the Roman empire |
(ii) It is made from silica (sand), alumina (aluminium oxide), lime, iron oxide, and magnesium oxide. | (ii) It is made by mixing volcanic ash with moistened lime. |
4. Explain why –
(a) Soap cannot be used in hard water.
Ans: In the hard water, soap does not give lather but forms a scum. As a result, soap loses its cleansing property. Hence, 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.
Ans: Oil and water are two immiscible liquids which means both of them repel each other. The detergent molecules have two ends. One of its ends holds on to a water molecule and the other end holds on to the oil molecule. As a result the molecules of oil mix with the water, and we will see that the water and oil have become homogenous and the colour of the mixture appears milky.
(c) Synthetic detergents are superior to soap.
Ans: Synthetic detergents are superior to soap because synthetic detergents work both in soft water and hard water as the calcium and magnesium salts of detergents are soluble in water. In contrast, soaps work only in soft water and they are not effective in hard water.
(d) Often coloured spots are formed on clothes during washing.
Ans: Soaps are sodium salts of fatty acids and are basic in nature. While washing the clothes, turmeric reacts with the soap solution and turns red, forming red spots on the clothes. But the spots disappear after washing the clothes with plenty of water.
(e) Tobacco masheri should not be used for cleaning teeth.
Ans: Tobacco masheri is a tooth cleaning powder used for the purpose of cleaning teeth. It contains tobacco. Tobacco has various kinds of negative effects on our body. It should not be used for cleaning teeth because it can harm the 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.