Solutions-Class 7-Science-Chapter-15-Material We Use-Maharashtra Board

(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.

• Detergent is a cleansing agent that used to clean the dirt and oily stains.
• Detergent molecules 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 holds water molecule while the other end holds oil and dirt. This results in the mixing of oil and dirt with water.
• Due to the ability to get attached to both oil and water, detergent molecule spreads easily and oil easily come out of cloth along with dirt .
• This property of a substance expanding on a surface is known as surface activity and the substance is known as surfactant.

The soiled clothes thus becomes clean due to detergent.
 

Soap can be used to check weather sample of water is hard or soft. Soaps do not produce foam with hard water due to the dissolved salts in the hard water. If we do not get formation of foam in water while using soap, we can say it is hard water.

The important ingredients of a toothpaste are  calcium carbonate and calcium hydrogen phosphates which help to remove the dirt on teeth and also helps to polish them. Fluoride is also the most common active ingredients used to prevent decay of our teeth. It helps in strengthening of bones and the enamel which covers the teeth.
 

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. In Portland cement there is 60% lime, 25% silica, 5% alumina and remaining iron oxide and gypsum.

• 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 leak-proof.
• A strong and leak-proof slab is possible only due to high quality cement mixed in concrete.
• If cement is not mixed then there will be the chances of collapsing of building or structure.

The detergents which we use in our daily lives are-

• For Hair wash -Shampoo, Ritha and Shikhakai for washing hair
• For Bathing - Soaps like Moti, Lux etc.
• For cloth washing-Detergent powder like Nirma, Tide etc.

A delicate detergent should clean the clothes effectively, remove all kinds of stains without causing any harm to the clothes and maintain the quality of the clothes. Soap nut and soap pod are the best detergent for delicate garments.
 

• Surface activity of a substance is the property of a substance of spread on a surface. For example, soap water easily spreads on the any kind of surface and thus is used for cleaning purpose.
• The substance showing surface activity are called surfactant.
• Chemicals added for the surface activity to various detergents are alkylbenzene sulphonate, alcohol, kerosene etc.

Similarities : Both are used for cleaning purpose

Differences :

Similarities: Both are used for cleaning purpose

Differences :

Similarities: Both contain fatty acid and both are used for cleaning purpose

Differences :

Similarities: Both used for construction purpose

Differences :

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.
 

Normally Oil and water do not mix they are two immiscible liquids which means both of them repel each other. But when we add a detergent to a solution containing water and oil, the mixture becomes homogeneous. 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 oil molecule. This property of detergent helps in dissolving the oil in water and thus making a homogeneous mixture.

• Synthetic detergents are superior to soap because synthetic detergents work both in soft water and hard water.
• There are many additives such as alcohol, anti-foaming agent, germicides etc. mixed with different detergents, it makes it more useful.
• In contrast, soaps work only in soft water and they are not effective in hard water.
• Thus synthetic detergents are superior to soap.

• Sometime impurities present in soap can cause to form spots on the cloths.
• Toothpaste, deodorants, hair sprays, strong perfumes with alcohol turmeric are often the cause of stains on garments, some of these appears upon the action of soap.
• Thus colored spots are seen during washing.

Tobacco has various kinds of negative effects on our body. Masheri made up of tobacco. It should not be used for cleaning teeth because it can harm to 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.