Answer the following questions:[3 M]

Question 13 Marks

What causes the hardness of water?

Answer

Hardness is a measure of amount of dissolved salts in water.
It is caused by dissolved salts like carbonates, chlorides mostly of calcium and magnesium
Presence of these makes washing of clothes by soap difficult.
Hard water is water that has high mineral content.
Hard water is formed when water percolates through deposits of limestone and chalk.

Question 23 Marks

What is meant by surface activity? Name three chemicals responsible for the surface activity of various detergents.

Answer

Due to the property of holding on to both oil and water, soap water spreads easily on many types of surfaces.
The property of a substance of spreading on a surface is called surface activity and the substance is called surfactant.
Detergents are surface active.
They increase the spreading and wetting ability of water by reducing its surface tension.
Chemicals responsible for the surface activity of various detergents is phenol, Aprotinin.

Question 33 Marks

Make a list of detergents, that you use.

Answer

There are two types of detergents that we use, (a) Natural (b) Man-made detergents.

Natural detergents are soap nut (ritha) soap pod (shikekai).
Man-made detergents are soap, hard soaps, soft soaps.
Synthetic detergents have taken the place of soap.
- Detergents are commonly available as powders or concentrated solution.
- Detergents are for laundry, washing clothes and cleaning dishes.
Alkaline detergents used for hard surface cleaning.

Question 43 Marks

What are the important ingredients of a tooth paste and what is the function of each?

Answer

The important ingredients of a toothpaste are calcium carbonate and calcium hydrogen phosphate.
They remove the dirt on teeth. These ingredients also polish the teeth.
A certain proportion of fluoride in the tooth paste helps prevent tooth decay.
It is essential for the enamel covering of teeth.

Question 53 Marks

Tobacco masheri should not be used for cleaning teeth.

Answer

Masheri is the smokeless form of tobacco. It is tobacco, containing teeth cleaning powder
It contains tobacco leaves.
Tobacco contains toxic and Carcinogenic chemicals which can cause cancer, oral cancer, mouth and throat cancer, gum disease, tooth decay.
Its use can cause abnormal delivery in pregnant women.

Question 63 Marks

Often coloured spots are formed on clothes during washing.

Answer

Curry stains stick fast to the criss-crossing threads of the material of our clothes.
Curry contains turmeric a natural indicator which turns red in a basic solution.
Soaps are sodium salts of fatty acids and are basic in nature.
While washing the clothes, turmeric reacts with soap solution and turns red forming red spots on the clothes.
But the spots disappear after washing the clothes with plenty of water.

Question 73 Marks

Synthetic detergents are superior to soap.

Answer

Soap is a man-made detergent which has been in use since ancient times.
It was prepared by using animal fat and wood ash. In hard water, soap does not give lather, it loses its cleansing property.
So we can not use soap in hard water. Now synthetic detergents have taken the place of soap.
They can be used in hard water as well
Synthetic detergents have many more advanced properties like they are added with perfumes, conditioner for fabric, etc.

Question 83 Marks

Oil does not mix in water. However, oil and water become homogenous if a sufficient quantity of detergent is added.

Answer

A molecule of a detergent holds on to a water molecule at one end and an oil molecule at the other.
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.

Question 93 Marks

Soap cannot be used in hard water.

Answer

In the hard water of a well or a tube well, soap does not give lather but forms a scum.
As a result soap loses its cleansing property. So soap cannot be used in hard water.

Science Answer the following questions:[3 M]