NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure in PDF form to free download. NCERT Solutions in English Medium as well as Hindi Medium free to download in PDF file format. NCERT Solutions for Class 9 Science all chapters free to download.
NCERT Solutions for Class 9 Science Chapter 2
Important Questions Based on CBSE Previous Years Papers
Class 9 Science – Is Matter Around Us Pure
- Question 1:
A diamond knife is quite often used for cutting glass. Why?
- Answer 1:
Diamond is probably the hardest substance known. Therefore, a knife made from a special type of diamond is used for cutting the glass.
- Question 2:
Give one test to show that brass is a mixture and not a compound.
- Answer 2:
When we try to melt brass, it does not have a sharp melting point. This shows that it is not a compound. It is a homogeneous mixture of copper and zinc and is called alloy.
- Question 3:
How will you justify that rusting of iron is a chemical change?
- Answer 3:
The rust is a brown chemical compound known as hydrated ferric oxide. It cannot be removed from the surface of the metal b any means. Formula of a rust shows that iron has undergone a chemical change.
- Question 4:
Explain how does soap help in cleaning dirty clothes?
- Answer 4:
In dirty clothes, the dust particles are present on oil are present on oil drops sticking to them. Simple water cannot remove these oil drops from the clothes because water and oil as such do not form a stable emulsion. Soap plays the role of emulsifier and helps in forming a stable emulsion between the two. This means that soap helps in removing these oil drops along with the dirt sticking to them. The dirty clothes get washed by soap solution.
- Question 5:
Colloidal solution show Tyndall effect but true solution do not. Discuss.
- Answer 5:
In a colloidal solution, the particle size is such (1 nn to 100 nm), that these particles scatter the light rays as they fall on them. Because of scattering the path of the light as well as the particle become visible. But in a true solution, the particle size is so small (less than 1 nm) that these particles are not in a position to scatter the light. Therefore, true solution does not show any Tyndall effect.
- Question 6:
Why do not the dispersed phase particles in a colloidal solution combine with one other?
- Answer 6:
They do not come closer because of the presence of either positive or negative charge on them. Due to mutual repulsion, these particles remain scattered in a colloidal solution.
- Question 7:
What is the function of fractionating column in fractional distillation?
- Answer 7:
A fractionating column obstructs the upwards movement of the vapours of the liquids. As a result, the energy (latent heat of fusion) which is released by the high boiling liquid is taken by the low boiling liquid. It remains in the vapours state. The high boiling liquid by releasing energy condenses and falls back in the distillation flask. Thus, fractionating column helps in the separation of the components from a mixture.
- Question 8:
Alloys are sometimes called substitutional solid solutions. Explain.
- Answer 8:
Alloys are the homogeneous mixtures of two or more metals. For example, brass is a mixture of copper and zinc. Actually, copper is a crystalline solid in which the atoms are closely packed to form a crystal lattice. Some of these atoms have been replaced or substituted by atoms of zinc. Therefore, brass is regarded as a substitutional solid solution.
- Question 9:
What are the units of mass percent?
- Answer 9:
Mass percent has no units as it is simply a ratio.
- Question 10:
All mixtures are homogeneous. Is this statement correct? Justify your answer.
- Answer 10:
No, this statement is wrong. Mixture because they have combined with each other to form ammonium chloride which is a new substance. A mixture is always formed by mixing non-reacting substances.
Ammonia (gas) + Hydrogen chloride (gas) → Ammonium chloride (solid).