Introduction


In this post, 
You will learn the important question and answer of chapter 2 in chemistry of class 9.

Important Question and answer of Is Matter Around us pure. 

1. What is Pure Substance? 
Answer. If a Substance is made up of only one type of particles then it is called a Pure Substance. 

2. What are the example of Pure Substance? 
Answer. Elements and compounds are the example of Pure Substance. 

3. What is impure Substance called in terms of Chemistry? 
Answer. If a Substance is made up of a combination of two different types of particles then it is called an impure Substance in term of Chemistry. 

4. Flow chart. 
Answer. 

5. What are the classification of Pure Substances? 
Answer. The classification of Pure Substance are given below:
(1) Pure Substance are made up of only one kind of particles, for example atoms and molecules. Thus all the elements are compounds and Pure Substances. 
(2) These are hemogeneous in nature. 
(3) These have constant properties such as density, melting point, boiling point, etc. 
(4) Pure Substance cannot be broken into simpler Substance (constituent particles) by any physical process. 

6. What is impure substance? 
Answer. The substance which are made by mixing two or more pure substance in any proportion are known as impure substances (mixture). 

7. What is Elements? 
Answer. Elements are those pure chemical substance which are made up of only one kind of atoms. 

8. What are the characteristic of Elements? 
Answer. (i) Elements are homogeneous in nature because they are made up of only one kind of atoms. For example, copper element is made up of copper atoms and iron element is made up of iron atoms only.

(ii) Elements cannot be broken into simpler substances by applying heat, light and electricity. For example, hydrogen is an element as it cannot be broken down into simpler substances whereas water is not an element because it can be split into hydrogen and oxygen by passing electricity.

(iii) The smallest unit of an element is atom which shows all the properties of an element. Therefore, all the atoms of an element are identical. Atoms of different elements differ in various aspects like size and composition. For example, size and composition of sodium atom is different from that of chlorine.

(iv) Elements can exist in free state (atom) or in the combined state (molecule). For example, helium, neon, argon exist in free state as He, Ne, Ar whereas chlorine, bromine, oxygen exist in combined states as Cl₂, Br, O₂.

(v) Elements can exist in solid, liquid or gaseous form. 

(vi) Two or more atoms of different elements combine together to form compounds. For example, water (H₂O) is a compound made up of hydrogen and oxygen atoms. Similarly, a number of compounds are formed by the combination of different elements. 

9. What is Metals? 
Answer. An element which is malleable, ductile and can conduct electricity is known as metal. 

10. What are non-metals? 
Answer. An elements that is either malleable nor ductile and does conduct electricity is called non-metals.