Is Matter Around Us Pure?

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Chapter 2 MONDAY, JULY 16, 2012
Chapter 3 CBSE - Class 9 - CH2 - Is Matter Around Us Pure

Q1: On the basis of composition, how matter is classified?

Answer:
* Pure Subtance
* Mixture

Q2(NCERT): What is meant by a pure substance?

Answer: A sample of matter containing only one substance is called a pure substance. In other words all constituents of the substance are same in their chemical nature.

Q3: What are the characteristics exhibited by a pure substance?

Answer: 
1. A pure substance contains only one kind of atoms or molecules. 2. It is perfectly homogenous
3. It has definite composition which does not vary with time. 4. It has definite melting point, boiling point, density etc. Q4: What are different categories of pure substance?
Answer:
* Elements
* Compounds
Q5: Name two properties of a substance to check its purity?

Answer: A pure substance has a fixed melting point or boiling point at constant pressure. The purity of a substance can be tested by checking its melting point or boiling point. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will change.

Q6: Define mixture.

Answer: If two or more substances (elements or compounds) are mixed together in any proportion, do not undergo any chemical change but retain their properties, the resulting substance is called mixture.

Q7: What are the kinds of mixture?

Answer:
* Homogenous mixture
* Hetrogenous mixture
Q8: What are the characteristics of mixture?

Answer:

1.  Variable composition: The constituents of a mixture are present in any ratio. Example: A mixture of sand and salt can be in a ratio of 1:2 or 1:3 by weight. 

2. Only Physical change: The mixture is a result of physical change. The constituents of a mixture do not bind each other by chemical bonds. Example: In air the main constituents, i.e., oxygen, nitrogen and carbon dioxide, do not bind each other with chemical bonds. 

3. No specific properties: The properties of a mixture are the average of the properties of its constituents. Example: The properties of air are average common properties of nitrogen and oxygen. 

4.  Homogeneity: Most of the mixtures are heterogeneous, i.e., their constituents are not spread evenly throughout. However, some mixtures are homogeneous i.e. constituents are uniformly spread out. Example: In the mixture of iron and sulphur, at some places iron is more and at some places sulphur is more. 

5.  Separation Methods: In general, the constituents of mixture can be separated by applying suitable physical methods. E.g. Iron can be separated from the mixture of iron and sulphur with the help of a magnet. 

6.  Energy changes: In general, no energy is released or absorbed during the formation of a mixture.  Example: On mixing iron and sulphur, heat energy is neither absorbed nor evolved. 

Q 9: List the points of differences between homogeneous and heterogeneous mixtures.

Answer:
Homogenous Mixture           | Heterogeneous Mixture| 1....
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