NCERT 9TH CLASS SCIENCE CHAPTER IS MATTER AROUND US PURE
DIFFERENCES BETWEEN COMPOUNDS AND MIXTURES
1. Any substance which possesses definite mass, occupies definite volume and offers resistance to external force is called matter.
2. An elementary substance contains only one kind of atoms.
3. A chemical substance which can be split into or built up from two or more dissimilar substances is called a compound.
4. All elements and compounds are homogeneous.
5. If the components mix up thoroughly in all proportions then it is called a homogeneous mixture.
6. If the components do not mix up thoroughly and can be demarcated by boundaries, then it is called a heterogeneous mixture.
7 . Compound formation is a chemical change.
Formation of a mixture is a physical change.
8. Compounds are formed by the combination of two or more elements which combine in a fixed ratio by weight.
In the formation of a mixture, no fixed ratio is maintained.
9. The constituent elements lose their individual properties.
The components retain their individual properties.
10. All compounds are homogeneous.
Mixtures may be homogeneous or heterogeneous.
11. Compounds have definite values for density, melting point and boiling point.
Mixtures do not have definite values for density, melting point and boiling point.
12. The proportion of the constituent elements is same.
The proportion of the components can be varied.
13. Compound formation is accompanied by heat energy changes.
Heat energy changes rarely occur in the preparation of mixtures.
14. The constituents are not easily separable.
The components are easily separable.
15. Compounds have definite molecular weights.
Mixtures do not have molecular weights.
All the matter around us is not pure. The matter around us is of two types : pure substances and mixtures.
A pure substance is one which is made up of only one kind of particles. All the element and compounds are pure substances because they contain only one kind of particles like hydrogen, oxygen,
chlorine, iodine, carbon, iron, copper, silver, gold are pure substances. A pure substance cannot be separated into other kinds of matter by any physical process.
Impure Substances : Mixtures
A mixture is one which contains two or more different kinds of particles (atoms or molecules). All the mixtures are impure substances because
they contain more than one kind of particles. Examples of the mixtures are : Salt solution, sugar solution, milk, sea-water.
All the matter can be divided into three general classes : elements, compounds and mixtures.