Is Matter around us pure Notes || Class 9 Chapter 2 Science ||
Chapter – 2
IS MATTER AROUND US PURE?
1.
If we observe some sugar and some soil (mitti) placed
on two different sheets of paper with a magnifying glass, we will find that the
colour, shape and size of all the particles of sugar are the same, but the soil
contains particles of different colours, shapes and sizes.
2.
E.g. the soil contains clay (चिकनी मिट्टी) particles, some grass particles and even some dead
insects (कीड़ा) etc.
3.
Now, sugar which contains particles of only one kind
is called a pure substance whereas soil which contains particles of different
kinds is called an impure substance (or mixture).
4.
From this we conclude that all the matter around us is
not pure.
Matter
2.
Anything which has volume & mass is called matter.
OR
3.
Any Object which is made up of atoms is called matter.
4.
The matter around us is of two types: pure and impure
(mixtures) substances.
Pure
Substances
1.
It is made up of only one kind of particles.
2.
These particles may be atoms or molecules.
3.
So, we can also say that a pure substance is one which
is made up of only one kind of atoms or molecules (2 or more atoms)
4.
E.g. Sulphur & water
5.
It is of two types – Element and Compound
Element
1.
Robert Boyle was the first scientist to use the term
element in 1661.
2.
It is made up of only one kind of atoms.
3.
E.g. hydrogen, oxygen, nitrogen, chlorine, bromine,
iodine, carbon, Sulphur, iron, copper, silver, gold, mercury and silicon, are
pure substances.
4.
Note – There are 118 elements known at present, out of
which 94 elements occur in nature, while the remaining 24 elements have been prepared
artificially, two elements are liquid at room temperature–mercury and bromine.
5.
Elements can be normally divided into metals,
non-metals and metalloids.
Metals
2.
They have silvery-grey or golden-yellow colour.
3.
Metals are generally Hard
7.
They are sonorous (make a ringing sound when hit).
8.
E.g. gold, silver, copper, iron, sodium, potassium
etc. Mercury is the only metal that is liquid at room temperature.
Non-Metal
1.
They display a variety of colours.
2.
They are poor conductors of heat and electricity (e.g.
Sulphur and phosphorus).
4.
Non-Metals are Generally Soft (except diamond)
5.
E.g. hydrogen, oxygen, iodine, carbon (coal, coke),
bromine, chlorine etc.
Metalloids
1.
The elements which show some properties of metals and
some other properties of non-metals are called metalloids.
2.
E.g. Boron (B), Silicon (Si), and Germanium (Ge)
Compound
1.
A compound is a substance made up of two or more elements
chemically combined in a fixed proportion by mass.
2.
The constituents can be separated easily by physical methods.
3.
E.g. water (H2O) is a compound made up of
two elements, hydrogen and oxygen, chemically combined in a fixed proportion of
1: 8 by mass (Atomic masses: H = 1 u, O = 16 u, so H2: O = 2 u: 16 u
or 1: 8).
4.
Other examples sand, carbon dioxide (CO2),
sodium chloride, sugar, copper sulphate, calcium oxide, sodium hydroxide,
hydrochloric acid, nitric acid, camphor, naphthalene and sand (silicon
dioxide), are pure substances.
Impure
Substances: Mixtures
1.
A mixture is one which contains two or more different
kinds of particles (atoms or molecules).
2.
In other words, a mixture contains two or more pure
substances mixed together.
3.
The constituents can be separated only by chemical or
electrochemical reactions.
4.
E.g. milk is a mixture of water, fat and proteins
5.
Other
examples are air, sugarcane (गन्ना) juice, soft drinks, sharbat, jaggery (गुड), rocks, minerals, petroleum, LPG,
biogas, tap water, tea, coffee, paint, wood, soil and bricks
6.
It is of two types – Homogeneous mixtures and
Heterogeneous mixtures
Homogeneous
mixtures
1.
Those mixtures in which the substances are completely
mixed together and cannot be separated from one another, are called homogeneous mixtures.
2.
All the homogeneous mixtures are called solutions.
3.
E.g. Sugar solution, Salt solution, Copper sulphate
solution, Seawater, Alcohol and water mixture, Petrol and oil mixture, Soda
water, Soft drinks, Lemonade, Vinegar, Brass, Air, Kerosene oil, and Petrol.
4.
Note – kerosene and petrol are not single substances,
they are mixtures of various compounds of carbon and hydrogen (called
hydrocarbons).
Heterogeneous
mixtures
1.
Those mixtures in which the substances remain separate
or don’t mixed are called heterogeneous mixtures.
2.
E.g. mixture of sugar and sand, Salt and sand mixture,
Chalk and water mixture, Muddy (कीचड़ का) river water, Flour in water etc.
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