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

1.       Anything which occupies space & has mass is called matter. OR

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

1.       They are Lustrous (उजाला or चमकदार) (or Shiny) and can be Polished

2.       They have silvery-grey or golden-yellow colour.

3.       Metals are generally Hard

4.       They conduct (संचालन करना) heat and electricity.

5.       They are ductile (खींची जाने योग्य or लचीली) (can be drawn into wires).

6.       They are malleable (नरम or लचीला) (can be hammered [हथौड़े से ठोकना] into thin sheets).

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).

3.       They are not lustrous (चमकदार), sonorous or malleable (नरम or लचीला).

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.