Important Questions Class 9 Science Chapter 2 Is Matter Around Us Pure

Please refer to Is Matter Around Us Pure Class 9 Science Notes and important questions below. The Class 9 Science Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 9 Science examination questions given below to obtain better marks in exams

Is Matter Around Us Pure Class 9 Science Notes and Questions

The below Class 9 Is Matter Around Us Pure notes have been designed by expert Science teachers. These will help you a lot to understand all the important topics given in your NCERT Class 9 Science textbook.

Refer to Chapter 2 Is Matter Around Us Pure Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.

Revision Notes for Class 9 Science Chapter 2 Is Matter Around Us Pure

PURE SUBSTANCE	MIXTURE
Pure substance consists of a single type of substance.	Mixture consists of two or more pure substances.
Pure substance cannot be separated into other substances by physical methods.	Mixture can be separated into its components by physical methods.
Pure substance has its own definite properties.	Mixture shows the properties of its components.

Elements are made up of one kind of atoms only. Compounds are made up of one kind of molecules.

2. Types of Mixtures
Mixtures can also be grouped on the basis of their physical states:

	SOLID	LIQUID	GAS
SOLID	Salt and sugar	Salt and water	Dust in air
LIQUID	Mercury and copper	Alcohol and water	Clouds
GAS	Hydrogen and palladium	Oxygen and water	Air

ii) on the basis of miscibility:

Homogeneous Mixture	Heterogeneous Mixture
It consists of single phase.	It consists of two or more phase.
Uniform composition	Does not have uniform composition
Example: Sugar dissolved in water	Example: Air, sand and common salt.

4. Separating the components of a mixture
The components of a heterogeneous mixture can be separated by

• Simple methods like –hand picking , sieving , & Winnowing
• Special techniques like –

1. Evaporation : a mixture of salt and water or sugar and water.
2. Centrifugation : Butter from curd, Fine mud particles suspended in water.
3. Decantation (Using separating funnel) : Oil from water.
4. Sublimation : Camphor from salt,
5. Chromatography : Different pigments from an extract of flower petals.
6. Distillation and fractional distillation : Separating components of Petroleum
7. Magnetic separation: Iron pins from sand.

Types of Solutions

a) on the basis of size of solute particles

True solution	Sol[Colloid]	Suspension
Homogeneous	Heterogeneous	Heterogeneous
Size of solute particles is less than 1 n m or 10−9m.10−9m.	Size of solute particles is between 1 n m or 1000nm.1000nm.	Size of solute particles is more than 1000nm.1000nm.
Particles cannot pass through filter paper.	Particles cannot pass through filter paper.	Particles cannot pass through filter paper.
Stable	Stable and settle only on centrifugation	Unstable and settle down on its own.
Solution of sodium chloride in water, suger & water	Milk , Fog	Muddy water, chalk & Water, Smoke in the air.

Colloidal solution is a heterogeneous mixture. It consists of two phases:-
(i) Dispersed phase : component present in small proportion
(ii) Dispersion medium : component present in large proportion
The particles of colloid are large enough to scatter a beam of light passing through it and make its path visible. Thus, they show Tyndall effect.
The colloidal particles are moving at random in a zigzag motion in all directions.
This type of zig-zag motion of colloidal particles is called Brownian movement.

b) on the basis of amount of solute:
Unsaturated solution — A solution which has lesser amount of solute that it can dissolve at a given temperature is known as unsaturated solution.

Saturated Solution A solution which has maximum amount of solute that it can dissolve at a given temperature is known as saturated solution.

Supersaturated solution A solution which can dissolve amount of solute by increasing temperature saturated solution is known as supersaturated solution.

c) on the basis of nature of solvent
Aqueous solution The solution in which the solvent is water is known as aqueous solution

Non-Aqueous solution The solution in which the solvent is other than water (ether, alcohol or aceton) known as non-aqueous solution.

6. Physical & Chemical Changes
Physical changes – Changes that do not result in the production of a new substance.

• If you melt a block of ice, you still have H2OH2O at the end of the change.
• If you break a bottle, you still have glass.

Examples : melting, freezing, condensing, breaking, crushing, cutting, and bending.

Chemical changes – Changes that result in the production of another substance.

• As in the case of autumn leaves, a change in color is a clue to indicate a chemical change.
• a half eaten apple that turns brown.

7. Alloys
A material that has metallic properties and is composed of two or more chemical elements of which at least one is a metal .

• These cannot be separated into their components by physical methods.
• However, these are considered as mixture because these show the properties of its constituents and can have variable composition.

The benefit of alloys is that you can combine metals that have varying characteristics to create an end product that is stronger, more flexible, or otherwise desirable to manufacturers.

• Aluminium alloys are extensively used in the production of automotive engine parts.
• Copper alloys have excellent electrical and thermal performance, good corrosion resistance, high ductility and relatively low cost.
• Stainless steel alloys are used for many commercial applications such as watch straps, cutlery etc.
• Titanium alloys have high strength, toughness and stiffness & are used in aerospace structures .

You are expected to know

• Types of mixtures.
• Method of Separation of mixtures.
• Types of solutions.
• Concentration terms of solution.
• Physical and Chemical Change.
• Significance of alloys.

Questions for Class 9 Science Chapter 2 Is Matter Around Us Pure

Question. Name the process by which all dyes present in black ink be recovered.
Ans : Chromatography.

Question. How can you test the purity of a given substance?
Ans : A pure substance always has the same taste, colour or texture at particular temperature and pressure and fixed melting or boiling point. For example : Pure water boils at 100°C but if it has some impurities then water boils at a temperature above 100°C.

Question. What is decantation? Explain.
Ans : Decantation is the process of separating insoluble solids from liquids. A suspension of solid particles in a liquid is allowed to stand for sometime. Insoluble solid particles settle down at the bottom due to their weight. This is called sedimentation. The clear liquid is then transferred into another container, without disturbing the settled particles. In other words, clear liquid is decanted and separated from solid.

Question. Hydrogen is considered as element. Why?
Ans : Hydrogen have one type of element and it cannot be broken by physical or chemical process, so it is considered as element.

Question. Classify the elements.
Ans : (1) Metals, (2) Non-metals, and (3) Metalloids.

Question. Give an example of a liquid and liquid type solution.
Ans : Vinegar is a mixture of acetic acid and water.

Question. A system which have same properties throughout is called-
Ans : Homogeneous.

Question. Name the types of mixtures.
Ans : Homogeneous mixture and heterogeneous mixture.

Question. Define dispersion medium.
Ans : It is the component which is present in excess and acts as a medium in which colloidal particles are dispersed.

Question. A colloid which have liquid as dispersed phase and solid as dispersion medium called-
Ans : Gel.

Question. The component of solution that is present in smaller proportion
Ans : Solute.

Question. (i) State the principle of the process of centrifugation.
(ii) List any three applications of centrifugation.
Ans : (i) Centrifugation is the process of separating suspended particles from a liquid like colloids by churning the liquid at a high speed. The principle is that denser particles are forced to the bottom and lighter stay at the top when spun rapidly.
(ii) Applications of centrifugation :
(a) Used in dairies and homes to separate cream from milk or butter from cream.
(b) Used in washing machines to squeeze out water from clothes.
(c) Used in laboratories to separate colloidal particles from their solutions.
(d) Used in diagnostic labs for blood and urine test.

Question. Why is water considered as compound?
Ans : Water is considered as compound because :
(i) Water is composed of two elements : hydrogen and oxygen.
(ii) The ratio of hydrogen and oxygen by mass in any sample of pure water is the same.
(iii) The properties of water are different from its constituent elements : hydrogen and oxygen.
(iv) Water can be decomposed by chemical means only

Question. Write characteristics of compounds.
Ans : Characteristics of compounds :
(i) Compounds are the substances formed by chemical combination of two or more elements.
(ii) The constituent elements are present in a fixed ratio.
(iii) A chemical reaction takes place during the  formation of a compound.
(iv) Properties of a compound are different to those of its elements.
(v) Constituent elements cannot be separated by physical processes.

Question. Naphthalene and sand can be separated by the process of-
Ans : Sublimation.

Question. Name two categories of pure substance.
Ans : Element and compound.

Question. What is the meaning of ‘Kroma’? 
Ans : ‘Kroma’ means colour in Greek.

Question. Write the properties of a colloidal solution.
Ans : (i) The size of particles is too small of a colloid; vary from 1 nm to 10 nm.
(ii) Colloid is too stable thus the particles do not settle down when left undisturbed.
(iii) Particles cannot be separated from the mixture by the process of filtration.
(iv) Colloidal solutions are translucent in nature.
(v) The particles of a .colloidal solution scatter light.

Question. Give some examples where the property : malleability and ductility of metals are used in our life.
Ans : Malleability means that metals can be hammered into sheets and foils. For example : Aluminium foils are used for wrapping food stuffs, silver foils are used for decorative purposes for sweets and fruits. Ductility means that metals can be drawn into wires. Example : Gold and silver wires are used in ornaments, aluminium and copper wires are used for
conduction of electric current.

Question. What is chromatography? What is its advantage over other methods of separation?
Ans : Chromatography is the process to separate different components of a mixture by absorbing over a suitable absorber. The main advantages of this technique is :
(i) It can be used for small amount of mixture.
(ii) Component of mixture do not get wasted.
(iii) Constituent of mixture can be identified apart from separation.

Question. A homogeneous mixture of two or more substances called-
Ans : Solution.

Question. Define the term Solvent.
Ans : Component of solution that is present in the larger proportion and dissolves the other substance is called Solvent.

Question. What is condenser?
Ans : It is an apparatus which converts gas into liquid by cooling it.

Question. Name the constituents of German silver.
Ans : Copper and zinc.

Question. Define the term heterogeneous.
Ans : A substance that does not have the same properties throughout the mixture is called heterogeneous.

Question. Write the properties of a Solution.
Ans : (i) It is a homogenous mixture of solute and solvent.
(ii) Solute particles cannot be separated by filtration.
(iii) True solution is clear and transparent.
(iv) True solution does not scatter light.
(v) Solute particles cannot settle out from solvent.

Question. What makes water as a universal solvent?
Ans : Water acts as a universal solution due to :
(i) The polar nature of its molecules.
(ii) Its ability to produce soluble salt on interaction with a large number of substances.

Question. How will you separate a mixture of common salt, camphor and iron filings. Describe the process.
Ans : Mixture of common salt, camphor and iron filings :
(i) Magnet is passed over the mixture several times. Iron filings get attached to the magnet and are separated.
(ii) Camphor is separated from the salt by sublimation. Camphor is collected as sublimate and common salt is separated as residue.

Question. What are two types of matter on the basis of composition?
Ans : Pure substance and mixture.

Question. What is the principle of separation?
Ans : The difference in physical or chemical properties of components of mixture is the basis of separation.

Question. Give chemical name of chalk and quicklime.
Ans : (i) Chalk : Calcium Carbonate
(ii) Quicklime : Calcium Oxide

Question. Milk of Magnesia is a-
Ans : True solution.

Question. Name of process used to separate liquids which have difference in boiling points of less than 25°C—
Ans : Fractional distillation.

Question. Name two metals which are highly malleable and ductile.
Ans : Gold and silver.

Question. Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Ans : (i) Melting of wax changes the state of wax from solid to liquid. No new substance is formed. The chemical nature of solid wax and liquid wax is the same. Hence, melting of wax is a physical change.
(ii) Burning of wax gives new gaseous products. Both the physical and chemical changes are taking place. Hence, burning of wax is a chemical change.

Question. Name the process by which pure copper sulphate can be obtained from its impure sample.
Ans : Crystallization.

Question. Define the term heterogeneous.
Ans : A substance that does not have the same properties throughout the mixture is called heterogeneous.

Question. Define Chromatography.
Ans : The process of separation of different dissolved constituents of a mixture by absorbing them over an appropriate absorber is called, Chromatography.

Question. Write the name of any two compounds which sublime on heating.
Ans : Ammonium chloride and iodine.

Question. What is the meaning of ‘concentration of solution’?
Ans : The relative amount of solute and solvent present in a given quantity of the solution is known as the concentration of a solution.

Question. Name a metal which is liquid at room temperature.
Ans : Mercury.

Question. An element made up of only one type of—
Ans : Atom.

Question. Give two examples of colloids from your daily life.
Ans : Milk and fog.

Question. Give natural example of mixture.
Ans : Sea water, minerals, soil.