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Elements are made up of one kind of atoms only. Compounds are made up of one kind of molecules only.
Difference between Compound &Mixture
[ Refer NCERT text Book Tab.2.2, page 26]
Q.1 Is air around us a compound or mixture?
2. Types of Mixtures Mixtures can also be grouped
i) On the basis of their physical states:
ii) On the basis of miscibility:
i) Solid/solid (homogeneous)
ii) Solid/solid (heterogeneous)
iii) Liquid/liquid (homogeneous)
v) Gas/liquid (homogeneous)..
Q.2 Classify the following as homogeneous & heterogeneous mixture:
i) sodium chloride & water
ii) glucose & water
iii) sand & water
4. Separating the components of a mixture
The components of a heterogeneous mixture can be separated by
1.Simple methods like :-
hand picking , sieving , & Winnowing
2.Special techniques like: -
i) Evaporation : a mixture of salt and water or sugar and water.
ii) Centrifugation : Butter from curd, Fine mud particles suspended in water.
iii) Decantation (Using separating funnel) : Oil from water.
iv) Sublimation : Camphor from salt,
v) Chromatography : Different pigments from an extract of flower petals.
vi) Distillation and fractional distillation : Separating components of Petroleum
vii) Magnetic separation: Iron pins from sand.
Q.1 Name the process you would use to :
Q.2 How will you separate a mixture of sand , water and mustard oil ?
5. Concentration of Solution
The amount of solute present in a given amount (mass or volume) of solution.
The concentration of a solution can be expressed as mass by mass percentage or as mass by volume percentage.
Types of Solutions
a) on the basis of size of solute particles:
Chemistry Class 9 Notes Chapter 2 is matter around us pure (www.ncerthelp.com)
[ Types of colloids : refer NCERT Text Book table 2.1 , page 18 ]
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:
c) On the basis of nature of solvent
Q.1 Classify the following substances into true solutions and colloidal solutions.
Milk , ink , starch dissolved in water.
6.Physical & Chemical Changes
Changes that do not result in the production of a new substance.
• If you melt a block of ice, you still have H2O at the end of the change.
Examples : melting, freezing, condensing, breaking, crushing, cutting, and bending.
- 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.
Q.1 Which of the following is an example of physical change?
a. Mixing baking soda and vinegar together, and this causes bubbles and foam.
b. A glass cup falls from the counter and shatters on the ground.
c. Lighting a piece of paper on fire and the paper burns up and leaves ashes.
d. Baking a birthday cake for your mother.
Q.2. Which of the following is an example of chemical change?
a. Filling up a balloon with hot air.
b. Taking a glass of water and freezing it by placing it in the freezer.
c. A plant collecting sunlight and turning it into food.
d. Your dog ripping up your homework.
Q3. Which change can be easily be reversed?
a. Chemical Change
b. Physical Change
c. Both a physical and chemical change
d. Neither a physical or chemical change
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
Q,1 Why should we use alloys instead of pure metals?
Q.2 State uses of Aluminium & Stainless steel alloys.
QUESTION BANK [ *HOTS ]
1 Mark Questions:
1. What is meant by pure substance?
2. What is meant by mass percentage of solution?
3. Name the process of separation of miscible liquids.
4. Arrange the following in decreasing order of size of the particles.
5. *Give an example of an aqueous solution in which gas is dissolved.
6. Name the dispersion medium and dispersed phase in the white material inside an egg.
7. What happens when hot saturated solution is cooled?
8. How would you separate a mixture of chalk and water?
9. *How much water should be added to 15 grams of salt to obtain 15 % salt solution?
10. What type of mixtures are separated by technique of crystallization ?
1. Classify the following into elements, compounds and mixtures:
2. Give any two applications of centrifugation.
4. *State the difference between simple distillation & fractional distillation.
5. * A solution contains 40 ml of ethanol mixed with 100 ml of water. Calculate the
5 Marks Questions:
1. *What is meant by Tyndall effect? What is its cause? Illustrate with example.
2. How would you separate the mixture containing sulphur and sand ?
3. What is crystallization? Give its two applications.
4. How are sol, solution and suspension different from each other?
5. How do we obtain coloured components, i.e. dye from Blue/Black ink ?
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.
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