Is Matter Around Us Pure
Science Class Ninth
NCERT IN TEXT Solution
Question: 1. What is meant by a substance?
Answer: Anything which has mass and volume are called substance. Substance can be classified into two types: Pure substance and Impure substance.
Pure substance: Substances which cannot be broken down into their constituent particles by simple physical methods are called Pure substances. For example: iron, gold, water, silver, oxygen, etc.
Elements and compounds are pure substances.
Impure substance: All mixtures are impure substances. And they can be broken down into their constituents by simple physical processes. For example: air, salt solution in water, sugar solution in water, etc.
Question: 2. List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
| Difference between Homogeneous and Heterogeneous mixtures | |||
|---|---|---|---|
| Homogeneous Mixture | Heterogeneous Mixture | ||
| Have uniform composition throughout. | Do not have uniform composition throughout. | ||
| Stable | Unstable, but colloids are stable | ||
| Size of particles are very small | Size of particles are larger than homogeneous mixture | ||
| Do not scatter path of visible light | Scatter path of visible light | ||
Question: 3. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:
| Difference between Homogeneous and Heterogeneous mixtures | |||
|---|---|---|---|
| Homogeneous Mixture | Heterogeneous Mixture | ||
| Have uniform composition throughout. | Do not have uniform composition throughout. | ||
| Stable | Unstable, but colloids are stable | ||
| Size of particles are very small | Size of particles are larger than homogeneous mixture | ||
| Do not scatter path of visible light | Scatter path of visible light | ||
| Example: solution of sugar in water, salt solution in water, solution of alcohol and water, Air, alloys, bronze | Example: Shaving cream, gel, smoke, fog, foam, milk, etc. | ||
Question: 4. How are sol, solution and suspension different from each other?
Answer:
| Difference among Sol, Solution and Suspension | |||
|---|---|---|---|
| Sol | Solution | Suspension | |
| Heterogeneous mixture | Homogeneous mixture | Heterogeneous mixture | |
| Stable | Stable | Unstable | |
| Scatter beam of visible light | Do not scatter beam of visible light | Scatter beam of visible light | |
| Particles of smaller than suspension | Particles are smallest compare to sol and suspension | Particles are larger than sol and solution | |
Question: 5. To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
Answer:
Solution:
Given, Mass of solute (sodium chloride) = 36 g
Mass of solvent (water) = 100 g
We know that Mass of solution = Mass of solute + Mass of solvent
Thus, mass of the given solution = 36 g + 100 g = 136 g
And we know that,
Mass by mass percentage of a solution `=(text{Mass of solute})/(text{Mass of solution})xx100`
Thus, Mass percentage of the given solution
`=(36\ g)/(136\ g) xx100`
`=9/34 xx 100 = 26.47%`
Thus, concentration of the given solution = 26.47% Answe
Question: 6. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25oC), which are miscible with each other?
Answer:
Since, the difference in boiling points of kerosene and petrol is more than 25oC, thus mixture of these miscible liquids can be separated by the method of distillation.
Process:
Mixture is taken in the distillation flask.
A condenser and a thermometer are fitted with distillation flask.
A container to collect petrol is fitted with condenser.
After started heating, the petrol which has lower boiling point, starts converting into gas first.
Petrol is get collected into the container after getting condensed.
Gradually all petrol is collected in container leaving kerosene in the distillation flask.
Thus, using this method of distillation, both the liquid is got separated.
Question: 7. Name the technique to separate
(i) Butter from curd.
Answer: Centrifugation.
Explanation: Since butter is dispersed in the curd. And particles of butter is not enough large to get filtered.
Thus, by using the method of centrifugation, butter being denser gets collected at the bottom, which is drained out.
(ii) Salt from sea water
Answer: Evaporation.
Explantion: Salt is gets dissolved in sea water. Thus by the method of evaporation, sea water gets evaporated leaving salt behind it.
(iii) Camphor from salt.
Answer: Sublimation.
Explanation: Camphor goes under sublimation as it converts into gas without changing into liquid and from gas into solid without changing into liquid.
Thus by applying method of sublimation, the mixture of salt and camphor is separated.
Question: 8. What type of mixtures are separated by the technique of crystallization?
Answer: Using the method of crystallistion, crystals of pure substance can be obtained from the mixture of impure sample.
Question: 9. Classify the following as chemical or physical changes:
Cutting of trees.
Answer: Physical change.
Explanation: As in cutting of tree no new substance is formed, thus cutting of tree is a physical change.
Melting of butter in a pan
Answer: Physical change.
Explanation: After melting of butter in a pan only physical state of butter is changed, i.e. butter changes from solid into liquid , and no new substance is formed. Thus melting of butter in a pan is a physical change.
Rusting of almirah
Answer: Chemical change.
Explanation: Since, by rusting of almirah, a new substance rust (iron oxide) is form after the reaction of iron of almirah with moisture present in atmosphere. Thus Rusting of almirah is a chemical change.
Boling of water to form steam
Answer: Physical change
Explanation : After boiling only physical state of water (liquid) is changed into steam (vapour) and no new substance is formed . Thus, boiling of water to form steam is a physical change.
Passing of electric current, through water and the water breaking down into hydrogen and oxygen gases.
Answer: Chemical change.
Explanation: By passing of electric current into water, water breaks down into hydrogen and oxygen. Thus, here new substances are formed. Thus, Passing of electric current, through water and the water breaking down into hydrogen and oxygen gases is a chemical change.
Dissolving common salt in water.
Answer: Physical change.
Explanation: After dissolving of salt in water, no new substance is formed. And salt can be obtained easily using simple physical methods, i.e. evaporation. Thus, dissolving common salt in water is a physical change.
Making a fruit salad with raw fruits and
Answer : Physical change
Explanation : As after making of fruit salad with raw fruit, no new substance is formed in addition to this no chemical reaction takes place, thus making of fruit salad with raw fruit is a physical change.
Burning of paper and wood
Answer : Chemical change.
Explanation : In burning of anything new substances are formed, thus burning of anything is a chemical change.
Consequently, burning of paper and wood are chemical changes.
Question: 10. Try segregating the things around you as pure substances or mixtures.
Answer :
Pure substance: Water, coal, silver, gold, copper, iron, etc.
Mixture: air, tea juice, cold drink, milk, stainless steel, etc.
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