Given below are the Class 9 Science CBSE Important questions Is Matter around us pure
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Very Short Answers questions
Question 1. State any one difference between pure and impure substances.
Solution
The constituents, which make up a pure substance cannot be separated by physical means
The constituents of an impure substance can be separated by physical means.
Question 2. What is meant by concentration of a solution?
Solution
The concentration of a solution is the amount of solute present per unit volume or per unit massof the solution or solvent.
Question 3. List the two conditions essential for using distillation as a method for separation of the components from a mixture.
Solution
1. two liquids must be miscible that is they totally mix with each other.
2. the difference between the boiling points of the liquids should be less than 25k.
Question 4. Smoke and fog both are aerosols. In what way are they different?
Solution
They differ by their composition. They both are colloidal mixtures but smoke is consists of air mixed with carbon particles but fog consists of air mixed with water vapour ( mostly).
Question 5. What do you understand by the statement 'the solubility of NaCl is 36.5 g at room temperature'?
Solution
It means that, at room temperature 36.5 g of Nacl can be dissolved in 100 g (or 100 ml) of water.
Question 6. Salt can be recovered from its solution by evaporation. Can you suggest any other technique also?
Solution
Crystallisation method.
Question 7. Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. Of not, explain.
Solution
No, being miscible they cannot be separated by using a separating funnel.
Question 8. Crystallization is a better technique than sample evaporation. Give one reason to justify the statement.
Solution
Crystallization is better than evaporation in mainly two ways :
1. In evaporation, the solution needs to be at the boiling point of the solvent, the whole time. This may degrade the solute.
2. In crystallization, the crystals automatically throw away impurities to arrange themselves in a regular manner. Therefore, the degree of purity is higher than the solute left after evaporation.
Question 9. Define an element.
Solution
Element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Short Answers questions
Question 1. A solution is prepared by adding 40 g of sugar in 100 g of water. Calculate the concentration in terms of mass by mass percentage of solution.
Solution
Given,
mass of sugar= 40g
mass of water= 100g
To find :- concentration of sugar in water
Total mass of solution = mass of sugar + mass of water=100g +40g = 140g
percentage of concentration of sugar in solution=
$\frac {40}{140} \times 100 =28.57% $approx
Question 2. How Tyndall effect can be observed in the canopy of a dense forest.
Solution
Tyndall effect refers to the process by which light is scattered by colloids or suspension making the path of the light to be visible.
In the forests, the air contains mists which acts as the colloids hence when light seeps in through the canopy one clear sees its path.
Question 3. How do solultion and gel differ from each other? Give one example for each.
Question 4. What volume of ethyl alcohol and water must be mixed together to prepare 250 ml of 60% by volume of alcohol in water.
Solution
60% by volume of alcohol solution means, each 100 ml of solution will have 60 ml ethyl alcohol
So, 250 ml of solution will have = (60 /100) x250 = 150 ml of ethyl alcohol
Hence, In a 250 ml solution of 60% by volume of alcohol and water, alcohol should be 150 ml and water should be 100ml
Question 5. 'Sea water can be classified as homogeneous as well as heterogeneous mixture.' Comment.
Question 6. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Question 7. Non-metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
a.Name a lustrous non-metal.
b.Name a non-metal which exists as a liquid at room temperature.
c.The allotropic form of a non – metal is a good conductor of electricity. Name the allotrope.
d.Name a non-metal which is known to form the largest number of compounds.
e.Name a non-metal other than carbon which shows allotrophy.
f.Name a non-metal which is required for combustion.
Solution
(a) Iodine is a lustrous non-metal.
(b) Bromine is a non-metal which exists as a liquid at room temperature.
(c) Graphite is the allotropic form of carbon and it is a good conductor of electricity.
(d) Carbon is a non-metal which is known to form the largest number of compounds.
(e) Phosphorus is a non-metal other than carbon which shows allotropy.
(f) Oxygen is a non-metal which is required for combustion.
Question 8. A solution contains 50 g of sugar in 350 g of water. Calculate the concentration of solution in terms of mass by mass percent of the solution.
Solution
ass of solute = 50g
mass of solvent = 350g
mass of solution = 50 + 350 = 400g
$\text {mass by mass%} = \frac {\text{mass of solute}}{\text{mass of solution}} \times 100 $
$\text{mass by mass %} = \frac {50}{400} \times 100$
= 12.5%
Question 9. Mention in tabular form any two differences between heterogeneous and homogeneous mixtures.
Question 10. What is tincture of iodine? Identify the solute and solvent in it.
Solution
Tincture of iodine means the solution of iodine and alcohol.The solute is iodine and solvent is alcohol.
Question 11. What are aerosols? Give any two examples.
Question 12. What is meant by an aqueous and non-aqueous solutions? Give one example of each.
Question 13. What is a solution? Write two examples.
Question 14. When is a solution said to be saturated? How can you change an unsaturated solution to a saturated solution without adding any more solvent to it?
Question 15. Smoke and fog are aerosols. How do they differ from each other?
Question 16. What is Tyndall effect? Why the solution of copper sulphate does not show Tyndall effect?
Solution
Tyndall effect refers to the process by which light is scattered by colloids or suspension making the path of the light to be visible
Copper sulphate when dissolves in water forms a true solution. True solution does not show tyndall effect.
Question 17. To make a saturated solution, 72 g of sodium chloride is dissolved in 200 g of water at 20
0C. find its concentration at the same temperature.
Solution
Concentration is given by = $ \frac {\text{Mass of solute}{\text{Mass of solution}} \times 100$
mass of solute= 72g
mass of solution= 72g + 200g
$Concentration= \frac {72}{272} \times 100 = 26.47%$
Question 18. You are provided with solution of substance ‘X’. how will you test whether it is saturated or unsaturated with respect to ‘X’ at a given temperature? What happens when a hot saturated solution is allowed to cool?
Question 19. Name the appropriate methods to separate the following:
a.Nitrogen from air
b.Dye from blue ink
c.Butter cream from milk
d.Ammonium chloride from common salt
Solution
a. Fractional distillation
b. Process of evaporation
c. Process of centrifugation
d. sublimation
Question 20. What is chromatography? Mention its two applications.
Solution
Chromatography is a method used to separate mixture that comprises solutes that dissolve in the same solvent.This method gets its name from the Greek word for colour -Kroma, as it was first used for separating colours.
Principle: Chromatography is based on differential affinities of compounds towards two phases, i.e stationary and mobile phase.
The fraction with greater affinity towards stationary phase travels shorter distance while the fraction with less affinity towards stationary phase travels longer distance.
Chromatography is used for separating colors in a dye, pigments from natural colors and drugs from blood.
Question 21. Draw a flow diagram showing the process of obtaining gases from air.
Solution
Question 22.State the separation technique used for the separation of the following:
a.Ammonium chloride from a mixture containing sodium chloride and ammonium chloride
b.Copper sulphate from its solution in water.
Solution
a. Sublimation
b. Crystallisation
Question 23. Classify the following into physical or chemical change:
(i) Burning of a candle
(ii) Freezing of water
(iii) Mixing of iron filings and sand
(iv) Fading of clothes
Solution
i. Physical and chemical change both
ii. Physical change
iii. Physical change
iv. Chemical change
Question 24. What are metalloids? Give two examples.
Solution
Metalloid, a chemical element with properties intermediate between those of typical metals and nonmetals. Usually considered under this classification are the chemical elements boron, silicon, germanium, arsenic, antimony, and tellurium
Question 25. Classify the following as metals, non-metals and metalloids:
Copper, silicon, carbon, chlorine, gold, boron.two non – metals from the following elements:
Solution
Copper,Gold :Metal
Silicon,Boron: Metalloids
Carbon,Chlorine: Non metals
Question 26. (a) Identify two non – metals from the following elements:
Carbon, Sodium, Chlorine, Neon, Platinum
(b) Name the appropriate method to separate nitrogen from air.
(c) Identify dispersed phase and dispersion medium in foam and rubber.
Solution
a.Carbon,Chlorine: Non metals
b.Fractional distillation
c. Dispersion phase is Gas and dispersion medium is solid
Question 27. Identify the numbers
Solution
1. elements
2. Compounds
3. homogenous
3. hetrogenous
Question 28. Classify the substances given in below figure into elements and compounds
Solution
Elements: $N_2$,$H_2$,$CL_2$,Diamond
Compounds: $H_20$,$CuSO_4$,Carbon dioxide,$HCL$, Methane,Calcium Carbonate
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