Thursday, September 8, 2011

CBSE TEST PAPER-IX IS MATTER AROUND US PURE for SA-1

9th Science chemistry Sample paper
Chapter: IS MATTER AROUND US PURE

1. Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?

2. While diluting a solution of salt in water, a student by  mistake added acetone (boiling point 56°C). What technique 
can be employed to get back the acetone? Justify your choice.

3. Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a 
suspension they do.

4. Smoke and fog both are aerosols. In what way are they different?

5. Name the process associated with the following

(a) Dry ice is kept at room temperature and at one atmospheric pressure.

(b) A drop of ink placed on the surface of water contained in a glass spreads throughout the water.

(c) A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.

(d) A acetone bottle is left open and the bottle becomes empty.

(e) Milk is churned to separate cream from it.

(f) Settling of sand when a mixture of sand and water is left undisturbed for some time.

(g) Fine beam of light entering through a small hole in a dark room, illuminates the particles in its paths.

6. The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of 
sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of 
water while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the 
desired solution and why?

7. Why is gold alloyed with copper or silver for the purpose of making ornaments?

8. Give some examples of Tyndall effect observed in your surroundings?

9. Calculate the mass of sodium sulphate required to prepare its 20% (mass percent) solution in 100g of water?

10. How would you separate a mixture of ammonia and hydrogen?

11. Action of heat on blue vitriol is a physical as well as chemical change. Justify.

12. How would you separate a mixture of NH4Cl and I2?

13. Describe a method for separation of the constituents of gunpowder.

14. Describe how you would obtain the substances mentioned below, from the given mixtures.

a) Iodine from tincture of iodine.  b) Lead chloride from a mixture of lead chloride and silver chloride

15. Briefly describe how to separate,

i) Sulphur from a mixture of sulphur and sand.   ii) Black CuO from a mixture of CuO and ZnO.

16. Fill in the blanks

(a) A colloid is a ——— mixture and its components can be separated by  the technique known as ———.

(b) Ice, water and water vapour look different and display different —— properties but they are ——— the same.

(c) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The 
upper layer in the separating funnel will be of——— and the lower layer will be that of ———.

(d) A mixture of two or more miscible liquids, for which the difference in  the boiling points is less than 25 K can be 
separated by the process called———.

(e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the 
——— of light by milk and the phenomenon is called ——— . This indicates that milk is a ——— solution.

Answer: 
1. Crystallization

2. Distillation, since acetone is more volatile it will separate out first.

3. Particle size in a suspension is larger than those in a colloidal solution. Also molecular interaction in a  suspension is not strong enough to keep the particles suspended and hence they settle down.

4. Both fog and smoke have gas as the dispersion medium. The only difference is that the dispersed phase in fog is 
liquid and in smoke it is a solid

5. (a) Sublimation (f) Sedimentation  (b) Diffusion (g) Scattering of light (Tyndall effect) (c) Dissolution/diffusion

(d) Evaporation, diffusion (e) Centrifugation

6. ‘C’ has made the desired solution  

Mass by volume % = Mass of solute/ Volume of solution ×100 = 50×100/100= 50 % mass by volume

7. Pure gold is very soft as compared to gold alloyed with silver or copper. Thus for providing strength to gold, it is 
alloyed

8. Tyndall effect can be seen when light passes through a heterogeneous mixture. Example, when sunlight passes 
through the canopy of a dense forest.

9. Let the mass of sodium sulphate required be = x g  The mass of solution would be = (x +100) g


x g of solute in (x + 100) g of solution

20% = [x/(X+100)] ×100  So ,  x = 25 g

10. Passing the mixture through water can separate the mixture of ammonia and  hydrogen. Ammonia being highly 
soluble dissolves in water while H2 passes out as gas.

11. When blue vitriol is a gradually heated to about 800oC, it undergoes a physical change to form a white powder. 
On adding a drop of water to the white powder, it changes back to blue. Thus the change is a physical change. On 
strongly heating, copper sulphate (blue vitriol) decomposes to give new substances like copper oxide and sulphur 
dioxide. On cooling these, copper sulphate cannot be re-obtained. Thus it is a chemical change.

12. Heating cannot separate the mixture, as both substances sublime on heating. However, when water is added to 
the mixture, NH4Cl dissolves but I2 does not. The mixture is filtered. The filtrate is a solution of NH4Cl, while the 
residue is iodine. The filtrate is heated to obtain NH4Cl crystals.

13. Gunpowder is a mixture of sulphur, charcoal and potassium nitrate (nitre). When water is added to the mixture 
potassium nitrate dissolves. The mixture is then filtered. The filtrate is potassium nitrate solution while the residue is 
a mixture of sulphur and charcoal. The filtrate is evaporated on a sand bath to obtain nitre back. When carbon 
disulphide is added to the residue, sulphur dissolves. When this mixture is filtered the filtrate is sulphur solution while 
the residue is charcoal. Leaving it open evaporates the sulphur solution. Carbon disulphide evaporates and sulphur 
crystals are left behind.

14. a) Iodine dissolved in alcohol is called tincture of iodine. Alcohol is a volatile liquid. So the mixture can be kept 
open or warmed in a water bath. Alcohol will evaporate leaving behind the iodine crystals.

b) Add hot water to the mixture of lead chloride and silver chloride. Lead chloride (PbCl2) is soluble in hot water and 
it dissolves. Silver chloride (AgCl) is insoluble in hot water and so the mixture should be filtered immediately. The 
filtrate is the solution of PbCl2 and the residue is AgCl. The filtrate is heated to obtain crystals of PbCl2.

15. i) Add a solvent to the mixture of sulphur and sand. Sulphur dissolves in carbon disulphide while sand does not. 
When filtered, the residue is sand. The filtrate is kept open, carbon disulphide evaporates and the sulphur crystals 
form.

ii) Add a solvent to the mixture of CuO and ZnO that dissolves only one component e.g. sodium hydroxide. When 
sodium hydroxide is added to the mixture, ZnO dissolves. Filter to obtain the residue of CuO.

16. (a) Heterogeneous, centrifugation  (b) physical, chemically (c) water, chloroform (hint– density of water is less 
than that of chloroform) (d) fractional distillation (e) scattering, Tyndall effect, colloidal

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