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IS MATTER AROUND US PURE
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| 2012-08-18, 9:37 AM |
9th
CBSE TEST PAPER 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.
ANSWERS
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, NH4
Cl dissolves but I2
does not. The mixture is filtered. The
filtrate is a solution of NH
4Cl, while the residue is iodine. The filtrate is heated to obtain NH4
Cl
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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