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Q.1: Which separation techniques will apply
for the separation of the following?
(a) Sodium chloride from its
solution in water.
(b) Ammonium Chloride from a
mixture containing Sodium Chloride and Ammonium Chloride.
(c) Small pieces of metal in the engine oil
of a car.
(d) Different pigments from an extract of
flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended
in water.
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Ans: (a) Crystallization or Evaporation.
(b) Sublimation.
(c) Centrifugation or Sedimentation.
(d) Chromatography.
(e) Centrifugation.
(f) Separating funnel.
(g) Hand-picking.
(h) Magnetic separation.
(i) Winnowing.
(j) Centrifugation.
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Q.2: Write the steps you would use for
making tea. Use the words - solution, solvent, solute, dissolve, soluble,
insoluble, filtrate and residue.
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Ans: Take the solvent, water, in a kettle.
Heat it. When the solvent boils, add the solute, milk. Milk and waterforms
a solution. Then pour some tea leaves over a sieve. Pour slowly hot solution
of milk over tea leaves. Colour of tea leaves goes into solution as filtrate.
The remaining tea leaves being insoluble remains as residue. Add
requisite sugar which dissolves and the tea is ready.
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Q.3: Explain the
following giving examples:
(a) Saturated solution,
(b) Pure substance, (c) Colloid, (e) Suspension.
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Ans: (a) Saturated Solution -
a solution in which no more of the solid (solute) can be dissolved at a given
temperature is called a saturated solution. Suppose 50 gm of a
solute is the maximum amount that can be dissolved in 100 gm water at 298 K.
Then 150 gm of solution so obtained is the saturated solution at
298 K.
(b) Pure
Substance - A pure substance consists of a single of matter or particles and
can not be separated into other kind of matter by any physical process. Pure
substances always have the same colour, taste and texture at a given
temperature and pressure. For example, pure water is always colorless,
odorless and tasteless and boils at 373 K at normal atmospheric pressure.
(c) Colloid -
Colloids are heterogeneous mixtures the particle size is too small to be seen
with a naked eye, but it is big enough to scatter light. The particles are
called the dispersed phase and the medium in which they are distributed is
called the dispersion medium. Colloids are useful in industry and daily life.
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A colloid has the
following characteristics:
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(1) It is a heterogeneous
mixture.
(2) The size of particles of
a colloid lies between 1 - 100 nm and can not be seen by naked eyes.
(3) The particles of
colloid can scatter a beam of light passing through it and make the path
visible.
(4) The particles of
colloid can not be separated from the mixture by filtration. The process of
separation of colloidal particles is known as ‘centrifugation’.
(5) They do not settle
down when left undisturbed. In other words colloids are quite stable e.g.
smoke, milk, fog, cloud etc.
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(d) Suspension –
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A ‘suspension’ is a heterogeneous
mixture in which the solute particles do not dissolve but remain
suspended throughout the bulk of the medium.
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A suspension has
the following characteristics:
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(1) It is a heterogeneous
mixture.
(2) The size of particles of
a suspension is greater than 100 nm and is visible to naked eyes.
(3) The particles of suspension can
scatter a beam of light passing through it.
(4) The particles of
a suspension settle down when left undisturbed.
(5) The particles of
a suspension can be separated from its mixture by filtration.
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Q.4: Classify each of the
following as a homogeneous or heterogeneous mixture: soda water, wood, air,
soil, vinegar, filtrated tea.
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Ans: Homogeneous
mixture - soda water, air, vinegar, filtered tea.
Heterogeneous
mixture - wood, soil.
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Q.5: How would you
confirm that a colourless liquid given to you is pure water?
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Ans: Every liquid has a
characteristic boiling point at 1 atmospheric pressure. If the given
colourless liquid boils exactly at 373 K at 1 atmospheric pressure, then it
is pure water. If the boiling point is different then the water is
contaminated.
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Q.6: Which of the
following materials fall in the category of a ‘pure substance’?
(a) Ice (b) Milk (c) Iron
(d) Hydrochloric acid (e) Calcium oxide (f) Mercury (g) Brick (h) Wood (i)
Air.
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Ans: (a), (c), (d), (e)
and (f) are pure substances.
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Q.7: Which of the
following will show “Tyndall effect”?
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(a) salt solution (b)
milk (c) copper sulphate solution (d) starch solution.
Ans: (b) and (d) are
colloids and will show Tyndall Effect.
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Q.8: Classify the
following into elements, compounds and mixtures.
(a) sodium
(b) soil
(c) sugar solution (d) silver
(e) calcium carbonate (f)
tin
(g) silicon
(h) coal
(i)
air
(j) soap (k)
methane
(l) carbon dioxide (m) blood
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Ans: Elements -
sodium, silver, tin, silicon.
Compounds - calcium carbonate, methane, carbon
dioxide.
Mixtures -
soil, sugar solution, coal, air, soap, blood.
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Q. 9. In the formation of sodium chloride from
its constituent elements, do the properties of its elements change?
Explain.
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Ans: Sodium is a very reactive metal
that reacts exothermically with water. If we were to ingest a pinch of
sodium, it would burn our intestines. Chlorine is a greenish yellow gas with
a characteristic irritating odour and pungent taste. When sodium and chlorine
combine to form sodium chloride, the properties of the
elements are totally changed. Sodium chloride is a white substance
totally safe to be ingested and is used to add flavour to our food.
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Q. 10. Briefly describe how to
separate, i) Sulphur from a mixture of sulphur and sand. ii) Black CuO from a
mixture of CuO and ZnO.
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Answer:
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.
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Question: 10. Suggest separation
technique(s) one would need to employ to separate the following mixtures.
(a) Mercury and water
Answer: The technique of
Filtration
(b) Potassium chloride and ammonium
chloride
Answer: Sublimation
(c) Common salt, water and sand
Answer: Sedimentation,
decantation, filtration and evaporation
(d) Kerosene oil, water and salt
Answer: First filtration
using separating funnel then after, vapourisation.
Question: 11. Salt can be recovered
from its solution by evaporation. Suggest some other technique for the same?
Answer: To separate salt
from its solution crystallization can also be used.
Question: 12. The ‘sea-water’ can be
classified as a homogeneous as well as heterogeneous mixture. Comment.
Answer: Sea water is the
mixture of many salts, water and other many impurities. Apart from these many
gases are also dissolved in sea water. Because of salt and some other bigger
size of impurities sea water is classified as heterogeneous mixture. Because of
mixture of several gases in sea water it is also classified as homogeneous
mixture.
Question: 13. 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.
Answer: Since, the
boiling point of acetone is 560C and boiling point of water is 1000C,
and for distillation the minimum difference in temperature should be 2500C.
Thus by the process of distillation acetone can be separated.
Question: 14. What would you observe
when
(a) a saturated solution of potassium
chloride prepared at 60°C is allowed to cool to room temperature.
Answer: Since the solution is a
saturated solution, and prepared at 600C which is above the room
temperature, therefore, while it is allowed to cool at room temperature some of
the potassium chloride will settle down at the bottom, because saturation
decreases with decrease in temperature.
(b) an aqueous sugar solution is
heated to dryness.
Answer: When an aquous
solution of sugar is heated to dryness, the sugar will be left behind in the
container after the vaporization of water. The sugar left in the container may
be charred because of more heating.
(c) a mixture of iron filings and
sulphur powder is heated strongly.
Answer: When a mixture
of iron filling and sulphur power is heated strongly ferrous sulphide will be
formed.
Question: 16. Explain why particles of
a colloidal solution do not settle down when left undisturbed, while in the
case of a suspension they do.
Answer: Particles in
colloid is very small compare to that of the suspension. This makes the
colloids more stable than suspension.
Because of the larger size of
particles they settle down when suspension is left undisturbed. While in the
case of colloid they do not settle as the particles are very small.
Question: 17. Smoke and fog both are
aerosols. In what way are they different?
Answer:
Smoke – Smoke is mixture of gases and can goes to higher altitudes because of
having more temperature.
Fog – Fog is mixture of liquid and gases. Fog is settled near the earth
surface because of less temperature.
Question: 18. Classify the following
as physical or chemical properties
(a) The composition of a sample of
steel is: 98% iron, 1.5% carbon and 0.5% other elements.
Answer: This is the
physical property. Since steel is the alloy and considered as mixture of more
than one elements.
(b) Zinc dissolves in hydrochloric
acid with the evolution of hydrogen gas.
Answer: This shows the
reaction of zinc with hydrochloric acid, hence it is a chemical property.
(c) Metallic sodium is soft enough to
be cut with a knife.
Answer: Since, it shows
the softness of sodium, thus is a physical property.
(d) Most metal oxides form alkalis on
interacting with water.
Answer: This property
show the reaction of metal oxides with water, thus a chemical property.
Question: 19. 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?
Answer: Concentration is the relative
percentage of solute compared to the total volume of the solution and it is
calculated by dividing mass by volume.
In the case of A, since 50g of NaOH
has been dissolved in 100 mL of water, the total volume of solution became
about 150 mL, thus concentration of NaOH would be less than 50%.
In the case of B, since 50g of NaOH
has been dissolved in 100g of water, therefore, total volume of the solution
would become 150 mL, consequently concentration of NaOH would again less than
50%.
In the case of C, 50g of NaOH has been
dissolved in water and then volume of the solution made to 100mL, thus
concentration of NaOH would become 50%.
Thus, C made the solution of NaOH
having concentration equal to 50%.
Question: 20. Name the process
associated with the following
(a) Dry ice is kept at room
temperature and at one atmospheric pressure.
Answer: Since, when dry
ice is left at room temperature, it turns into gas, thus this is the process of
sublimation.
(b) A drop of ink placed on the
surface of water contained in a glass spreads throughout the water.
Answer: When a drop of
ink is placed on the surface of water, it spread over the water and finally
mixed with water because of the motion of particles, hence this process is
diffusion.
(c) A potassium permanganate crystal
is in a beaker and water is poured into the beaker with stirring.
Answer: When potassium
permanganate crystals are kept in beaker and water is poured and stirred, the
particles of potassium permanganate would mix with water, because of motion of
particles, stirring speed up the mixing process, hence this is the process of
diffusion.
(d) A acetone bottle is left open and
the bottle becomes empty.
Answer: Since acetone
vaporizes at room temperature, when a acetone bottle is left open the acetone
would vaporize and mix with air, thus this is the process of vaporization.
(e) Milk is churned to separate cream
from it.
Answer: While milk is
churned, the cream and milk is separated because of centrifugal force, thus
this is the process of centrifugation.
(f) Settling of sand when a mixture of
sand and water is left undisturbed for some time.
Answer: When mixture of
sand and water is left undisturbed, the sand settle at the bottom of water,
thus this is the process of sedimentation.
(g) Fine beam of light entering
through a small hole in a dark room, illuminates the particles in its paths.
Answer: When fine beam
of light entered through a small hole in dark room, because of collision of
particles of air and dust, sunbeam illuminates the particles in its path and
dust particles are appeared dancing, this happens because of the Tyndall
effect.
Question: 21. You are given two
samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample
‘B’ boils at 102°C. Which sample of water will not freeze at 0°C? Comment.
Answer: Since impurities
in water raise its boiling point, thus water in sample B is impure. Hence it
will not freeze at 00C because of impurities since impAnswer: Since impurities
in water raise its boiling point, thus water in sample B is impure. Hence it
will not freeze at 00C because of impurities since impurities
decreases the freezing point below the 00C, this is the cause that’s
why sea water remain liquid below the 00C.
Questions for self
assesment
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?
(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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. Which of the following substances
when mixed with sand cannot be separated by sublimation?
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(A) NaCl (B) NH4Cl (C) Camphor (D)
Iodine
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2. Which of the following is a
physical change ?
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(A) Evaporation of alcohol (B) Melting of ice (C) Rusting of iron (D) Both (A) & (B)
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3. What will be the sublimate, when
a mixture of sand, sulphur, common salt and iodine is sublimed?
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(A) Sand (B) Iodine (C) Sulphur (D)
Common salt
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4. Mixture of sand and camphor can
be purified by -
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(A) distillation (B) filtration (C)
sedimentation (D) sublimation
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5. A mixture of alcohol and water
can e separated by
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(A) separating funnel (B)
fractional distillation
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(C) simple distillation (D)
sublimation
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6. To separate the various coloured
pigments present in a substance which method is used?
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(A) sublimation (B) Chromatography
(C) Centrifugation (D) Evaporation
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7. Carbon burns in oxygen to form
carbon dioxide. The properties of carbon dioxide are -
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(A) similar to carbon
(B) similar to
oxygen
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(C) totally different from both
carbon and oxygen
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(D) much similar to both carbon and
oxygen
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8. A mixture of ammonium chloride and sodium chloride can be separated by
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(A) chromatography (B) hand picking
(C) by sublimation (D) centrifugation
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9. Which of the following is not a
chemical change ?
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(A) Rusting of iron (B) Cooking of
food (C) Freezing of water (D) Digestion of food
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10. Which of the following method
is used for separation of different components of petroleum?
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(A) Fractional distillation (B)
Sublimation (C) Chromatography (D) Simple distillation
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Answer:
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10
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A
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D
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B
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D
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B
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B
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C
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C
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C
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A
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