Multiple Choice
(MCQs)
Questsion: 1. Which of the
following statements are true for pure substances?
(i) Pure substances
contain only one kind of particles
(ii) Pure substances may
be compounds or mixtures
(iii) Pure substances have
the same composition throughout
(iv) Pure substances can
be exemplified by all elements other than nickel
(a) (i) and (ii)
(b) (i) and (iii)
(c) (iii) and (iv)
(d) (ii) and (iii)
Answer:
(b) (i) and (iii)
Questsion: 2. Rusting of
an article made up of iron is called
(a) corrosion and it is a
physical as well as chemical change
(b) dissolution and it is
a physical change
(c) corrosion and it is a
chemical change
(d) dissolution and it is
a chemical change
Answer:
(c) Corrosion and it is a chemical change
Questsion: 3. A mixture of
sulphur and carbon disulphide is
(a) heterogeneous and
shows Tyndall effect
(b) homogeneous and shows
Tyndall effect
(c) heterogeneous and does
not show Tyndall effect
(d) homogeneous and does
not show Tyndall effect
Answer:-
(a) Heterogeneous and shows Tyndall effect
Questsion: 4. Tincture of
iodine has antiseptic properties. This solution is made by dissolving
(a) iodine in potassium
iodide
(b) iodine in vaseline
(c) iodine in water
(d) iodine in alcohol
Answer:
(c) Iodine in water
Questsion: 5. Which of the
following are homogeneous in nature?
(i) ice (ii) wood (iii)
soil (iv) air
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (iii) and (iv)
Answer:
(c) (i) and (iv)
Questsion: 6. Which of the
following are physical changes?
(i) Melting of iron metal
(ii) Rusting of iron
(iii) Bending of an iron
rod
(iv) Drawing a wire of
iron metal
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)
Answer:
(c) (i), (iii) and (iv)
Questsion: 7. Which of the
following are chemical changes?
(i) Decaying of wood
(ii) Burning of wood
(iii) Sawing of wood
(iv) Hammering of a nail
into a piece of wood
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer:
(a) (i) and (ii)
Questsion: 8. Two
substances, A and B were made to react to form a third substance, A2B
according to the following reaction :-
2 A + B → A 2 B
Which of the following
statements concerning this reaction are incorrect?
(i) The product A 2 shows the properties of substances A
and B
(ii) The product will
always have a fixed composition
(iii) The product so
formed cannot be classified as a compound
(iv) The product so formed
is an element
(a) (i), (ii) and (iii),
(b) (ii), (iii) and (iv)
(c) (i), (iii) and (iv)
(d) (ii), (iii) and (iv)
Answer:
(c) (i), (iii) and (iv)
Questsion: 9. Two chemical
species X and Y combine together to form a product P which contains both X and
Y X + Y → P
X and Y cannot be broken
down into simpler substances by simple chemical reactions. Which of the
following concerning the species X, Y and P are correct?
(i) P is a compound
(ii) X and Y are compounds
(iii) X and Y are elements
(iv) P has a fixed
composition
(a) (i), (ii) and (iii),
(b) (i), (ii) and (iv)
(c) (ii), (iii) and (iv)
(d) (i), (iii) and (iv)
Answer:
(d) (i), (iii) and (iv)
Short Answer Type
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. Which of the
tubes in Figure given here (a) and (b) will be more effective as a condenser in
the distillation apparatus?
Answer:
Figure (a) will be more effective, because of containing fractionating column.
Question: 12. 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: 13. 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: 14. 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: 15. 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.
Short Answer Type
- part - 2
Question: 22. What are the
favourable qualities given to gold when it is alloyed with copper or silver for
the purpose of making ornaments? ed with copper or silver for making of
ornaments.
Answer:
Since, Gold is a highly malleable metal so it is difficult to make the
ornaments with pure gold, thus to make its rigidity desiring gold is alloyed
with copper or silver for making of ornaments.
Question: 23. An element
is sonorous and highly ductile. Under which category would you classify this
element? What other characteristics do you expect the element to possess?
Answer:
Since a metal is sonorous and ductile, thus if an element possesses these
qualities this will be kept under the category of metals. The other qualities
of metal are good conductor of heat and electricity, lustrous, malleability,
etc.
Question: 24. Give an
example each for the mixture having the following characteristics. Suggest a
suitable method to separate the components of these mixtures
(a) A volatile and a
non-volatile component.
Answer:
The mixture of acetone and water. In this acetone is volatile and water is
non-volatile. The mixture of water and acetone can be separated by the process
of distillation.
(b) Two volatile
components with appreciable difference in boiling points.
Answer:
Mixture of acetone and ethanol. The boiling point of acetone is 560C and that
of ethyl alcohol is 78.40C.
The
mixture of acetone and ethanol can Answer: Mixture of acetone and ethanol. The
boiling point of acetone is 560C and that of ethyl alcohol is 78.40C.
The
mixture of acetone and ethanol can be separated using fractional distillation.
er are two immiscible liquids, thus their mixture can be separated using
separating funnel.
(d) One of the components
changes directly from solid to gaseous state.
Answer:
The mixture of salt and ammonium chloride. In this mixture ammonium chloride
changes from solid to gaseous state directly.
The
mixture of salt and ammonium chloride can be separated by the process of
sublimation.
(e) Two or more coloured
constituents soluble in some solvent.
Answer:
The ink is the mixture of dyes of many colours.
The
different dyes of ink can be separated using chromatography.
Question: 25. Fill in the
blanks
(a) A colloid is a
__________ mixture and its components can be separated by the technique known
as _________.
Answer: heterogeneous,
centrifugation
(b) Ice, water and water
vapour look different and display different _________ properties but they are
___________ the same.
Answer: Physical,
chemically
(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 ___________.
Answer:
chloroform, water
(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____________.
Answer:
Fractional distillation
(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:
scattering, Tyndall Effect, colloidal
Question: 26. Sucrose
(sugar) crystals obtained from sugarcane and beetroot are mixed together. Will
it be a pure substance or a mixture? Give reasons for the same.
Answer:
Pure substance, since it contains a single component, i.e. sucrose.
Question: 27. Give some
examples of Tyndall effect observed in your surroundings?
Answer:
Examples of Tyndall Effect:
Sunbeam
coming from ventilation. The dust particles present in the way of beam looks
luminous because of the scattering of light.
Milk in a
glass appearing faint blue, since milk is a colloid and light passes through it
scattered.
Sunbeam
coming from behind the clouds looks luminous because of the scattering of
light.
Question: 28. Can we
separate alcohol dissolved in water by using a separating funnel? If yes, then
describe the procedure. If not, explain.
Answer:
The mixture of alcohol and water cannot be separated using a separating funnel,
since these are not immiscible liquids.
The
mixture of alcohol and water can be separated by the process of distillation.
Question: 29. On heating
calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or
a chemical change?
Answer:
The conversion of calcium carbonate into calcium oxide and carbon dioxide is a
chemical change.
(b) Can you prepare one
acidic and one basic solution by using the products formed in the above
process? If so, write the chemical equation involved.
Answer:
Yes one acidic and one basic solution can be formed by the calcium oxide and
carbon dioxide, which are product formed in the above process.
Since
metallic oxides are basic and non-metallic oxides are acidic in nature.
Calcium
oxide is a metallic oxide. Hence by dissolving it in water a basic solution is
formed because of the formation of calcium hydroxide. The reaction
involvedCalcium oxide is a metallic oxide. Hence by dissolving it in water a
basic solution is formed because of the formation of calcium hydroxide. The
reaction involved in this can be written as follows:
CaO + H2O
⇌ Ca(OH)2
Carbon is
a non metal hence carbon dioxide is acidic in nature. When it is dissolved in
water an acidic solution is formed.
CO2+H2O⇌H2CO3
Question: 30. 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.
Answer:
Graphite
(b) Name a non-metal which
exists as a liquid at room temperature.
Answer:
Bromine
(c) The allotropic form of
a non-metal is a good conductor of electricity. Name the allotrope.
Answer:
Graphite. Graphite is a good conductor of electricity. It is an allotropic form
of carbon.
(d) Name a non-metal which
is known to form the largest number of compounds.
Answer:
Carbon is a non-metal. It is known to form the largest number of compounds.
(e) Name a non-metal other
than carbon which shows allotropy.
Answer:
Sulphur is a non-metal which shows allotropy. Disulphur and trisulphur are some
of the allotropes of sulphur.
(f) Name a non-metal which
is required for combustion.
Answer:
Oxygen
Question: 31. Classify the
substances given in Figure into elements and compounds
Answer:
Elements: Cu,
Zn, O2, F2, Hg, Diamond
Compound: CaCO3,
NaCl(aq), H2O,
Question: 32. Which of the
following are not compounds?
(a) Chlorine gas
(b) Potassium chloride
(c) Iron
(d) Iron sulphide
(e) Aluminium
(f) Iodine
(g) Carbon
(h) Carbon monoxide
(i) Sulphur powder
Answer:
Chlorine gas, iron, aluminium, iodine, carbon and sulphur powder are not
compounds.
Long Answer Type
Questions - part - 1
33. Fractional
distillation is suitable for separation of miscible liquids with a boiling
point difference of about 25 K or less. What part of fractional distillation
apparatus makes it efficient and possess an advantage over a simple
distillation process. Explain using a diagram.
Answer:
Ref: NCERT Book
Apparatus
used for fractional distillation has a fractionating column. A simple
fractionating column has glass beads in it which provide additional surface
area because of which the vapours can spread and cool rapidly. Hence,
fractionating column is used to provide the additional surface and to
facilitate the cooling of vapour in many cycles.
34. (a) Under which
category of mixtures will you classify alloys and why?
Answer:
When
constituent particles of a combination of two or more element or compound
retains their properties, then it is called mixture. In an alloy the
constituent particles, hence alloys are classified as mixture. For example;
steel is an alloy of carbon and iron.
(b) A solution is always a
liquid. Comment.
Answer:
Since, a solution is the homogeneous mixture of two or more substances, thus it
is not necessary that a solution would always a liquid.
A
solution can be in all the three states of matter. A solution is a homogeneous
mixture and can be in all the three states of matter.
Example:
Solution
of alcohol in water is a liquid.
Air is a
solution of different gas.
Alloy is a solution which
is in the form of solid.
(c) Can a solution be
heterogeneous?
Answer:
Solution is defined as the homogeneous mixture, hence a solution cannot be
heterogeneous. But when a mixture becomes heterogeneous, it cannot be fall
under the definition of solution.
35. Iron filings and
sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’
was heated strongly while Part ‘B’ was not heated. Dilute hydrochloric acid was
added to both the Parts and evolution of gas was seen in both the cases. How will
you identify the gases evolved?
Answer:
Hydrogen
gas is released, when dilute hydrochloric acid is added to part ‘A’. Hydrogen
gas can be tested by brining a burning matchstick or candle near it. When a
burning matchstick is placed near the hydrogen gas, it burns with a pop sound,
which is a test for hydrogen gas.
Hydrogen
sulphide gas released when dilute hydrochloric acid was added to part ‘B’.
Hydrgoen sulphide gas smells like a rotten egg, hence it could be confirmed by
its smell.
36. A child wanted to
separate the mixture of dyes constituting a sample of in36. A child wanted to
separate the mixture of dyes constituting a sample of ink. He marked a line by
the ink on the filter paper and placed the filter paper in a glass containing
water as shown in Fig. The filter paper was removed when the water moved near
the top of the filter paper.
(i) What would you expect
to see, if the ink contains three different coloured components?
Answer:
Streaks of different colours can be seen on the filter paper.
(ii) Name the technique
used by the child.
Answer:
Chromatography
(iii) Suggest one more
application of this technique.
Answer:
Chromatography is used for separating pigments from colours, for the separation
drugs from blood sample, etc.
Long Answer Type
Questions - part - 2
37. A group of students
took an old shoe box and covered it with a black paper from all sides. They
fixed a source of light (a torch) at one end of the box by making a hole in it
and made another hole on the other side to view the lig37. A group of students
took an old shoe box and covered it with a black paper from all sides. They
fixed a source of light (a torch) at one end of the box by making a hole in it
and made another hole on the other side to view the light. They placed a milk
sample contained in a beaker/tumbler in the box as shown in the Fig. They were
amazed to see that milk taken in the tumbler was Fig.illuminated. They tried
the same activity by taking a salt solution but found that light simply passed
through it?
(a) Explain why the milk
sample was illuminated. Name the phenomenon involved.
Answer:
Since, milk is a colloid and when light scattered from the particles of
colloids, it is illuminated, thus light was illuminated when passed through the
milk. This is known as Tyndall Effect.
(b) Same results were not
observed with a salt solution. Explain.
Answer:
For scattering of light the size of particles should be large enough. Since the
particles of solution are not enough to scattered the beam of light, hence same
result were not observed.
(c) Can you suggest two
more solutions which would show the same effect as shown by the milk solution?
Answer:
Soap bubbles and fog are the colloids, hence same effect, i.e. scattering of
light is shown by these. This is known as Tyndall effect.
38. Classify each of the
following, as a physical or a chemical change. Give reasons.
(a) Drying of a shirt in
the sun.
Answer:
Drying of shirt in the sun is a Physical change. Since in this change no new
substance is formed.
(b) Rising of hot air over
a radiator.
Answer:
Since, in rising of hot air over a radiator no new substance is formed, hence
it is a Physical change.
(c) Burning of kerosene in
a lantern.
Answer:
While burning of kerosene in a lantern carbon dioxide, and water vapour is
formed, hence it is a Chemical change.
(d) Change in the colour
of black tea on adding lemon juice to it.
Answer:
In this change a new substance is formed, hence it is a Chemical change.
(e) Churning of milk cream
to get butter.
Answer:
While churning of milk cream to get butter, no new substance is formed, hence
it is a Physical change.
39. During an experiment
the students were asked to prepare a 10% (Mass/Mass) solution of sugar in
water. Ramesh dissolved 10g of sugar in 100g of water while Sarika prepared it
by dissolving 10g of sugar in water to make 100g of the solution.
(a) Are the two solutions
of the same concentration
Answer:
No, the two solutions have different concentrations.
(b) Compare the mass % of
the two solutions.
Answer:
We know;
For first
solution:
Mass of
solute = 10 gram
Mass of
solution = 100 gram + 10 gram = 110 gram
Hence;
For
second solution:
Mass of
solute = 10 gram
Mass of
solution = 100 gram
Hence;
Mass
percent of first solution: Mass percent of second solution = 9.99: 10
40. You are provided with
a mixture containing sand, iron filings, ammonium chloride and sodium chloride.
Describe the procedures you would use to separate these constituents from the
mixture?
Answer:
The given mixture can be separated using the following process.
Magnetic
Separation: Using
magnetic separation the iron fillings can be separated from the given mixture.
In this a
magnet is hover just above the mixture, since iron is a magnetic substance it
is attracted by magnet and stuck with it. By this first of all iron fillings
are separated.
Sublimation: After
the separation of iron fillings, ammonium chloride is separated by the process
of sublimation.
Since,
ammonium chloride is a sublimate and it turns into vapour directly without
changing into liquid, thus when the mixture is sublimated, the ammonium
chloride is deposited over the inner wall of funnel leaving the sodium chloride
and sand in the watch glass. Ammonium chloride is separated by scratching from
the inner wall of the funnel.
Filtration: Now
the left mixture of sand and sodium chloride is put in water, after stirring
the sodium chloride is dissolved in water. The solution is separated by the
process of filtration. The sand left over the filter paper is separated out.
Vapourisation: By
the process vaporization, the liquid so obtained is vapouried and crystals of
ammonium chloride can be obtained.
Hence, by
using the methods of magnetic separation, sublimation, filteration and
vapourisation and crystallization the component of given mixture of sand, iron
fillings, ammonium chloride and sodium chloride can be separated.
41. Arun has prepared
0.01% (by mass) solution of sodium chloride in water. Which of the following
correctly represents the composition of the solutions?
(a) 1.00 g of NaCl + 100g
of water
(b) 0.11g of NaCl + 100g
of water
(c) 0.0l g of NaCl +
99.99g of water
(d) 0.10 g of NaCl +
99.90g of water
Answer:
(c) 0.01 g of NaCl + 99.99 g of water
42. Calculate the mass of
sodium sulphate required to prepare its 20% (mass percent) solution in 100g of
water?
Answer:
In a 20% solution containing 100 g water; the mass percentage of water = 100 –
20 = 80%
Hence; to
prepare 20% (w/w) solution in 100 gram of water 25 gram of sodium sulphate is
needed.
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