NCERT solution of class 9 chapter IS matter around us pure
Page no. 15
Question 1:
What is meant by a pure substance?
Answer 1:
A pure substance is the
one that consists of a single type of particles, i.e., all constituent
particles of the substance have the same chemical nature. Pure substances can
be classified as elements or compounds.
Question 2:
List the points of
differences between homogeneous and heterogeneous mixtures.
Answer 2:
A homogeneous mixture is a
mixture having a uniform composition throughout the mixture. For example: salt
in water, sugar in water, copper sulphate in water
A heterogeneous mixture is
a mixture having a non-uniform composition throughout the mixture. For example:
sodium chloride and iron fillings, salt and sulphur, oil and water
Page no.18
Question 1:
Differentiate between
homogeneous and heterogeneous mixtures with examples.
Answer 1:
A homogeneous mixture is a
mixture having a uniform composition throughout the mixture. For example,
mixtures of salt in water, sugar in water, copper sulphate in water, iodine in
alcohol, alloy, and air have uniform compositions throughout the mixtures.
On the other hand, a
heterogeneous mixture is a mixture having a non-uniform composition throughout
the mixture. For example, composition of mixtures of sodium chloride and iron
fillings, salt and sulphur, oil and water, chalk powder in water, wheat flour
in water, milk and water are not uniform throughout the mixtures.
Question 2:
How are sol, solution and
suspension different from each other?
Answer 2:
Sol is a heterogeneous
mixture. In this mixture, the solute particles are so small that they cannot be
seen with the naked eye. Also, they seem to be spread uniformly throughout the
mixture. The Tyndall effect is observed in this mixture. For example: milk
of magnesia, mud
Solution is a homogeneous
mixture. In this mixture, the solute particles dissolve and spread uniformly
throughout the mixture. The Tyndall effect is not observed in this mixture.
For example: salt in
water, sugar in water, iodine in alcohol, alloy
Suspensions are
heterogeneous mixtures. In this mixture, the solute particles are visible to
the naked eye, and remain suspended throughout the bulk of the
medium. The Tyndall effect is observed in this mixture.
For example: chalk
powder and water, wheat flour and water
Question 3:
To make a saturated
solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find
its concentration at this temperature.
Answer 3:
Page no. 24.1
Question 1:
How will you separate a
mixture containing kerosene and petrol (difference in their boiling points is
more than 25°C), which are miscible with each other?
Answer 1:
A mixture of two miscible
liquids having a difference in their boiling points more than 25°C can be
separated by the method of distillation. Thus, kerosene and petrol can be
separated by distillation
In this method, the
mixture of kerosene and petrol is taken in a distillation flask with a
thermometer fitted in it. We also need a beaker, a water condenser, and a
Bunsen burner. The apparatus is arranged as shown in the above figure. Then,
the mixture is heated slowly. The thermometer should be watched simultaneously.
Kerosene will vaporize and condense in the water condenser. The condensed
kerosene is collected from the condenser outlet, whereas petrol is left behind
in the distillation flask.
Question 2:
Name the technique to
separate
(i) butter from curd
(ii) salt from sea-water
(iii) camphor from salt.
Answer 2:
(i) Butter can be separated from curd by centrifugation.
(ii) Salt can be separated from sea-water by evaporation.
(iii) Camphor can be separated from salt by sublimation.
Question 3:
What type of mixtures is
separated by the technique of crystallization?
Answer 3:
By the technique of
crystallization, pure solids are separated from impurities. For example, salt
obtained from sea is separated from impurities; crystals of alum (Phitkari)
are separated from impure samples.
Page no.24.2
Question 1:
Classify the following as
chemical or physical changes:
• cutting of trees,
• melting of butter in a
pan,
• rusting of almirah,
• boiling of water to form
steam,
• passing of electric
current, through water and the water breaking down into hydrogen and oxygen
gases,
• dissolving common salt
in water,
• making a fruit salad
with raw fruits, and
• burning of paper and
wood.
Answer 1:
Cutting of trees → Physical change
Melting of butter in a pan → Physical change
Rusting of almirah → Chemical change
Boiling of water to form steam → Physical change
Passing of electric current through water, and water
breaking down into hydrogen and oxygen gas → Chemical change
Dissolving common salt in water → Physical change
Making a fruit salad with raw fruits → Physical change
Burning of paper and wood → Chemical change
Question 2:
Try segregating the things
around you as pure substances or mixtures.
Answer 2:
Pure substance: Water,
salt, sugar etc.
Mixture: Salt water, soil,
wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food.
Exercises
Question 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.
Answer 1:
(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.
Question 2 Write the steps you would use for making tea. Use the
words - solution, solvent, solute, dissolve, soluble, insoluble, filtrate and
residue.
Answer 2:
Take the solvent, water,
in a kettle. Heat it. When the solvent boils, add the solute, milk. Milk and
water forms 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.
Question4:
Explain the following
giving examples.
(a) Saturated solution,
(b) Pure substance,
(c) Colloid,
(d) Suspension.
Answer 4: (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 cannot 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
colourless, 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. A colloid has the following characteristics:
It is a heterogeneous
mixture.
The size of particles of a
colloid lies between 1 - 100 nm and cannot be seen by naked eyes.
The particles of colloid
can scatter a beam of light passing through it and make the path visible.
The particles of colloid
cannot be separated from the mixture by filtration. The process of separation
of colloidal particles is known as ‘centrifugation’.
They do not settle down
when left undisturbed. In other words colloids are quite stable e.g. smoke,
milk, fog, cloud etc.
(d) Suspension: A ‘suspension’ is a heterogeneous mixture
in which the solute particles do not dissolve but remain suspended throughout
the bulk of the medium. A suspension has the following characteristics:
It is a heterogeneous
mixture.
The size of particles of a
suspension is greater than 100 nm and is visible to naked eyes.
The particles of
suspension can scatter a beam of light passing through it.
The particles of a suspension
settle down when left undisturbed.
The particles of a
suspension can be separated from its mixture by filtration.
Question 5:
Classify each of the
following as a homogeneous or heterogeneous mixture: soda water, wood, air,
soil, vinegar, filtrated tea.
Answer 5:
Homogeneous mixture - soda
water, air, vinegar, filtered tea.
Heterogeneous mixture -
wood, soil.
Question 6: How would you confirm that a colourless liquid given
to you is pure water?
Answer 6: 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.
Question 7: 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.
Answer 7: (a), (c), (d), (e) and (f) are pure substances.
Question 8 Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water.
Answer 8 Solutions among the following mixtures.
(b) Sea water
(c) Air
(e) Soda water.
Question 9: Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution.
Answer 9: (b) and (d) are colloids and will show Tyndall
Effect.
Question 10: 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
Answer 10:
Elements - sodium, silver,
tin, silicon.
Compounds - calcium
carbonate, methane, carbon dioxide.
Mixtures - soil, sugar
solution, coal, air, soap, blood.
Question 11 Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle.
Answer 11:
Following are Chemical
changes.
(a) Growth of a plant
(b) Rusting of iron
(c) Cooking of food
(d) Digestion of food
(e) Burning of a candle.
