EVENTS CONVENT HIGH SCHOOL
12/01/2021 cLASS-9 SLOT-2
SCIENCE
Chapter-2 IS MATTER AROUND US PURE?
_________________________________________________________________
Answer: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: 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
Question 3:How are sol, solution and suspension
different from each other?
Answer: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 4: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:Mass of solute (sodium chloride) = 36 g (Given)
Mass of solvent
(water) = 100 g (Given)
Then, mass of
solution = Mass of solute + Mass of solvent
= (36 + 100) g
= 136 g
Therefore,
concentration (mass by mass percentage) of the solution
Question 5: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: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.
Question 6:Classify the following as chemical
or physical changes:
Answer:• 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 7:Name the technique to separate
(i) butter from
curd
(ii) salt from
sea-water
(iii) camphor
from salt
Answer:
(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 8:Try segregating the things around
you as pure substances or mixtures.
Answer:Pure substance: Water, salt, sugar
Mixture: Saltwater,
soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food
Question 9:What type of mixtures is separated
by the technique of crystallization?
Answer:By the technique of crystallization, pure solids
are separated from impurities. For example, salt obtained from the sea is
separated from impurities; crystals of alum (Phitkari) are separated from
impure samples.
Question 10: Pragya tested the solubility of
three different substances at different temperatures and collected the data as
given below( results are given in the following table, as grams of substance
dissolved in 100 grams of water to form a saturated solution).
|
Substance dissolved |
Temperature in K |
||||
|
283 |
293 |
313 |
333 |
353 |
|
|
Potassium nitrate |
21 |
32 |
62 |
106 |
167 |
|
Sodium chloride |
36 |
36 |
36 |
37 |
37 |
|
Potassium chloride |
35 |
35 |
40 |
46 |
54 |
|
Ammonium chloride |
24 |
37 |
41 |
55 |
66 |
(a) What
mass of potassium nitrate would be needed to produce a saturated solution of
potassium nitrate in 50 grams of water at 313 K?
(b)
Pragya makes a saturated solution of potassium chloride in water at 353 K and
leaves the solution to cool at room temperature. What would she observe as the
solution cools? Explain.
(c) Find
the solubility of each salt at 293 K. What salt has the highest solubility at
this temperature?
(d) What
is the effect of change of temperature on the solubility of a salt?
Answer:10 (a) At 313 K, 62 grams of Potassium nitrate dissolved in 100 grams of water. So to produce a saturated solution of potassium nitrate in 50 grams of water, we need 62 x 50 = 31 grams of potassium nitrate 100
(b) Some
soluble potassium chloride will separate out in the form of crystals at room
temperature because the solubility of potassium chloride will decrease with
decrease in temperature.
(c)
(i) Solubility of Potassium nitrate at 293 K is 32 grams.
(ii) Solubility of Sodium chloride at 293 K is 36 grams. (iii) Solubility
of Potassium chloride at 293 K is 35 grams. (iv) Solubility of Ammonium
chloride at 293 K is 37 grams. The solubility of Ammonium chloride is highest
at this temperature.
(d) The solubility
of salt increases with increase in temperature
Soda water,
wood, air, soil, vinegar, filtered tea
Answer:11 Homogeneous mixtures: Soda water, air, vinegar
Heterogeneous mixtures: Wood, soil,
filtered tea
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