TEXTBOOK ANSWERS AND SOLUTIONS OF CBSE CLASS IX SCIENCE CHAPTER 2 Is Matter Around Us Pure

1) Which separation techniques will you 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:-a) Evaporation
b) Sublimation
c) Centrifugation or
filtration or decantation
d)Chromatography
e)Centrifugation
f) Using separating funnel
g)Filtration
h)Magnetic separation
i)Winnowing
j)Centrifugation
2) Write the steps you would use for making tea. Use the words:
solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
ANSWER:-First, water is taken as a solvent in a saucer pan. This
water (solvent) is allowed to boil.
During heating, milk and tea leaves are added to the solvent as
solutes. They form a solution.
Then, the solution is poured through a strainer. The insoluble
part of the solution remains on the strainer as residue. Sugar is added to the
filtrate, which dissolves in the filtrate. The resulting solution is the
required tea.
3. 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).
(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 :-(a) Since 62 g of potassium nitrate is dissolved in 100g
of water to prepare a saturated solution at 313 K, 31 g of potassium nitrate
should be
dissolved in 50 g of water
to
prepare a saturated solution at 313 K.
(b) The amount of potassium chloride that should be dissolved
in water to make saturated solution increases
with temperature. Thus, as the solution cools some of the potassium chloride will precipitate out of the solution.
(c) The solubility of the salts at 293 K are:
Potassium nitrate 32 g
Sodium chloride 36 g
Potassium chloride 35 g
Ammonium chloride 37 g
Ammonium chloride has the highest solubility at 293 K.
(d) The solubility of a salt increases with temperature.
4) Explain the following
giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
ANSWER :-(a) Solution in which no more solute can be dissolved at
a
particular temperature is known as saturated solution. For example
in aqueous solution of sugar no more sugar can be dissolved at room
temperature.
(b) A pure substance is a substance consisting of a single type of
particles i.e., all constituent particles of the substance have the same
chemical properties. For example
water, sugar, salt etc.
(c) A colloid is a heterogeneous mixture whose L particles are not as small as solution but they are so small
that cannot be seen by naked
eye. When a beam of light
is
passed through a colloid then the path of the light becomes visible. For example milk, smoke etc.
(d) A suspension is a heterogeneous mixture in which solids are dispersed in liquids. The solute particles in suspension do not dissolve but remain suspended throughout the medium. For example Paints, Muddy water chalk water mixtures
etc.
5) Classify each of the following as a homogeneous or
heterogeneous mixture. Soda water, wood, air, soil, vinegar, filtered tea
ANSWER: –   Homogeneous mixtures: Soda water, air,
vinegar
Heterogeneous mixtures: Wood, soil, filtered tea
6) How would you confirm
that a colourless liquid given to you is pure water?
ANSWER:-Take a sample of colourless liquid and put on stove if it
starts boiling exactly at 100
ºC then it is pure water. Any other colourless liquid such as vinegar
always have different
boiling point. Also observe carefully that after some time whole liquid will convert into vapour without leaving any residue.
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:-
(a) Ice
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
8) Identify the solutions
among the following
mixtures:
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
ANSWER:-
(b) Sea water
(c) Air
(e) Soda water
9) Which of the following
will show the
Tyndall effect?
(a) Salt solution
(b) Milk
(c) Copper sulphate
solution
(d) Starch solution
ANSWER:-Milk and starch
solution will show the
Tyndall effect.
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:-Elements
(a) Sodium
(d) Silver
(f) Tin
(g) Silicon
(e) Calcium carbonate
(k) Methane
(l) Carbon dioxide
Mixtures
(b) Soil
(c) Sugar solution
(h) Coal
(i) Air
(j) Soap
(m) Blood
11) Which of the
following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron
fillings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of candle
ANSWER:-
(a) Growth of a plant
(b) Rusting of iron
(d) Cooking of food
(e) Digestion of food
(g) Burning of candle