''AKC SCIENCE CLASSES"
CLASS 09 TH (CBSE AND MP BOARD)
"CHAPTER 02"
"IS MATTERS AROUND US PURE"
"EXERCISE QUESTIONS"
Question 01:- 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.
Solution:-
(a) Evaporation
(b) Sublimation
(c) Filtration
(d) Chromatography.
(e) centrifugal machine or churning the curd by hand.
(f) Decantation
(g) Filtration.
(h) Magnetic Separation.
(i) Winnowing.
(j) Coagulation and decantation.
Question 02:- Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Ans:- Method of preparation of tea
(i) Take some water (solvent) in a pan and heat it.
(ii) Add some sugar (solute) and boil to dissolve the sugar completely the obtained homogeneous mixture is called solution.
(iii) Add tea leaves (or tea) in the solution and boil the mixture.
(iv) Now add milk and boil again.
(v) Filter the mixture through the tea stainer and collect the filtrate or
soluble substances, i.e., tea in a cup. The insoluble tea leaves left behind
as residue in the 8 trainer.
Question 03:- 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. Which salt has the highest
solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a
salt?
Ans:-
(a). Mass of potassium nitrate needed to produce its saturated solution
in 100 g of water at 313 K = 62 g
Mass of potassium nitrate needed to produce its saturated solution in
50 g of water at 313
62
K = ------- x 50g = 31g
100
(b). Crystals of potassium chloride are formed. This happens as solubility
of solid decreases with decreasing the temperature.
(c). Solubility of each salt at 293 K
Potassium nitrate 32 g per 100 g water
Sodium chloride 36 g per 100 g water
Potassium chloride 35 g per 100 g water
Ammonium chloride 37 g per 100 g water
[Note:- Solubility of a solid is that amount in gram which can be dissolved
in 100 g of water (solvent) to make saturated solution at a particular
temperature.]
Ammonium chloride has the maximum solubility (37 g per 100 g of
water) at 293 K.
(d). Solubility of a (solid) salt decreases with decrease in temperature
while it increases with rise in temperature.
Question 04:- Explain the following giving examples.
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Ans:-
(a) Saturated solution :- A solution in which no more amount of solute can
be dissolved at a particular temperature is called saturated solution.
Example: when sugar is dissolved repeatedly in a given amount of
water, a condition is reached at which further dissolution of sugar is not
possible in that amount of water at room temperature.
(b) Pure substance :- A substance made up of single type of particles
(atoms and/or molecules) is called pure substance. All elements and
compounds are said to be pure,
Example :- water, sugar etc.
(c) Colloid :- A heterogeneous mixture in which the solute particle size is
too small to be seen with the naked eye, but is big enough to scatter
light is known as Colloid. There are two phases in colloidal solution
Dispersed phase: solute particles are said to be dispersed phase
Dispersion medium: the medium in which solute particles are spread is
called the dispersion medium.
Example :- Milk, clouds etc., are the example of colloid.
(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. Particles of suspension are visible to the naked eye.
Example :- Mixture of sand, Water and Muddy water etc.
Question 05:- Classify each of the following as a homogeneous or
heterogeneous mixture. Soda water, wood, air, soil, vinegar, filtered tea.
Ans:- Homogeneous mixtures:- Air, soda water, vinegar, filtered tea.
Heterogeneous mixtures:- Wood, soil.
Question 06:- How would you confirm that a colorless liquid given to you is pure water?
Ans:- If the given colorless liquid boils at 100°C sharp, it is pure water, otherwise not.
Question 07:- 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
Ans:- Ice, iron, calcium oxide, mercury are pure substance as they
have definite composition.
Milk is a colloid, so it is a heterogeneous mixture.
Hydrochloric acid is also a mixture of hydrogen chloride gas and water.
Question 08:- Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Ans:- Sea water, air and soda water are Homogeneous mixture.
Coal, Soil are Heterogeneous solution.
Question 09:- Which of the following will show "Tyndall effect"?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
Ans:- Milk and starch solution will show "Tyndall effect" as both of
these are colloids.
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
Ans:-
Elements :- Sodium, silver, tin and silicon.
Compounds :- Calcium carbonate, methane, and carbon dioxide.
Mixtures :- Soil, sugar solution, coal, air, soap and 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
Ans:- Growth of a plant, rusting of iron, cooking of food, digestion of
food, burning of a candle are chemical changes, because here the
chemical composition of substance changes.
