Download Matter can be broadly divided into two major groups, `Pure` and

Is Matter around us Pure
Matter can be broadly divided into two major groups, 'Pure' and 'Impure'. In chemistry, the term 'purity'
acquires quite a different meaning from what we understand it to be in our day-to-day life.
Pure Substances
A pure substance has the same composition throughout. For example, different samples of water,
prepared by different methods, by different people at different places always consist of hydrogen and
oxygen in the ratio 1:8 by mass and 2:1 by volume.
Impure Substances - Mixtures
Impure substances are commonly called mixtures. A mixture is a material containing two or more
elements or compounds that are in close contact and are mixed in any proportion.
Separation of the Constituents of Mixtures
The separation of the various constituents of different mixtures depends on the properties of the
constituents.
Types of Solutions
Solution is defined as a homogeneous mixture of two or more chemical substances. The state of
matter of a solution may be solid, liquid or gas. For example: common salt in water (liquid solution), air
(gaseous solution), alloys (solid solution), etc.
Physical and Chemical Changes
Matter undergoes certain changes as a result of the application of energy. Water from saltpans on the
seacoast dry up, leaving behind salt; water from the sea evaporates to from water vapour, which convert
into clouds and then condense to form rain.
Summary
Matter is anything that occupies space and has mass
Element is a pure substance, which can neither be decomposed nor built from simpler substances by any
physical or chemical means. It contains only one kind of atom.
Broadly speaking, elements can be divided into metals, non-metals, metalloids and noble gases
A compound can be decomposed into two or more simpler substances. In its formation, energy is usually evolved
or absorbed.
The smallest particle of an element or a compound, which can exist in the free state, is called a molecule.
Impure substances are mixtures. They can be a mixture of elements or compounds or both, mixed in any
proportion. Each constituent of the mixture exhibits its own properties.
Constituents of a mixture can be easily separated while components of a compound cannot be separated easily.
Sedimentation followed by Decantation is used to separate an insoluble solid from a liquid.
Filtration is a more effective method of separating an insoluble solid from a liquid.
A soluble solid can be obtained back from a liquid in which it dissolves by the process of evaporation.
Distillation is employed to separate and re-obtain both the solute and the solvent from a solution.
Fractional Distillation is used to separate two miscible liquids whose boiling points differ by at least 30 0C.
Chromatography is based on the difference in absorption of different substances on the surface of a solid medium
that is used to separate a mixture, containing components in minute quantities.
True solution is a homogenous mixture of a solute and a solvent with high degree of dispersion where the
particles are between 0.1 nm to 1 nm.
Solutions can be aqueous or non-aqueous, saturated or usaturated, concentrated or dilute.
Solubility is defined as the number of grams of a solute that dissolves in 100g of a solvent to form a saturated
solution at a given temperature and pressure.
Suspension is a heterogeneous system consisting of particles of a solid bigger than 100 nm to 200 nm
suspended in a liquid medium
Colloidal state is a heterogeneous dispersion of two immiscible phases where the size of a colloidal particle lies
between 1-100 nm.
A chemical change is a permanent, irreversible change in which a substance changes in its composition
producing one or more new substances.
A physical change is a temporary and reversible change in which the physical properties of the substance change
without altering the composition of the substance.
Question (1): Define an element.
Answer: A pure substance that cannot be broken into two or more simpler substances by physical and
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chemical means is called an element.
Name
Question (2): Mention whether the following statements are true or false. Correct the false statements. a) An
aqueous solution of copper sulphate is homogeneous. b) Milk is a pure substance. c) A molecule of sulphur is
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monoatomic.
Subject
Answer:
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a) True
b) False. Milk is a mixture and thus an impure substance
c) False. A molecule of sulphur is polyatomic i.e., it has 8 atoms per molecule.
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Question (3): Classify the following as element, compound or mixture. i) Zinc amalgam (ii) Sea water (iii)
Iodine vapour (iv) Gold coin (v) Water.
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Answer: i) Mixture
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iv) Mixture
v) Compound.
Question (4): Give the characteristics of a pure substance.
Answer: A pure substance is,
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 Impure Subs
a) Homogeneous in nature
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of Mixtures
b) Has a definite set of properties
 Types of So
c) Has a composition, which cannot be altered by physical means.
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Question (5): Give two differences between elements and compounds.
Physical and
Changes
 Summary
 Question an
 Multiple Cho
Answer:
Question (6): How would you separate a mixture of ammonia and hydrogen?
Answer: Passing the mixture through water can separate the mixture of ammonia and hydrogen. Ammonia
being highly soluble dissolves in water while H2 passes out as gas.
Question (7): Give one example for each of the following mixtures: i) Solid/solid (homogeneous) ii) Solid/solid
(heterogeneous) iii) Liquid/liquid (homogeneous) iv) Liquid/liquid (heterogeneous) v) Gas/liquid
(homogeneous).
Answer: i) Brass
ii) Clay
iii) Ethyl alcohol + water
iv) Oil and water
v) Soda water.
Question (8): Action of heat on blue vitriol is a physical as well as chemical change. Justify.
Answer: When blue vitriol is a gradually heated to about 800 oC, it undergoes a physical change to form a
white powder. On adding a drop of water to the white powder, it changes back to blue. Thus the change is a
physical change. On strongly heating, copper sulphate (blue vitriol) decomposes to give new substances like
copper oxide and sulphur dioxide. On cooling these, copper sulphate cannot be re-obtained. Thus it is a
chemical change.
Question (9): How would you separate a mixture of NH4Cl and I2?
Answer: Heating cannot separate the mixture, as both substances sublime on heating. However, when water
is added to the mixture, NH4Cl dissolves but I2 does not. The mixture is filtered. The filtrate is a solution of
NH4Cl, while the residue is iodine. The filtrate is heated to obtain NH 4Cl crystals.
Question (10): How can you prove that air is a mixture?
Answer: a) The composition of air is variable. The composition varies from place to place and with altitude.
For instance, at higher altitudes, there is less oxygen in the air. In industrial areas, due to the waste gases
coming out of industrial chimneys in the form of smoke more impurities are added in the air.
b) Air has no definite set of properties. Its properties are an average of its constituents. For e.g., vapour density
of oxygen is 16, vapour density of nitrogen is 14 and vapour density of air is 14.4
c) The components of air can be separated by physical means. Fractional distillation of liquid air can separat2
and O2. Boiling point of a liquid N2 = -1960 C, Boiling point of a liquid O2 = -1830 C
d) The formation of air does not involve any energy change. No energy is released or absorbed when the
constituents of air are mixed in the right proportion. e) Air cannot be assigned a fixed chemical formula.
Question (11): Describe a method for separation of the constituents of gunpowder.
Answer: Gunpowder is a mixture of sulphur, charcoal and potassium nitrate (nitre). When water is added to
the mixture potassium nitrate dissolves. The mixture is then filtered. The filtrate is potassium nitrate solution
while the residue is a mixture of sulphur and charcoal. The filtrate is evaporated on a sand bath to obtain nitre
back. When carbon disulphide is added to the residue, sulphur dissolves. When this mixture is filtered the
filtrate is sulphur solution while the residue is charcoal. Leaving it open evaporates the sulphur solution. Carbon
disulphide evaporates and sulphur crystals are left behind.
Question (12): Write down the technique used to separate. i) The constituents of the colouring matter in ink. ii)
Hydrated copper (II) sulphate from its aqueous solution. iii) Unused zinc, after reacting the excess with dilute
sulphuric acid. iv) Benzene (boiling point 800 C) and aniline (boiling point 1840 C).
Answer: i) Chromatography
ii) Evaporation
iii) Filtration
iv) Fractional distillation
Question (13): A pupil decides to separate powdered calcium carbonate from powdered sodium chloride by
shaking the mixture with water and filtering. Would this procedure succeed? Explain.
Answer: This procedure will succeed, as CaCO3 is insoluble in water while NaCl is soluble in water. On
filtering the residue will be CaCO3.
Question (14): Give four characteristics of a physical change
Answer: a) A physical change is temporary and is usually reversible.
b) No new substances are formed during a physical change.
c) There is no change in mass of the substance during a physical change.
d) There is no net absorption or release of energy during a physical change.
Question (15): How would you remove? i) Grease spots from clothes. ii) Obtain pure water from seawater. iii)
Obtain hydrogen from a mixture of H2 and Cl2. iv) Iodine stains.
Answer: i) Grease spots from clothes can be removed by using turpentine oil in which grease dissolves.
ii) Distillation.
iii) Pass the mixture of H2 and Cl2 into a porous pot. H2 diffuses in faster than Cl2 into the porous pot. Most of
the Cl2 remains outside the porous pot.
iv) Iodine dissolves in ethyl alcohol.
Question (16): In the formation of sodium chloride from its constituent elements, do the properties of its
elements change. Explain.
Answer: Sodium is a very reactive metal that reacts exothermically with water. If we were to ingest a pinch of
sodium, it would burn our intestines. Chlorine is a greenish yellow gas with a characteristic irritating odour and
pungent taste. When sodium and chlorine combine to form sodium chloride, the properties of the elements are
totally changed. Sodium chloride is a white substance totally safe to be ingested and is used to add flavour to
our food.
Question (17): Give an example of each of the following types of mixtures. (a) Solid and liquid (b) Solid and
gas (c) Liquid and solid (d) Liquid in gas
Answer: a) Tea leaves in water.
b) Dust particles in air.
c) Amalgam of mercury and copper.
d) Clouds carrying moisture.
Question (18): Describe how you would obtain the substances mentioned below, from the given mixtures. a)
Iodine from tincture of iodine. b) Lead chloride from a mixture of lead chloride and silver chloride.
Answer: a) Iodine dissolved in alcohol is called tincture of iodine. Alcohol is a volatile liquid. So the mixture
can be kept open or warmed in a water bath. Alcohol will evaporate leaving behind the iodine crystals.
b) Add hot water to the mixture of lead chloride and silver chloride. Lead chloride (PbCl 2) is soluble in hot water
and it dissolves. Silver chloride (AgCl) is insoluble in hot water and so the mixture should be filtered
immediately. The filtrate is the solution of PbCl2 and the residue is AgCl. The filtrate is heated to obtain crystals
of PbCl2.
Question (19): Differentiate between a homogeneous mixture and a heterogeneous mixture.
Answer:
Question (20): Briefly describe how to separate, i) Sulphur from a mixture of sulphur and sand. ii) Black CuO
from a mixture of CuO and ZnO.
Answer: i) Add a solvent to the mixture of sulphur and sand. Sulphur dissolves in carbon disulphide while
sand does not. When filtered, the residue is sand. The filtrate is kept open, carbon disulphide evaporates and
the sulphur crystals form.
ii) Add a solvent to the mixture of CuO and ZnO that dissolves only one component e.g. sodium hydroxide.
When sodium hydroxide is added to the mixture, ZnO dissolves. Filter to obtain the residue of CuO.
Question (21): Classify the following properties as those belonging to compounds and mixtures. a) A chemical
change. b) Always homogeneous. c) Particles are of different kinds. d) No energy change involved in its
formation.
Answer: a) Compound b) Compound c) Mixture d) Mixture.
Question (22): What is the difference between? i) A mixture of iron filings and sulphur and ii) sulphur heated
with iron?
Answer: When iron filings and sulphur are mixed, the mixture formed has both the components. They retain
their individual distinct properties. They need not be present in any fixed proportion by mass. In contrast, when
iron filings and sulphur are heated together they form a new compound, iron sulphide that has distinct
properties when compared to the combining elements. Iron and sulphur in a mixture can be separated using a
magnet. The compound iron sulphide cannot be separated into its elements.
Question (23): What is the concentration of a solution in terms of mass percentage if it contains 20 g of a salt
in 250 g of water?
Answer: Mass of the solute (salt) = 20 g
Mass of the solvent (water) = 250 g
Mass of the solution = Mass of the solute + Mass of the solvent
= 20 + 250 = 270 g
Mass percentage of solution =
= 7.4%
Question (24): How are true solution, colloidal solution and suspensions different from each other?
Answer: The difference between solution, colloids and suspension are summarized in the following table.
Question (25): If salt is added to water, is the mixture homogeneous or heterogeneous. Give reasons for your
Answer.
Answer: The mixture is homogeneous because
a) The salt particles do not form a separate layer.
b) The salt particles cannot be separated from the water by filtration.
c) Also every portion of the solution is equally salty, as the solution has salt uniformly dispersed in it.
Question (26): Classify as physical or chemical change. a) Tearing of paper. b) Production of biogas c) Butter
going rancid.d) Magnetisation of iron e) Clotting of blood.
Answer: a) Physical - No change in mass.
b) Chemical - New substances with new properties are produced.
c) Chemical - New substances are formed and the original substances cannot be re-obtained.
d) Physical - Temporary, no new substance is formed.
e) Chemical - New substance with new properties is produced. Unclotted blood cannot be re-obtained in this
change.
Is Matter Around us Pure
Question (1): A mixture of oil and water is an example of _____________.
1. compound
2. two elements
3. mixture
4. true solution
Ans: 3
Question (2): A mixture of mercury and copper is an example of _______.
1. solid and solid
2. liquid and solid
3. solid and liquid
4. liquid and liquid
Ans: 2
Question (3): Which of these elements is not a metalloid?
1. Tungsten
2. Germanium
3. Bismuth
4. Antimony
Ans: 1
Question (4): Which one of the following is monoatomic?
1. Oxygen
2. Hydrogen chloride gas
3. Argon
4. Ammonia
Ans: 3
Question (5): Which of the following is not a mixture?
1. Blood
2. Silver coins
3. Saliva
4. Plutonium
Ans: 4
Question (6): Which property does not describe a compound?
1. It is a pure substance.
2. It is mixed in any proportion by mass.
3. It cannot be separated into constituents by physical means.
4. It is composed of two or more elements.
Ans: 2
Question (7): The quantity of solute present in a given amount of solution represents_______
1. solubility
2. concentration
3. sublimity
4. saturation
Ans: 2
Question (8): In a colloidal solution________
1. the size of a colloidal particle lies roughly between 0.1 nm to 1 nm.
2. the particles have a tendency to settle when the solution is left standing.
3. the particles pass through ultrafilter papers and animal and vegetable membranes.
4. the dispersed phase is uniformly distributed in the dispersion medium
Ans: 4
Question (9): When sodium oxide reacts with water it undergoes chemical change to form ________.
1. hydrogen
2. sodium hydroxide
3. sodium nitride
4. sodium chloride
Ans: 2
Question (10): Chemical changes are __________.
1. temporary, reversible and a new substance is produced
2. always accompanied by exchange of light
3. permanent, irreversible and a new substance is produced
4. never accompanied by exchange of light and heat energy
Ans: 3
Question (11): Which pair is a miscible liquid mixture?
1. Methyl alcohol and acetone
2. Mercury and alcohol
3. Benzene and water
4. Carbon disulphide and water
Ans: 1
Question (12): Iron rod turns red on heating. The change is a______
1. physical change
2. temporary
3. physical and chemical change
4. chemical Change
Ans: 1
Question (13): Which one of the following does not sublime?
1. Camphor
2. Charcoal
3. Naphthalene
4. Iodine
Ans: 2
Question (14): Which technique is used to separate a solid-solid mixture?
1. Sedimentation
2. Evaporation
3. Distillation
4. Sublimation
Ans: 4
Question (15): On adding excess salt to a solution, it shows no change in solubility. This shows________
1. crystallization
2. slow Diffusion
3. saturation
4. dissolution
Ans: 3
Question (16): The process used to separate a mixture of ammonium chloride and iodine is ______.
1. sublimation
2. magnetic separation
3. solvent extraction
4. chromatography
Ans: 3
Question (17): An example of a chemical change is _____.
1. formation of clouds
2. glowing of an electric light
3. dropping sodium into water
4. dissolving of salt in water
Ans: 3
Question (18): A true solution is a _________.
1. homogeneous mixture
2. heterogeneous mixture
3. pure compound
4. impure compound
Ans: 1
Question (19): Fractional crystallization is used to separate which of the following?
1. Two solids
2. Two liquids
3. Two gases
4. A solid and a liquid
Ans: 1
Question (20): Tyndall Effect in colloids is due to _________.
1. dispersion of light
2. merging of light rays
3. scattering of light
4. convergence of light rays
Ans: