Class - VI Chemistry (Non IAS)
Chapter – 1
Chemistry and its Importance
1. Define chemistry.
A. The branch of science which deals with study of materials (substances), especially about their composition, methods of preparation, properties and their reactions with other substances is called chemistry.
2. How is chemistry useful in agriculture?
A. Chemistry has helped agriculture in the following ways:
i) It helped in the production of artificial fertilizers which increase food production.
ii) It helped in the production of better seeds.
iii) It helped in producing chemicals which kill insects (insecticides), fungi (fungicides) and unwanted herbs (herbicides).
3. How does chemistry helps us in the preservation of forests?
A. Due to fast dwindling forest reserves, the wood is being replaced by plastic and cotton is replaced by man made fibres such as rayon, nylon and terylene. Thus, chemistry helps us in conservation of forest wealth.
4. Name a few consumer products made by chemists. How are these products useful to us?
A. Plastic, rayon, nylon and terylene are a few consumer products made by chemists. These products help in conservation of forest wealth thus maintaining the balance of the eco-system.
5. How does chemistry help in the development of space research and electronics?
A. The present day space technology is the direct result of production of better and more powerful fuels which helped us to launch space satellites. Research in chemistry helped in making diodes which are used to make electrical circuits in radios, televisions, computers, calculators etc.
6. Why is boiling tube made from special glass?
A. A boiling tube is made from special glass as this glass expands very little on heating and does not crack.
7. Why is wire guaze placed under glass apparatus, when heated?
A. A wire guaze is placed under glass apparatus when heated as it distributes heat from the burner evenly to the glass apparatus and hence prevents its cracking.
CHAPTER-2
The Nature of matter
1. (i) Define solid.
A. Any material which has a definite shape and definite volume, such that it
can have any number of free surfaces, is called solid.
(ii) On the basis of molecular theory, explain why solids have a definite shape
and definite volume.
In solids, the molecules are very tightly packed and they cannot
interchange their position. So, solids have a definite shape and definite
volume.
2. (i) Define liquid.
A. Any material which has a definite volume, but no definite shape and has
one free surface, is called liquid.
(ii) On the basis of molecular theory, explain why liquids have a definite
volume but no definite shape.
In liquids, the molecules are not very tightly packed and are in a position
to interchange their places but cannot move far apart. So, liquids have a
definite volume and take the shape of the containing vessel as they do not
have a definite shape.
3. (i) Define gas.
A. Any material which has neither definite shape nor definite volume, is easily
compressible and has no free surface, is called gas.
(ii) On the basis of molecular theory, explain why gases have neither a
definite shape nor a definite volume.
In gases, the molecules are far apart from each other and the
intermolecular forces are almost negligible. So, the gases do not have a
definite shape or a definite volume.
4. Why can liquid flow , whereas solids can be heaped?
A. Solids have very small intermolecular spaces than liquids. So the solids have a
definite shape and volume whereas liquids have no definite shape but a
definite volume. So, liquids flow and solids can be heaped.
5. Why can liquids easily take the shape of the container but not solids?
A. In liquids, the intermolecular spaces between the molecules are far more as
compared to solids. Thus the molecules do not have a strong intermolecular force.
The molecules are in a position to interchange their places. It is on account of this
reason that liquids do not have a definite shape but take the shape of the containing vessel.
6. Why cannot we fill a cylinder with a gas?
A. In gases, the inter molecular spaces are too large and intermolecular forces are
almost negligible. So the gases can fill the entire space available to them and can
be easily compressed where as liquids can be very slightly compressed. So, we
cannot fill a cylinder with a gas.
7. i) State four important properties of metals.
A. Properties:
a) It has lustre ie., it has a shine or metallic glow.
b) It is a good conductor of heat and electricity.
c) It is ductile, i.e., it can be drawn into wires.
d) It is malleable i.e., it can be beaten into sheets.
ii) Write the symbols of the following metals.
a) Magnesium - Mg
b) Potassium – K
c) Iron - Fe
d) Silver – Ag
e) Lead – Pb
f) Sodium – Na
iii) Name the metals with the following symbols :
a) Na - Sodium
b) Al – Aluminium
c) Mn – Manganese
d) Ni - Nickel
e) Pt – Platinum
f) Au – Gold
8. i) State four important properties of non - metals.
A. Properties :
a) It has no lustre i.e., it cannot be polished.
b) It is a bad conductor of heat and electricity.
c) It is not ductile i.e., it cannot be drawn into wires.
d) It is not malleable i.e., it cannot be beaten into sheets.
ii) Write the symbols of the following atoms of non – metals:
a) Silicon – Si
b) Hydrogen- H
c) Chlorine – Cl
d) Nitrogen - N
iii) What do the following symbols stand for?
a) I – Iodine
b) O- Oxygen
c) S – Sulphur
d) Br- Bromine
e) P – Phosphorus
f) F - Fluorine
9. i) What do you understand by the following terms.
A. a) Atom : The smallest particle of an element, which may or may not have
independent existence but always takes part in a chemical reaction, is called an atom.
b) Molecule : The smallest unit of a pure substance which always exists independently and can retain all the chemical and physical properties of that substance is called molecule
ii) Write the symbols for the molecules of the following non-metals.
a) Hydrogen – H2
b) Oxygen – O2
c) Ozone – O3
d) Phosphorus – P4
e) Sulphur- S8
f) Iodine – I2
10. i) Define the term compound.
A. When the molecule of a pure substance consists of two or more atoms of different elements together in a definite ratio, then it is said to be a molecule of a compound.
ii) Define the term chemical formula:
A symbolic representation of the one molecule of a compound representing the number of atoms of various elements present in it, is called formula of a compound.
iii) What does a chemical formula represent?
a) It tells which elements are present in a compound.
b) It tells the number of atoms of each element present in a compound.
11. What does each of the following formulae represent?
A. i) 2H - It means two atoms of hydrogen.
ii) O2 - It means one molecule of oxygen has two atoms in it.
iii) 4H2O – It means that there are four molecules of water and the total number of various atoms in four molecules are eight atoms of hydrogen and four atoms of oxygen.
iv) CuSO4 – It means that a molecule of copper sulphate has one atom of copper, one atom of sulphur and four atoms of oxygen.
12. Write the number of atoms of each element the following molecules.
A i) Na2 CO3
Na – 2
C – 1
O – 3
ii) CuSO4
Cu – 1
S – 1
O – 4
iii) Al2(SO4)3
Al – 2
S – 3
O – 12
iv) H2SO4
H – 2
S – 1
O – 4
13. Write the chemical name of the following formulae:
A. i) HCl - Hydro Chloric acid
ii) NaOH – Sodium Hydroxide
iii) CaO - Calcium Oxide
iv) NaCl – Sodium Chloride
v) Na2 CO3 – Sodium Carbonate
vi) CuSO4 - Copper sulphate
14. Write the chemical formula of each of the following compounds.
A. i) Nitric acid – HNO3
ii) Calcium Oxide – CaO
iii) Sodium bicarbonate – NaHCO3
iv) Silver Nitrate - Ag NO3
v) Ferrous Sulphide - FeS
vi) Copper Sulphate – CuSO4. 5H2O
CHAPTER – 3
Pure Substances and Mixtures
1. (i) What do you understand by the terms
(a) Pure substance: A homogeneous material which contains particles of one
kind and has a definite set of properties is called a pure substance.
(b) Mixture : If two or more substances (elements or compounds or both) are
mixed together in any proportion, such that they don’t undergo any chemical
change but retain their individual properties then the resulting mass is called
mixture.
(ii) Name four substances which are pure substances, but are :
(a) Elements : nitrogen, oxygen, sulphur, gold.
(b) Compounds: Sodium chloride, calcium carbonate, magnesium oxide, carbondioxide.
2. Identify the pure substances and mixtures from the following list :
(i) Solid common salt – pure substance.
(ii) Milk – mixture
(iii) Air – mixture
(iv) Oxygen – Pure substance.
(v) Fruit juices – mixture
(vi) Brass – mixture
(vii) Copper sulphate crystals – pure substance
(viii) Distilled water – pure substance
(ix) Sugar solution – mixture
(x) Washing soda – pure substance
(xi) Honey – pure substance
(xii) Ammonium chloride – pure substance
(xiii) Lime stone – pure substance
3. By giving one example for each, define :
(i) Heterogeneous mixture: A mixture in which its constituents are not
distributed uniformly is called heterogeneous mixture.
Ex: Soil
(ii) Homogeneous mixture: A mixture in which its constituents are mixed
uniformly is called homogeneous mixture.
Ex: Salt solution
4. State four characteristics of a mixture.
(i) Variable composition : The constituents of a mixture are present in any ratio.
(ii) Physical change : The constituents of a mixture don’t bind each other by any
chemical force.
(iii) Homogenity : A mixture can be homogeneous or heterogeneous.
(iv) Separation of constituents : The constituents of a mixture can be separated
by employing suitable physical means.
5. Identify(i) homogeneous mixture and (ii) heterogeneous mixture from the following list.
(a)common salt solution – homogeneous
(b)A mixture of sand and salt – heterogeneous
(c) milk – homogeneous
(d) Brass – homogeneous
(e) Gun powder – heterogeneous
(f) Chocolate bar – heterogeneous
(g) Cooked vegetables of peas and cauliflower – heterogeneous
6. By giving two reasons prove that a powder containing iron and sulphur is a
Mixture but iron sulphide is a compound.
(i)A powder containing iron and sulphur is a mixture because the particles are not
evenly distributed whereas in iron sulphide the elements unite chemically in a
fixed proportion.
(ii) The powder of iron and sulphur is a mixture as the constituents can be
separated by physical means.
7. By giving two reasons prove that:
(i) Air is a mixture.
1) Air is a mixture of several gases,chief among them being nitrogen, oxygen,carbondioxide and water vapour which retain their individual properties.
2) Oxygen and nitrogen can be separated from the air by cooling them to very
low temperature.
(ii) Water is a compound.
1) The constituents of water cannot be separated by physical means such as
filtration, boiling etc;
2) The properties of water are entirely different from the properties of its
constituents.
8. Give four important differences between a mixture and a compound.
MIXTURE
(i) Nature: When two or more elements or compounds or both are mixed together in any proportion,such that they do not combine chemically, a mixture is formed.)(ii)Structure: Mixture may be homogeneous or heterogeneous.(iii) Composition: The constituents are present in any desired ratio.(iv) Separation of constituents: The constituents of a mixture can be separated by physical means.
COMPOUND
(i)Nature: When two or more elements unite chemically in a fixed proportion, a compound is formed.(ii)Structure: Compounds are always homogeneous.(iii) Composition: In case of compounds, the constituents are in a fixed ratio by weight. (iv) Separation of constituents: The constituents of a compound cannot be separated by physical means.
9. What do you understand by the following terms:
(i) Sedimentation: The method of separation of insoluble solids from its suspension by allowing it to stand still, such that the insoluble solid settles at the base of the surface.
(ii) Sediment: The insoluble solid which separates from its suspension.
(iii) Supernatant liquid: The clear liquid obtained after sedimentation.
(iv) Decantation: The process of pouring off as much clear liquid as possible without disturbing the sediment is called decantation.
(v) Centrifugation: The method of separating finely suspended particles in a liquid by whirling the liquid at a very high speed is called centrifugation.
(vi) Distillation: The process of separation of a liquid from a soluble salt solution by the evaporation of the liquid and recondensation of the vapours in another vessel is called distillation. .
(vii) Distillate: The pure liquid so collected from its salt solution by the combined process of distillation and condensation is called distilate.
10. What do you understand by the following terms:
(i) Filtration: The process of separation of insoluble solid constituents of a mixture from its liquid constituents by passing the suspension through a suitable porous material is called filtration.
(ii) Residue or precipitate: The insoluble solid constituents left on the filtering material when a suspension is filtered is called residue.
(iii) Filterate: The clear liquid obtained from the suspension of an insoluble solid and a liquid by the process of filteration is called filterate.
11. Describe an experiment for the preparation of pure ammonium chloride from a
A mixture of common salt and ammoniuim chloride.
Take a china dish and put in it a mixture of common salt and ammonium chloride with an inverted funnel.Heat the mixture over a low Bunsen flame. In a few moments,white fumes are seen to rise in the funnel.These fumes are of ammonium chloride.They gradually settle on the sides of funnel to form fine white powder.
Remove the funnel and scrap ammonium chloride from its walls.Repeat the process a few more times.Ammonium chloride completely separates.
12. Describe experiments to obtain the constituents of the following mixtures:
(i) A mixture of sand, saw dust and common salt.
Transfer the mixture in a beaker half-filled with wter. Stir the mixture well and allow it to stand for 10 minutes.The saw dust being lighter will float on the surface of water.The salt dissolves in water to form salt solution.The sand being heavy and insoluble settles at the base of beaker.Filter the solution taking care that sand is not disturbed.The saw dust will collect over the filter paper as residue.It can be dried in sunlight.The common salt solution collects as filtrate.
Transfer the common salt solution in a china dish.Heat the china dish on a sand bath.After sometime water evaporates leaving behind dry common salt.Add more water to the sand left in the beaker and stir. Filter the mixture.The sand is left as residue on the filter paper.Dry the sand in sunlight or hot air.
(ii) A mixture of iron filings,ammonium chloride and sand.
Roll a bar magnet in the mixture.The iron filings stick to the poles of the magnet.Scrap the iron filings from the magnet.Repeat the experiment a few more times till no more iron filings stick to the poles of magnet.If the mixture of ammoniuim chloride and sand are heated then white fumes of ammonium chloride are formed which gradually settle down on cooling to form fine white powder.Sand being heavy and insoluble settles at the base.
CHAPTER – 4
Changes Around Us
1. Classify the following changes as fast or slow changes:
Ans: (i) Germination of seed – slow change.
(ii) Milk changing to curd - slow change.
(iii) Burning of cooking gas in a gas stove- fast change.
2. Classify the following changes as reversible or irreversible changes:
Ans: (i)Stretching of a rubber band – reversible change.
(ii)Breaking of a glass tumbler – irreversible change.
(iii)Cooking of food – irreversible change.
3. Classify the following changes as desirable or undesirable changes:
Ans: (i)Formation of manure from dung – desirable change.
(ii)Melting of snow – desirable change.
(iii)Breaking of glassware – undesirable change.
(iv)Waste produced from plastic bags – undesirable change.
4. Classify the following changes as periodic or non-periodic changes:
Ans (i)A child on a swing – periodic change.
(ii)Rusting of an iron nail – non-periodic change.
(iii)Sneezing – non-periodic change.
(iv)Beating of heart - periodic change.
(v)Earthquake – non-periodic change.
5. (i)Define a physical change.
Ans: A change which alters some specific property of matter without any change in the
composition of its molecules is called physical change.
(ii)Give four examples of physical change.
a)Melting of ice
b)Freezing of water to ice.
c)Changing of water into steam by boiling.
d) Evaporation of water by the heat of sun.
6. i)Define a chemical change.
Ans. A change which alters the specific properties of a substance by bringing about a change in its molecular composition followed by a change in its state, is called chemical change.
ii) Give four examples of chemical change.
a) Cooking of food
b) Food turning bad after a few days.
c) Curdling of milk
d) Germination of seeds
7. Classify the following changes as physical change or chemical change:
Ans. i) Burning of food – chemical change
ii) Glowing of electric bulb – physical change
iii) A magnet attracting iron nails – physical change
iv) Burning of Magnesium ribbon in air – chemical change
v) Photosynthesis in plants - chemical change
vi) Moulding of glass – physical change
vii) Formation of fog – physical change
viii) Digestion of food – chemical change
8. Give four main differences between a physical and chemical change.
Ans.
Physical change
Chemical change
1. The change takes place only in state, colour, texture , electrical and magnetic properties. However, composition remains the same .
1. The change takes place in state, colour, texture etc., along with the change in composition.
2. No new substances are produced
2. New substances with new chemical properties are produced.
3. It is a temporary change and can be reversed .
3. It is a permanent change and can not be reversed.
4. There is no net absorption or release of energy.
4. There is always net absorption or release of energy.
CHAPTER – 5
AIR
percentage composition.
Ans: The four most important constituents of air are nitrogen(78%),oxygen(21%),
Carbondioxide(0.03%) and argon(0.9%).
2.(a)Name a major constituent of air which does not take part in combustion.
Ans: Nitrogen
(b)Name a constituent of air which is essential for combustion and respiration.
Oxygen
(c)Name a constituent of air which is essential for photosynthesis.
Carbondioxide
3.Briefly describe,how will you prove the presence of the following in air:
Ans: (i)Carbondioxide
Take a clean hard glass test tube.Pour about 4ml of lime water in it.Fix a cork
having two delivery tubes in the mouth of test tube.Suck the air from the tube which is not dipping in the lime water.Due to the suction,the pressure inside the test tube falls.Thus,air rushes in from the second tube and bubbles through the lime water.In a few minutes,lime water turns milky.This experiment proves that air contains carbondioxide.
(Refer fig.5.3. from page.51 of reader)
(ii)Water vapour
Take a clean glass tumbler.Wipe it from outside with a towel so that no water
is sticking to it.Take some crushed ice and put it in the glass tumbler.In a few
minutes,tiny droplets of water appear on the outer surface of glass tumbler.It
is because the water vapour present in air condense on the cooler surface of
glass tumbler.This proves that air contains water vapour.
(Refer fig.5.4. from page.52 of reader)
4. (i)What do you understand by the term fuel?
Ans: Any cheap material which burns in air or oxygen with the release of large amount of heat energy and light energy is called fuel.
(ii) Name any four common household fuels wood,coal,kerosene oil and LPG.
(iii) Name the products formed during the combustion of fuels carbondioxide,water vapour and heat.
5. How will you prove that air is necessary for the combustion of fuels?
Ans: Take a candle about 8cm long and fix it in a plastic trough.Pour water into the trough.Light the candle.Now invert a glass tumbler over the burning candle. The candle flame burns for a few seconds.The flame then starts flickering and finally goes off. The reason is that the burning candle does not receive any fresh supply of air on account of water seal.This proves that air is necessary for combustion.
(Refer fig.5.5 from page.53 of reader)
6. How will you prove experimentally that the products of combustion are:
(i)Carbondioxide gas and (ii)Water vapour.
Ans: Fix a funnel in an inverted position.To the stem of the funnel,connect a plastic tube which is connected on the other end to an absolutely dry U-tube containing small amount of anhydrous copper sulphate(white in colour). To the other end of U-tube,connect another plastic tube whose other end goes into a test tube containing fresh lime water.In the mouth of test tube,fix a suction tube. Light a candle under the funnel and start suction from the suction tube After a few minutes, the anhydrous copper sulphate (white) in the U – tube changes to blue colour. It is because, the anhydrous copper sulphate reacts with the water vapour to form blue coloured hydrated copper sulphate. The water vapour in the U – tube condenses to form liquid water. Thus, we can say that one of the products of combustion of candle is water vapour.
The lime water turns milky because it reacts with carbondioxide to form milky colour. So, carbondioxide is also one of the products of combustion of candle.
(Refer fig 5.6 from page. 53 of reader)
7. (i) What do you understand by the term respiration?
Ans: The collective process of absorption of oxygen (from air) into the blood stream and then oxidation of food materials in the cells with the release of heat energy, carbondioxide and water in the exhaled air is called respiration.
(ii) Briefly describe how the respiration takes place in human beings.
Our food mainly consists of compounds of carbon, hydrogen and oxygen, such as starch, sugar, fats, etc. These food materials break down in our digestive system to form simpler compounds. These simpler compounds mix in the blood stream and are carried to individual cells. At the same time oxygen (from inhaled air) dissolves in the blood stream in the lungs during the action of breathing. This dissolved oxygen in the blood is also carried to the individual cells. In the cells, the simpler compounds formed from the food materials react with oxygen to form carbondioxide and water with the release of heat energy. The heat energy is utilized for performing various body functions and in maintaining the body temperature at 370 C. The carbondioxide and water are exhaled.
8. How will you prove experimentally that plants produce carbondioxide gas during respiration?
Ans: Take a clean glass plate and over it place about 25g germinating seeds. Sprinkle some water over the seeds. Along with seeds place a small dish containing clear lime water. Place an inverted funnel over the germinating seeds and lime water. Plug the stem of funnel with cotton wool. Apply grease all along the rim of the funnel, So as to prevent the entry of air. Leave the apparatus undisturbed for overnight.
We find that lime water turns milky. It is because the germinating seeds give off carbondioxide during respiration. This shows that plants produce carbondioxide during respiration.
9. Give three differences between respiration and combustion.
Ans:
RESPIRATION COMBUSTION
1. Only heat energy is released 1. Heat as well as light energy is released.
2. It takes place at a fixed temperature of 370C 2. It takes place at comparatively very high temperature.
for human beings.
3. It is a slow process. 3. It is a fast process.
10. Explain briefly how the amount of oxygen in air does not deplete, in spite of the fact that large amount of
it is used in combustion and respiration.
Ans: Vast amount of oxygen present in air is consumed during the respiration of billions of plants and animals, which in turn release the vast amount of carbondioxide and water vapour. Furthermore, large amount of oxygen is consumed during the process of combustion of fuels.
During the daytime, the carbondioxide diffuses into the pores of green leaves here, it reacts with water, in the presence of chlorophyll to form Oxygen and glucose. The oxygen is released in the air. The glucose is converted into sugar and then starch by a very complex process. As the volume of oxygen released is equal to the volume of carbondioxide absorbed, therefore, amount of oxygen in the air does not get depleted.
CHAPTER – 6
WATER
1. State five important uses of water.
Ans: a) It is vital for sustaining animal and plant life.
b) It is essential to grow our food crops.
c) It is essential for cooking food.
d) It is essential for cleaning our bodies externally.
e) It is essential for a very large number of heavy industries.
2. Rain water is considered the purest form of natural water. Explain the statement. Name the gases which dissolve in rain water before it reaches the ground. What harm can be caused by these gases?
Ans: Rain water is the purest form of naturally occurring free water. It is because it is formed by natural distillation of surface water or sea water, by the heat of the sun.
Rain water contains some impurities. As rain drops travel through air, they pick up dust particles floating in the air. At the same time, they also dissolve a little oxygen and nitrogen and a fair amount of carbon dioxide gas. Carbon dioxide dissolves to form a weak acid called carbonic acid. When rocks containing lime are exposed to such water, the carbonic acid gradually dissolves them thereby causing erosion.
In the regions where heavy industry is located, the rain water dissolves a fair amount of sulphur dioxide, nitrogen dioxide, etc., which forms sulphuric acid and nitric acid. Thus, an acid rain is caused. It damages crops, forests, buildings, and environment in general.
3. List (i) three dissolved impurities, and (ii) three suspended impurities present in river water,
Ans: (i) a) Mineral salts which dissolve in river water from soil, especially salts of
calcium.
b) Dissolved gases like oxygen, carbon dioxide and hydrogen sulphide.
(ii) a) Clay and fine particles of sand.
b) Dead organic matter, such as wood, straw and dead animals.
c) Living matter of various kinds, such as bacteria, germs, etc.
4. Name the main salts present in the sea water and the percentage of one of them.
Ans: The main salts present in the sea water are common salt and salts of calcium and magnesium. The sea water contains 2.5% of common salt.
5. Describe an experiment to prove that plants give out a large amount of water vapour.
Ans: Take two beakers and in each of them pour 50 cc of water and 10 cc of oil. The oil will float above the surface of water and prevents evaporation of water.
Get a freshly cut twig from a plant and make it stand in one beaker. Place both the beakers in sunshine and cover them with dry bell jars having stoppers as shown in fig. 6.7. (page 64 of text book) Leave the apparatus undisturbed for two hours. The bell jar containing freshly cut twig has tiny droplets of water clinging to its sides. It is because the leaves of the twig give out water vapour in air.
6. Write a short note on water cycle.
Ans: The enormous amount of water vapour released into the air, rises up in the atmosphere as it is lighter than air. In the upper regions of atmosphere, the water vapour condenses to form tiny droplets of water called clouds. When the clouds contain too much of water they cause rain. The rain water flows over the surface of earth. Some amount of it gets collected within the earth as subsoil water. Ultimately, the water is either absorbed by plants or reaches to sea through rivers. Thus, a natural balance is built, i.e, the amount of water which vaporises is equal to the amount of water which returns to Earth in the form of rain.
7. State five qualities of drinking water.
Ans: a) It must be clear and colourless.
b) It must be odourless.
c) It must be free from harmful bacteria and suspended impurities.
d) It must contain dissolved gases like oxygen and carbon dioxide as they impart
freshness to water and give sparkling appearance.
e) It must contain small amounts of mineral salts of sodium, calcium and
magnesium as they give special taste to water.
8. State two ways by which a small amount of clear water can be made safe for drinking.
Ans: a) Small quantities of water can be made safe for drinking purpose by boiling it
for ten to fifteen minutes.
b) Water is treated with chlorine which kills germs and bacteria.
9. What do you understand by the following terms?
Ans: (i) Solute: A substance which dissolves in a liquid is called solute.
(ii) Solvent: A liquid which dissolves other substances in it, is called solvent.
(iii) Solution: A product formed by the dissolution of a solute into a solvent is
called solution.
(iv) Saturated solution: A solution which cannot dissolve more of a solute at a
given temperature is called saturated solution at that temperature.
(v) Solubility of a substance: The maximum amount of solute which will
dissolve in 100 g of water at a given temperature so as to form a saturated
solution is called solubility of the substance at that temperature.
10. How does pollution of water takes place?
(i) due to daily activities of men and animals?
Ans: In most of the rural India, people defecate in the open fields. Animals also defecate anywhere and everywhere. When it rains, the excreta of humans or animals is washed to streams and rivers. Thus, the potable water gets polluted.
(ii) Industries and agricultural operations?
Industries need large amount of fresh water. When this water is discharged, it contains metallic salts of mercury, lead, cadmium, chromium, arsenic, etc. These salts are highly poisonous in the nature. If the water polluted by the industries is directly discharged in rivers, it can kill the fish and water plants. If consumed by the animals or plants, it causes serious diseases.
During agricultural activities farmers use a variety of artificial fertilisers. They also spray the crops with very poisonous insecticides which are washed down to the rivers, thereby causing pollution of potable water. Sometimes these chemicals percolate through the soil and mix with the underground water. This causes pollution of the underground water.
11. How can the pollution caused by the activities of men and the industrial as well as agricultural operations be minimized?
Ans: In villages, the people should be encouraged to use pit latrines. In doing so, the excreta is converted into useful manure. Furthermore, it is not carried to rivers by rain water.
The waste water coming out of factories should be treated with chemical substances, so as to remove harmful metallic salts. The treated water should be discharged in rivers.
Agricultural pollution can be minimized by.
a) Use of minimum amount of artificial fertilizers.
b) Use of large amount of natural manure.
c) Use of minimum amount of artificial pesticides.
d) Use of natural pesticides such as neem oil.
e) Do not spray pesticides or manure in the fields when it is likely to rain heavily.
f) Use drip irrigation so that harmful chemicals do not percolate down.
CHAPTER – 7
Rocks and Minerals
1. (i) What is a rock?
Ans: A hard substance formed by the assembly of one or more inorganic minerals is
called rock.
(ii) What is an igneous rock?
The rocks formed from the cooling and solidification of extremely hot and
molten material, pushed up from the interior of the earth are called igneous rocks.
(iii) Briefly explain how the following rocks are : (a) granite (b) basalt.
a) Granite : If the rising magma, from the interior of earth loses its force and is
unable to penetrate crust of earth, then it solidifies with the crust of
earth to form a coarse grained rock, commonly called granite.
b) Basalt : The lava on solidification forms a fine grained hard rock commonly
called basalt.
2. Define sedimentary rock. Give four examples of sedimentary rock.
Ans: The rocks formed by the deposition of particles by the flowing water or wind are called sedimentary rocks.
Examples: Mudstone,Sandstone,Limestone,Dolomite.
3. Define metamorphic rock. Give two examples of metamorphic rock.
Ans: The rocks formed by the action of intense heat and pressure on sedimentary rocks,
such that their structure and texture change completely,are called metamorphic
rocks.
Examples:Slate,Marble.
4. (i) What do you understand by the term mineral?
Ans: Minerals are naturally occurring inorganic substances which may be made of
atoms of single element or more than one element, but having a definite chemical
composition.
(ii) State three characteristics of a mineral.
a) Minerals have a definite chemical composition.
b) Each mineral has a characteristic crystalline structure, which depends upon the arrangement of atoms in three dimensional pattern.
c) Minerals have a characteristic luster, colour, hardness and specific gravity.
5. (i) What is the difference between a diamond and a gem?
Ans: Crystals of ornamental value are called gemstones and diamond is an example of
gemstones.
(ii) State two uses of gems, in addition to their use as precious stones.
Gems reflect light and they are extremely hard.
6. (i) State any three uses of common salt.
Ans: a) Its purified form is used as table salt.
b)It is used for preserving fish, meat and also in pickles.
c) It is used in cleaning raw hides.
(ii) State any two uses of Plaster of Paris.
a) It is used for plastering fractured bones.
b) It is used for preparing moulds for statues.
(iii) Name the mineral from which lime is prepared. State any two uses of lime.
Ans. Lime is prepared by strongly heating limestone.
Uses:
a) Lime is extensively used as a mortar in construction industry.
b) It is also used in making glass by heating it with purified sand.
7. (i) What do you understand by the term soil?
Ans: Soil is the uppermost layer of land mass of the earth. It is a life supporting
medium, in which plants can grow.
(ii) Name one important ore of (a) aluminium (b) iron (c) copper.
(a) The main ore of aluminium is bauxite.
(b) The main ore of iron is haematite.
(c) The main ore of copper is cuprite.
8. Name the four important constituents of top soil.
Ans: The four important constituents of top soil are:
a) Rock or soil particles of different sizes.
b) Humus (organic matter)
c) Soil water.
d) Soil air.
9. Name the types of particles of soil in the decreasing order of size.
Ans: The types of particles of soil in the decreasing order of size are :
a) Gravel or stone – above 2.0 mm
b) Coarse sand – 0.20 to 2.0 mm
c) Fine sand – 0.02 to 0.20 mm
d) Silt – 0.002 to 0.02 mm
e) Clay – Below 0.002 mm
10. What is humus? Why is its presence important for the plants?
Ans: Humus is formed from the remains of the dead plants and animals by the activity of micro – organisms present in the soil. Humus is, thus, nothing but non – living organic matter. More the humus in the soil, more fertile it is.
11. Briefly explain the following:
Ans: (i) Sandy soils : Soils having 70 – 80 per cent of sand particles are called sandy soils. They are highly porous and have lots of air between the particles. They lack humus and cannot retain water. They are not suitable for the growth of plants. Most of the soil in deserts is sandy soil.
(ii) Clayey soils : Soils having more then 70 per cent clay particles and very little sand particles are called clayey soils. They have no or very little air between the soil particles. They have a poor drainage and can hold back water. Some amount of humus is present in this soil and hence plants can grow in it, provided there is sufficient drainage.
(iii) Loamy soils: Loamy soils are the best for the growth of plants. They contain humus and hold sufficient amount of air and water in the soil particles. This in turn permits proper root penetration and absorption of water and minerals from the soil.
12. Briefly explain the importance of water soluble nitrogen compounds in the fertility of soil.
Ans: Plants need nitrogen in the form of soluble compounds of nitrogen, for the manufacture of amino acids and proteins. It is the proteins which constitute the protoplasm of the plant cells and help in their growth and development. The soluble nitrogen compounds are present in the humus. Thus, the need for nitrogen is made up by the humus.
13. How does the soil get enriched with water soluble nitrogen compounds in :
Ans: (i) Nature: The nature compensates nitrogen in two ways.
a) By thunder and lightning: When the lightning occurs in the clouds, the nitrogen and oxygen in the air combine to form small amount of nitric oxide gas. The nitric oxide gas further reacts with oxygen to form nitrogen dioxide gas. The nitrogen dioxide gas then dissolves in water present in the clouds, to form traces of nitric acid. When it rains, the traces of nitric acid are washed down to the earth. On the earth, the nitric acid reacts with calcium carbonate or magnesium carbonate, present in the soil, to form calcium nitrate. The calcium nitrate is a soluble compound of nitrogen and hence makes up for the depleted nitrogen.
b) By symbiotic bacteria : Many pod bearing plants have nodules on their roots. These nodules contain symbiotic bacteria, which directly absorbs nitrogen from the air and converts it into soluble compounds of nitrogen.‘The symbiotic bacteria present in them continue their work and enrich the soil with soluble compounds of nitrogen.
(ii) With the help of farmer : A farmer applies natural manure in the fields to make up for the loss of nutrients and applies artificial fertilisers, such as urea, muriate of potash, potash, superphosphate of lime., etc., in adequate amount. This restores the fertility of the soil.
14. Briefly explain how the following fossil fuels are formed in nature :
Ans: (i) Coal:
Coal was formed in prehistoric times when huge forest areas got buried under the surface of the earth. Under humid and hot conditions, they were attacked by anaerobic bacteria which progressively removed hydrogen and oxygen, leaving behind carbon. Due to very high temperature and pressure of the Earth, the carbon got compact to form stony residue, called coal.
(ii) Petroleum:
Petroleum is formed by the anaerobic decomposition of extremely small sea animals and plants, which got buried under the surface of the earth millions of years ago.
15. Name a few problems created by the excessive use of fossil fuels.
Ans: The use of excessive amount of fossil fuels is gradually depleting the oxygen of atmosphere and increasing the amount of carbon dioxide. In addition to it, poisonous gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide are added into the atmosphere which are very harmful to the earth. The excessive carbon dioxide in the atmosphere is gradually raising the average temperature of the earth, which is extremely harmful for the environment.
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