VII CLASS - CHEMISTRY (NON IAS)

Class - VII Chemistry (Non IAS)

Chapter- 1. Elements and Compounds

1. Define an element.
A. Any pure substance which cannot be broken into two or more simpler substances by any chemical means is called an element.
2. How many elements have been discovered by the chemists? What are normal and harmful elements?
A. Chemists have discovered 114 elements. Among these 82 elements are normal and 32 elements are radio active and harmful elements.
Normal elements: The elements which do not give out any harmful radiations are called normal elements.
Harmful elements: The elements which give out harmful radiations are called harmful or radioactive elements.

3. Define the term metal and name 6 common metals along with their symbols.
A. Metal : An element is a metal if it has lustre, is a good conductor of heat and electricity, is malleable and ductile and has high melting point and boiling point.
1) Sodium – Na, 2) Calcium – Ca
3) Magnesium- Mg 4) Gold- Au 5) Iron- Fe 6) Nickel – Ni.

4. Define the term non- metal and write the names and the symbols of 3 non- metals (solid gases) and 1 non- metal which is a liquid.
A. Non- metal : An element is a non- metal at room temperature, has no lustere, is bad conductor of heat and electricity, is non – malleable and non- ductile and has low melting point and boiling point.


3. Non – metals (Solids)
i) Iodine - I
ii) Sulphur – S
iii) Phosphorous – H

3 Non – metals – (gases)

i) Hydrogen- H
ii) Nitrogen – N
iii) Oxygen – O

1. Non- Metals (liquid)
i) Bromine- Br


5. What are noble gases? Give the names and symbols of four noble gases.

A. Noble gases: The elements found in air in small traces in gaseous state which do not react chemically with any other element are called noble gas or Inert gases or rare gases.

Names and symbols of 4 noble gases are:

1. Helium – He
2. Neon- Ne
3. Argon – Ar

6. Define a) an atom b) a molecule. Give three examples of each molecule which has similar and different kinds of atoms.
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.

Molecule : The smallest unit of a pure substance which always exist independent and can retain all the chemical and physical properties of that substance is called an molecule.

Molecules of same Molecule of different
kind of atoms kinds atoms

N N Na cl
Molecule of Nitrogen Molecule of sodium Chloride

O O O S O
Molecule of oxygen Molecules of SO2

Cl Cl 4
Molecule of chlorine Molecule of methane

4 --- C -- 4

4


7. What do you understand by the term compound?
A. When the molecule of a pure substance contains two or more atoms of different elements compound together in a definite ratio then it is said to be a molecule of a compound.


8. What does each of the following formulae represent?
i) 20 ii) H2 iii) 10H2O iv) 4 Cl v) 5CO2 vi) FeS

A.
i) 20 : It means two atoms of oxygen .
ii) H2 : It means two atoms of Hydrogen.
iii) 10H2O : If means there are ten molecules of water, and further 20 atoms of Hydrogen and 10 atoms of oxygen.
iv) 4 Cl :- It means 4 atoms of chlorine.
v) 5CO2 : It means there are 5 molecules of carbon dioxide and further 5 atoms of carbon and 10 atoms of Oxygen.
vi) FeS : If means one atom of Iron and one atom of sulphur.

9. Write the number of atoms of each element in the following:-
i) K2CO3 ii) Fe SO4 iii) Pb (NO3)2 iv)Na2S
v) Fe2(SO4)3 vi) Pb3O4

A. i) K2CO3 - 2 atoms of potassium and 1 atom of carbon and 3 atoms of oxygen.

ii) FeSO4 – 1 atom of Iron, 1 atom of sulphur 4 atoms of oxygen.
iii) Pb (NO3)2 : 1 atom of lead, 2 atom of Nitrogen and 6 atoms of
Oxygen.
iv) Na2S - 2 atoms of Sodium and 1 atom of sulphur.

iv) Fe2(SO4)3 : 2 atoms of Iron, 3 atoms of sulphur and 12 atoms of Oxygen.
v) Pb3O4:- 3 atoms of lead and 4 atoms of oxygen.

10. Write the chemical names of the following compounds:
i) H2SO4 – ii) NaOH iii) Na2CO3 iv) CuSO4
v) NaHCO3 vi) CH4

i) H2SO4 - Sulphuric acid
ii) NaOH - Sodium hydroxide
iii) Na2Co3 - Sodium Carbonate
iv) CuSO4 - Copper Sulphate
v) NaHCO3 - Sodium bicarbonate
vi) CH4 - Methane

11. Write the chemical formulae of each of the following chemical compounds.
A. i) Hydro chloric acid - HCl
ii) Calcium oxide - CaO
iii) Ferrous sulphide - FeS
iv) Sodium sulphide - Na2S
v) Zinc Sulphate - ZnSO4
vi) Copper oxide - CuO
12. i) Name two particles found inside the nucleus of any atom and
state their mass and charge.
ii) Name the kind of particles which revolve around the nucleus and state their mass and charge.

A. i) The particles found within the nucleus of an atom are called nucleons.
The positively charged particles having a unit positive charge and mass equal to 1 amu, located within the nucleus of an atom are called protons.

ii) The particles revolving around the nucleus of an atom, with mass 1837 times the mass of 1 hydrogen atom and has a unit negative charge, are called electrons.
Electrically neutral particles found without the nucleus of an atom having a mass of 1 amu are called neutrons.

13. i) What do you understand by the term valency?
ii) What kind of valency do the metals generally have?
iii) Name three elements each whose ions have valency 1 + 2 + 3 respectively.

A. i) The number of electrons donated or accepted by an atom of an element so as to have 8 electrons in its outer most shell is called valency.
ii) Generally they have electropositive valency.

Mono valent ion ® Hydrogen
Formula ® H+
Divalent ion ® Magnesium
Formula ® Mg2+
Trivalent ion ® Ferrium
Formula ® Ferric ion (Fe3+)

14. i) What kind of valency do the non – metals generally have?
ii) Name a non – metal / group of non- metals.

A. i) Generally the non – metals have electro negative valency.
ii) Chloride Cl- . Bromide Br-, Iodide I- , Hydride H- , NO3 – Nitrate etc.

15. i) What is variable valency?
ii) Give 3 examples of elements having variable valency.

A. i) An element which exhibits more than one valency, is said to have variable valency.
ii) Metal Lower Valency Higher valency
Iron (Ferrum) Ferrous (Fe2+) Ferric (Fe3+)
Copper (Cuprum) Cuprous (Cu+) CupriC (Cu2+)
Mercury Mercurous (Hg+) Mercuric Hg2+

16. State 4 differences between physical and chemical changes.
A.

Physical change
Chemicals Change
1. The change takes place only in state, colour, texture, electrical and magnetic properties. How over, composition remains the same.
1. The change takes place in state, colour textures, etc., along with the change in composition.
2. Specific properties of the substance do not change
Specific properties of a substance change completely.
3. It is a temporary change and can be reversed.
3. It is a permanent change and cannot be reversed.
4. There is no net absorption or release of energy
4. There is always net absorption or release of energy.


17. Write the formulae of the following salts by criss- cross method.
A. i) Sodium hydrogen carbonate (NaHCO3)
Valency of sodium is 1 (Na+)
“ “ HCO3 is 1

First step - Sodium / Bi carbonate.

2nd Step - Na HCO3

3rd Step - Na HCO3

Na (HCO3)

\ The formulae is NaHCO3

ii) Ferrous Sulphate (FeSO4)
Valency of Ferro us is 2 (Fe2+)
Valency of Sulphate is 2 (SO42+)

Ist step ® Ferrous Sulphate
Fe SO4



2nd Step ® Fe2+ SO42
Fe SO4 ® FeSO4

Alluminium nitride ® (Al N)
Valency of Aluminium is 3 (Al3+)
“ “ Nitride is 3 (N3+)
1st Step ® Aluminium nitride

2nd Step ® Al3 N3
3rd Step ® Al3 N3

Al3 N3 ® AlN

iv) Potassium sulphate ® (K2 SO4)

Valency of Potassium is 1 (K+)
“ “ Sulphate is 2 (SO42+)

Ist step ® potassium Sulphate
K SO4

2nd Step ® K

3rd Step ® K SO42

K (SO4) ® K2SO4

18. Write the names of the following compounds.

A. i) (NH4)2 SO4 ® Ammonium Sulphate
ii) Ca (NO3)2 ® Calcium Nitrate
iii) NH4OH ® Ammonium Hydroxide
iv) Na3 PO4 ® Sodium phosphate
v) FeS ® Ferrous sulphide


19. Balance the following equations.
i) Mg + HCl ® MgCl2 + H2
® Magnesium + Hydrochloride acid + Magnesium Chloride + Hydrogen.
® Mg + HCl ® MgCl2 + H2
(Reactants ) (Products)
® Mg + 2 HCl ® Mg Cl2 + H2 ­ (Balanced)

ii) Zn + O2 ® ZnO

® Zinc + Oxygen ® Zinc Oxide
® Zn + O2 ® Zn O
(reactants) (products)
® 2 Zn + O2 + 2 Zn O (Balanced)

iii) NaOH + H2SO4 ® Na2SO4 + H2O

® Sodium hydroxide + Sulphuric acid ® Sodium Sulphate +
Water
® NaOH + H2SO4 ® Na2 SO4 + H2O
(reactants) (products)

® 2 NaOH + 2 H2SO4 ® Na2 SO4 + 2H2O (Balanced)
iv) NaHCo3 ® Na2CO3 + H2O + CO2
Balanced : -2 NaHCO3 ® Na2 CO3 + H2O + CO2
v) Al + S ® Al2S3
2 Al + 3S ® Al2S3 (Balanced)
vi) Ca (OH)2 ®HNO3 ® Ca (NO3)2 + H2O
Ca (OH)2 + 2HNO3 ® Ca (NO3)2 + 2H2O (Balanced)
vii) Na2O + H2O ® NaOH
Na2O + H2O ® 2NaOH (Balanced)
viii) Cu SO4 + 2Ag ® Ag2 SO4 ® Cu (Balanced)
CuSO4 + Ag ® Ag2 SO4 + Cu

20. Draw a neat sketch of the apparatus showing the electrolysis of water and explain.

A. Draw the diagram fig. 3.3 . from SSC book

1. Take a voltameter. It consists of a ‘v’ shaped vessel fitted on a wooden base from the bottom of which rise two platinum Electrodes.
2. The ends of electrodes are connected to brass terminals.
3. Fill half of the voltmeter with water and add to it a few drops of sulphuric acid or salt to make water a good conductor.
4. Insert two graduated tubes completely filled with acidulated water over each of the electrodes.
5. When current passes tiny bubbles of colourless gas collect on each of the electrodes.
6. On testing these gases it is found that gas which collects on – ve electrode is H2 and + ve electrode is Oxygen.
7. The volume of hydrogen and Oxygen gas is in the ratio of 2 : 1 . Further with respect to their weight it is found as 1 : 8.


CHAPTER-2
Air and its Constituents


1. Briefly state the importance of the following constituents of air:
A:- (i) Oxygen:
a)It supports all animals and plant life on the earth, as it is essential for
respiration.
b)It is essential for the combustion of fuels.
c)In nature, it is dissolved in water and is a source of respiration for water
animals.

(ii) Nitrogen:
a)It dilutes the activity of oxygen. Thus, the combustion of fuel during burning
takes place at moderate rate.
b)The compounds of nitrogen are of vital importance to plants as they help the
plants to manufacture proteins.

(iii) Carbondioxide:
a)It acts as food for plants.
b)Carbondioxide dissolved in water, can dissolve rocks containing calcium
carbonate or magnesium carbonate. The rocks, so formed, give taste to natural water.
c)It does not allow the earth to radiate heat energy rapidly at night.

(iv)Water vapour:
a)The presence of water vapour in air determines climatic conditions.
b)The presence of water vapour controls the rate of evaporation from the plants
and animals.
c)The presence of water vapour is very essential for the growth of plants.
d)The presence of water vapour is very essential for health and comfort of
animals.

2. (i)What do you understand by the term polluted air?
A:- When the air contains harmful or undesirable substances, generated by the
activities of man or nature, such that their concentration interferes with human
health or is injurious to plants or animals, it is said to be polluted air.

(ii)State two ways by which air gets polluted in nature.
a)When wind blows hard, it carries dust particles and sand particles in large
amount from one place to another place.
b)When volcanoes erupt, huge amount of ash and sulphur dioxide is added in
the air as pollutants.

(iii)Name and briefly explain four activities of human beings which pollute the air in a big way.
a)Large amount of coal is burnt in thermal plants for generation of electricity
which throw out huge amount of smoke and ash in the atmosphere.
b)Vehicles using petrol or diesel produce large amount of smoke and carbon
monoxide.
c)Burning of wood or coal or kerosene oil produce large amount of
smoke, ash, carbon monoxide, sulphur dioxide and nitrogen oxide.
d)Pesticides spread in the fields also cause air pollution.

(iv)Name and briefly explain four ways by which pollution of air caused by
human beings is minimised.
a)In the houses, we must use improved 'chulha'.
b)In the thermal power plants, cement plants, steel plants, etc., we must provide
electric precipitators, so that smoke and ash entering the atmosphere are
minimised.
c) We must use efficient internal combustion engines in our vehicles, so that
petrol or diesel burns completely without emitting any smoke.
d)We must grow more trees as they are capable of removing harmful gases.

3. Describe your observations, when potassium nitrate crystals are heated strongly
in a test tube and a glowing wooden splint is held near the mouth of test tube.
Write a fully balanced chemical equation for the decomposition of potassium
nitrate.
A:- OBSERVATIONS:
a)The white crystals of potassium nitrate slowly melt to form a colourless liquid.
b)The glowing splint bursts into flame, showing that molten potassium nitrate
gives off oxygen gas.
CHEMICAL EQUATION:
2KNO3 → 2KNO2+O2

4. (i) Starting from hydrogen peroxide, how oxygen gas is prepared in laboratory?
A:- a)Chemicals required:(i)20% hydrogen peroxide solution
(ii)Manganese dioxide.
b) Chemical equation:
2H2 O2→2H2O+O2
Procedure:
(1) Take an absolutely clean and dry conical flask and place in it about 5g of
mangenese dioxide.
2) In the mouth of the flask, fix a two holed stopper. Pass a tap funnel through
one hole and a delivery tube through the other hole, such that other end of the
delivery tube goes into a beehive shelf placed in a trough of water.
3)Pour 20% hydrogen peroxide in the tap funnel and allow it to drip into the
flask drop by drop.
4) Oxygen gas is evolved which is apparent from the bubbles coming out of the
Water trough. Allow the first few bubbles to escape, as they contain air.
5) Place a gas cylinder filled with water in inverted position over the beehive
shelf. The oxygen will collect in the cylinder by the downward displacement
of water.
6) Collect about 8 cylinders of the oxygen gas.

(ii) What is the function of manganese dioxide?
Manganese dioxide accelerates the rate of decomposition of hydrogen
peroxide and acts as a catalyst in the reaction.
(iii) Write a fully balanced equation for the liberation of oxygen from hydrogen
peroxide.

2H2O2 → 2H2O+O2

(iv) Why is the above method preferred to any other method?
a) The oxygen gas is evolved at room temperature. No heating is
required.
b) The rate of evolution of oxygen is fairly fast.
c) Hydrogen peroxide or manganese dioxide are not dangerous chemicals and
hence can be handled easily.

5. State four physical properties of oxygen gas.
A:- a) Colour, odour and taste: Oxygen is a colourless, odourless and tasteless gas.
b) Solubility: Under laboratory conditions, oxygen is practically insoluble in
water. In nature, it slowly dissolves in water.
c)Vapour density: Oxygen is slightly heavier than air.
d) Liquefaction:Under high pressure and low temperature, oxygen can be
changed to liquid state.

6. Describe what will you observe and write fully balanced equations when the
Following are introduced in the jar of oxygen:
A:- (i)Red hot carbon:
when red hot carbon is taken into the cylinder of oxygen, it burns brightly
producing sparkles and a crackling sound.
C + O2 → CO2

(ii)Burning sulphur:
When burning sulphur is taken into the cylinder of oxygen, it burns with a
brilliant blue flame forming sulphur dioxide gas.
S + O2 →SO2

(iii)Burning sodium:
When burning sodium is taken into the cylinder of oxygen, it burns with a
brilliant golden yellow flame to form sodium oxide.
4Na + O2 → 2Na2O

(iv)Burning Magnesium:
When burning magnesium is taken into the cylinder of oxygen, it burns with a
dazzling white flame to form magnesium oxide.
2Mg + O2 → 2MgO

(v)Burning Calcium:
When burning calcium is taken into the cylinder of oxygen, it burns and forms
calcium oxide.
2Ca + O2 → 2CaO

(vi)Burning Phosphorus:
When gently heated phosphorus, is taken into the cylinder of oxygen,it burns
with dazzling white flame producing dense white fumes of phosphorus
pentoxide.
4P + 5O2 → 2P2O5

7. (i)State three uses of oxygen, other than artificial respiration.
A:- a)Liquid oxygen(LOX) is used for burning fuel in the rockets and space-ships as
there is no air in the space.
b) Oxygen is used in large amount for preparing sulphuric acid from sulphur and
nitric acid from ammonia.
c) During mining, large amount of explosives are required. Cartridges made of
one part of coal dust, one part of petroleum jelly and eight parts of liquid
oxygen are used for blasting rocks.
(ii) Give two tests for oxygen.
a) It rekindles glowing wooden splinter.
b) If mixed with colourless nitric oxide gas,it forms reddish brown fumes of
nitrogen dioxide.

8. (i)What is rust?
A:- The hydrated oxide of iron is called rust.

(ii)State two most important conditions for rusting.
a)There must be air.
b)The air should be moist.

(iii)State four ways of preventing rusting.
The four ways of preventing rusting are :-
a)By coating with red lead oxide paint or tar.
b)By painting with enamel paints.
c)By enamelling.
d)By galvanising.

9. Write chemical equations for the preparation of carbon dioxide from the
following:
A:- (i)Only calcium carbonate.
CaCO3 → CaO + CO2

(ii)Only sodium hydrogen carbonate.
2NaHCO3 → Na2CO3 + H2O + CO2

(iii)Sodium hydrogen carbonate and acetic acid.
NaHCO3 + CH3COOH → CH3COONa + H2O + CO2

(iv)Sodium carbonate and dilute sulphuric acid.
Na2CO3 + H2SO4(dil) → Na2SO4 + H2O + CO2

10. Draw a neat and fully labelled diagram for the preparation of carbondioxide gas
in laboratory.
A:- Refer fig.2.21 of page 35 from reader.

11. What is dry ice? State two uses of dry ice.
A:- Solid carbon dioxide is called dry ice.
USES:
Dry ice is used as a refrigerant for shipping perishable food materials such as
meat, fish, fruit and vegetables over long distances.

12. Briefly state four uses of carbon dioxide gas.
A:- (i)When carbon dioxide gas, under a pressure of 20 atmospheres, is passed
through water, it rapidly dissolves in water to form plain soda or soda water
and it is also used to prepare soft drinks.
(ii)When food grains are kept in the atmosphere of carbon dioxide, it prevents
the grains from destruction by insects.
(iii) Carbon dioxide is used in large amounts in the manufacture of industrial
chemicals, such as washing soda, baking soda and white lead.
(iv) Solid carbon dioxide is used as a refrigerant for shipping perishable food
materials such as meat, fish, fruit and vegetables over long distances.

13. How will you test the presence of carbon dioxide gas?
A:- TESTS OF CARBON DIOXIDE GAS:
a) If a burning match stick or a candle is taken in the jar of carbondioxide,it gets extinguished.
b) It turns clear lime water milky.



Chapter – 3
Chemistry in your Life

1. i) What do you understand by the term metal?
A. Metals : The elements, which are generally hard solids, have lustre and are malleable, ductile, tensile and good conductors of heat and electricity , are called metals.

ii) State any five physical properties of a metal.
A. 1)State : Metals are generally solid at room temperature. They change into vapours at very high temperature.
2) Lustre : When metals are freshly cut, they have a brilliant shine over the cut surface. This metallic shine is called lustre.
3) Density : Metals generally have high density.
4) Melting and boiling points: Metals generally have high melting
and boiling points.
5) Conductivity : Metals in general are good conductors of heat and electricity.

2. i) State any metal which is liquid at room temperature.
A. Mercury

ii) Name a metal which can be cut with a knife.
A. Sodium.

iii) Name a metal which is lighter than water.
A. Potassium

iv) Name a metal which is not malleable.
A. Zinc.

v) Name a metal which is the best conductor of heat and electricity
A. Silver

3. State two important uses of the following metals
1) Gold : i) It is used for making jewellery
ii) It is used for making coins of high value.
2) Silver : i) It is used for making coins and ornaments.
ii) It is used for making table cutlery.
A. 3) Copper : i) It is used for making electric transmission wires.
ii) It is used for making utensils.
4) Iron : i) It is used in the construction of sailing ships.
ii) It is used in the construction of buildings.

5) Tin : i) It is used for tinning food cans and the cooking vessels made from copper or iron.
ii) It is used for making alloys, such as brass and bronze.

6) Lead : i) It is used for making lead acid batteries used in all kinds of automobiles.
ii) It is used for making sanitary pipes.

7) Zinc : i) It is used as negative electrode of dry cells.
ii) it is used for making alloys, such as brass and bronze.

8) Aluminium: i) Aluminium foils are used for packing food materials, medicines, etc.
ii) It is used for making alloys like duralumin and magnalium which are very light and almost as tough as steel.
9)Magnesium : i) It burns with a dazzling white flame and hence is used in fire works.
ii) It is used in the making of alloys, such as magnalium
10) Mercury : i) It is used as a thermometric liquid.
ii) Gold amalgam and silver amalgam are used in dentistry for filling tooth cavities.

4. i) What do you understand by the term non metals?
A. Non metals are elements which are either gases or soft solids, have no lustre, and are non – malleable, non- ductile, brittle and bad conductors of heat and electricity.

ii) State any five physical properties of a non metals.
A. 1) State : Non – metals are generally gases at room temperature. Bromine is a liquid at room temperature.

2) Lustre : None – metals do not have lustre.
Exception : Graphite, iodine
3) Density : Non- metals generally have a low density.
Exception: Carbon, sulphur, phosphorus
4) Melting point and boiling points: Non – metals have generally low melting and boiling points.
5) Malleability : Non – metals are non- malleable, i.e., they cannot be drawn into sheets.

5. i) Name the form of a non-metal which is hardest and naturally occurring substance.
A. Diamond

ii) Name a non-metal which is liquid at room temperature.
A. Bromine
iii) Name the form of a non-metal which is good conductor of electricity.
A. Graphite
iv) Name a non-metal which is greenish yellow gas.
A. Chlorine

v) Name a non-metal which helps in the growth of plants.
A. Nitrogen.

6. Give two uses of the following i) Common salt ii) Hydrocholric acid
A. i) Common Salt :
1) It is used in the preservation of meat and fish.
2) It is used in the manufacture of important chemicals such as baking soda, washing soda, hydrochloric acid, caustic soda and chlorine.

ii) Hydrochloric acid : i) It is used in the preparation of silver chloride, which is used in the manufacture of photographic printing paper.
ii) It is used in making bathroom cleansing agents.

7. i) What are fertillisers ?
A. The material added to the soils, so as to make up for the deficiency of essential nutrients are called fertilizers.

ii) Name a) three nitrogenous fertillisers b) two phosphatic fertilizers c) two potash fertilizers.

A. a) Nitrogenous fertilizers : Calcium ammonium nitrate, basic calcium nitrate, ammonium sulphate and urea .
b) Phosphatic fertilizers: Triammonium phosphate and super phosphate of lime.
c) Potash Fertilisers : Potassium chloride , potassium nitrate

8. State the use/uses of the following substances:
A. i) Sand is used in the manufacture of glass and cement.
ii) Sodium silicate is used in the preservation of eggs.
iii) Silicons are used in the preparation of waterproof clothes, non stick pans, polishing waxes, and insulating materials for electrical appliances.
iv) Blue vitriol is a pesticide. It is used for spraying over citrus trees and grapevines so as to kill insects.
v) Limestone is used as mortar in the construction of buildings, white washing, in the manufacture of cement and glass for making flooring and statues as well as monuments.
vi) Gypsum which is converted into Plaster of Paris by heating it to
1000C is used to reduce the acidity of soil.
vii) Plaster of Paris is utilized to keep the fractured bones in fixed position, is used for paneling ceilings of big halls.
It is used for making black board chalk.

9 Name three organic classes of compounds which are essential for human beings.
A. i) Carbohydrates, Fats, proteins.
ii) Methane an organic gas which is used as fuel.

10. State three major uses of cement.
A. i) Pure cement is used for grouting.
ii) It is used for joining bricks and plastering.
iii) Cement concrete is used for making floors of any kind of dwellings.

11. Give one use of the following kinds of glass: i) Soda glass ii) Hard glass iii) Optical glass iv) Borosil glass.
A. i)Soda glass : It is used for making window panes, glass bottles and glass tumblers and cheap articles of glass.
ii) Hard glass : It is used for making laboratory apparatus.
iii)Optical glass : It is used for making lenses for spectacles, and optical instruments,
iv) Borosil glass: It is used for making laboratory apparatus, coffee flasks, baking bowls, etc.

12. What do you understand by the following term i) Plastic
ii) Plasticity iii) Polymer

A. i) Plastic: Plastic is a man-made material made by the polymerization of simple molecules such as ethane, vinyl chloride, etc.
ii) Plasticity : The property by virtue of which a substance can be moulded into various forms is called plasticity.
iii) Polymers: Polymers are molecules of same substance, joined together to form a chain or a bigger molecule.

13. State four characteristics of plastics.
A. i) Chemical resistance : Where all other materials such as wood, metals, ceramics, etc., are easily attacked by strong chemicals, there is hardly any effect on plastics.
ii) Weather resistance : Plastics are not biodegradable.
iii) Lightweight : Plastic materials weight far less compared to materials made from metals, wood, ceramics or glass.
iv) Toughness : Plastic materials can withstand hammering without getting broken.

14. By giving atleast three examples, explain clearly, what do you understand by the following terms:
A. i)Thermoplastics:
A. Thermoplastic is a kind of plastic which can be remoulded into any desired shape by gentle heating. Polyvinyl chloride, polyethene, polystyrene, nylon and terelyene are examples of thermoplastic.

ii) Thermo setting plastic:
A. Thermosetting plastic is a kind of plastic which can be moulded into any desired shape on heating, but the article so formed cannot be remoulded further. Bakelite, urea, formaldehyde, polyurethane, melamine are examples of thermosetting plastic.

15. i) What is soap? Name the raw materials for the preparation of
soap.
A. Soap is a sodium salt of fatty acids formed by the chemical reaction between sodium hydroxide and vegetable oils or fats.

ii) What is synthetic detergent? Name the raw materials for its preparation.
A. Detergent is synthetic cleansing agent, which is chemically sodium lauryl sulphate.

iii) What is the advantage of detergent over soap?
A. Synthetic detergents lathers even in the hard water, whereas the soap does not.

CHAPTER-4
Acids, bases and Salts
­­­­­­­­­­­­­­­­
What do you understand by the term acid? Support your answer by giving one example, along with an equation for
i) Mono basic acid ii) Dibasic acid iii) Tribasic acid .
A. A substance which dissolves in water to furnish H+ ions as the only positively charged ions is called an acid.
Ex : Hydro Chloric acid
i) Mono Basic Acid :
Hydrochloric acid

HCl H+ + Cl-
ii) Dibasic Acid:
Sulphuric acid :

H2SO4 2H+ +
iii) Tribasic Acid:
Prosphoric acid :
H3PO4 3H+ +

2. Classify the following acids as organic acids and inorganic acids:
A. i) Acetic acid – Organic acid
ii) Carbonic acid – Inorganic acid
iii) Nitric acid - Inorganic acid
iv) Lactic acid- Organic acid
v) Sulphuric acid – Inorganic acid
vi) Nitrous acid- Inorganic acid
vii) Oleic acid - Organic acid
viii) Hydro Chloric acid- Inorganic acid
ix) Citric acid – Organic acid
x) Tartaric acid – organic acid

3. What do you understand by the term i) Strong acid ii) weak acid ? support your
answer with two examples.
A. i) Strong acid : The acids in which more than 30% of the molecules of it ionise in water to furnish H+ ions are called strong acids.
Ex : Sulphuric acid, Hydro chloric acid.
ii) Weak acid : The acids in which less than 30% of the molecules of it ionise in water to furnish H+ ions are called weak acids.
Ex: Carbonic acid, Sulphurous acid .
4. Complete the equations given below.
A. i) C + O2 ® CO2
ii) SO2 + H2O ® H2SO3
iii) Mg + HCl ® MgCl2 + H2
iv) ZnO + 2HCl ® ZnCl2 + H2O
v) 2NaOH + H2SO4 ® Na2SO4 + 2H2O
vi) MgCO3 + 2HCl ® Mg Cl2 + H2O + CO2

5. State two uses of the following acids. i) Sulphuric acid ii) hydrochloric acid iii) nitric acid
A. i) Sulphuric acid :
a) It is used in the manufacture of fertilisers.
b) It is used in car batteries.

ii) Hydro chloric acid:
a) It is used in dyeing industry.
b) It is used for preparing glucose from starch.

iii) Nitric acid:
a) It is used in the manufacture of fertilisers such as ammonium nitrate and calcium ammonium nitrate.
b) It is used in the manufacture of explosives such as TNT(trinitrotoluene) and
TNG(trinitroglycerine).

6. i) What do you understand by the term base?
A. The substances which react with acids to form salt and water as the only products
are called bases.

ii) What is the difference between a base and an alkali?
The substances which react with acids to form salt and water as the only products
are called bases and all the bases which are soluble in water are called alkalies.

iii)Give examples of a) Strong alkalies
b)Weak alkalies
a) Strong alkalies: Sodium hydroxide, Potassium hydroxide.
b) Weak alkalies: Calcium hydroxide,Ammonium hydroxide.

7. State three uses of:
A. i)Caustic soda:
a) They are extensively used in the manufacture of soap from vegetable oils.
b) They are used in paper industry for preparing paper pulp from wood.
c) They are used for making artificial fibres such as rayon, nylon, etc.

ii) Calcium hydroxide:
a) Calcium hydroxide suspension is used in white washing.
b) Calcium hydroxide is used for making mortar, which is used in the construction of buildings.
c) Calcium hydroxide is used for removing hair from the animal skins.
8. By giving two examples, define the following:
A. i) Normal salts:
The salts formed by the complete replacement of the hydrogen ions(H+) of an acid with metal ions (or positively charged ions) are called normal salts.
Ex:-Sodium chloride, Sodium nitrate
ii)Acid Salts:
The salts formed by the partial replacement of H+ ions of an acid from its
molecule, with metal ions, are called acid salts.
Ex:- Sodium hydrogen sulphate, Sodium hydrogen carbonate.

iii) Basic salts:
The salts formed by the partial neutralization of hydroxyl ions(OH-) of a base, by
an acid are called basic salts.
Ex:- Zinc hydroxy chloride, Copper hydroxy chloride.

iv) Hydrated salts:
The salts which contain certain fixed number of water molecules, attached loosely
to their one molecule, are called hydrated salts.
Ex:- Copper sulphate, Iron sulphate.

v) Anhydrous salt:
The residue left when a hydrated salt loses its water of crystallization, is called
anhydrous salt.
Ex:- Copper sulphate, Zinc sulphate.

vi) Deliquescent salts:
The salts which change into solution form due to the absorption of water from air,
are called deliquescent salts.
Ex:- Calcium chloride, Magnesium chloride.

CHAPTER – 5
Water

­­­­­­­­­­­­­­­Give two examples of i) Underground water ii) Surface water.
i) Underground water: Well water, Spring water.
ii) Surface water: Rain water, Sea water.

Briefly describe the water cycle in nature.
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, commonly called clouds.
when the clouds contain too much of water, they cause rain. The rain water flows over the surface of Earth in the form of streams and rivers. Some amount of rain
water collects within the earth in the form of sub-soil water. Ultimately, the water
is absorbed by the soil or flowing water of surface reaches the sea through rivers.
Thus, a natural balance is built, i.e., the amount of water which vaporizes is equal
to amount of water which returns to earth in the form of rain.

3. i) What is potable water?
A. The water fit for human consumption is called potable water.
ii) Why is distilled water not potable?
If we drink distilled water, it will dissolve essential salts present in our body. This may lead to deficiency of vital salts which in turn can make us sick.
iii) State three chief qualities of the potable water.
a) It must be clear and colourless.
b) It must be odourless.
c) It must be free from harmful bacteria and suspended impurities.
4. i) What do you understand by the following terms?
A. a) Soft water : A sample of ground water which freely lathers with soap solution, is called soft water.
b) Hard water : A sample of ground water, which instead of freely forming lather with soap solution, forms sticky scum (or precipitate), is called hard water.
c) Temporary hard water: A sample of ground water which ordinarily forms scum with soap solution, but on boiling and then treating with soap solution forms
lather, is called temporary hard water.
d)Permanent hard water: A sample of ground water which even on boiling
and then treating with soap solution does not lather but forms a scum, is
permanent hard water.

ii) a)Name two chemicals which are responsible for temporary hardness of water.
Calcium hydrogen carbonate and magnesium hydrogen carbonate.
b) Name four chemicals which are responsible for permanent hardness of water.
Calcium chloride, magnesium chloride, Calcium sulphate and magnesium
sulphate.

5. How does water get temporarily hard in nature?
A. When the rain water flows over the surface of the earth, it dissolves in it carbon dioxide gas present in the air. When the water containing carbon dioxide flows over the rocks containing calcium carbonate or magnesium carbonate, it reacts with them to form their respective hydrogen carbonates and, hence, the water becomes temporary hard.

6. How can you remove the following in case of water?
A. i) Temporary hardness : When the temporary hard water is boiled, the hydrogen carbonates of calcium or magnesium decompose to form their respective insoluble carbonates, which can be filtered out and the water becomes soft.
ii) Permanent hardness: Permanent hardness can be removed by treating the water with sodium carbonate. It reacts with chlorides or sulphates of calcium or magnesium to form their respective insoluble carbonates, which can be filtered out and water becomes soft.

7. i) Briefly explain how ground water gets polluted by defecation of humans and
animals?
A. In most parts 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. In many places, raw excreta is directly dumped in rivers. The sewer – water of big cities is also discharged in the rivers directly. This highly pollutes water.
ii) How the pollution in 7 (i) can be minimized?
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 cow dung should be converted into biogas in biogas plants. This gas can be used for cooking and illumination purposes, where as slurry left is a rich natural manure. It can be used for fertilising fields. The sewer –water in big cities should be treated properly, and all harmful substances should be removed from it, before discharging it in the rivers.

8. State five physical properties of water.
A. i) It is a colourless, tasteless and odourless.
ii) Melting point of water is 00 C.
iii) Boiling point of water is 1000 C.
iv) Density of water is 1 gm/cc.
v) It is a universal solvent.


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