1. Give an example of a metal which
(i) Is a liquid at room temperature?
(ii) Can be easily cut with a knife?
(iii) Is the best conductor of heat?
(iv) Is a poor conductor of heat?
Solution:
(i) Mercury is the metal which is liquid at
room temperature
(ii) Sodium and potassium are the metals
which can be cut with a knife
(iii) Silver is the best conductor of heat
(iv) Mercury and lead are poor conductor of
heat.
2. Explain the meanings of malleable and
ductile.
Solution:
Metals which can be beaten to sheets are said
to be malleable
Metals which can be drawn into thin wires are
said to be ductile
In-text questions set 2 Page number 46
1. Why is sodium kept immersed in kerosene
oil?
Solution: Sodium is a reactive metals,
if kept open it will react with oxygen to explore and catch fire. Sodium metal
is kept immersed in kerosene to prevent their reaction with oxygen, moisture
and carbon dioxide of air.
2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Solution: (i) Iron reacts with steam to
form a magnetic oxide of Fe with the liberation of H2.
3Fe(s) + 4H2O(g) → Fe3O4(s)
+ 4H2(g)
(ii) Calcium reacts with water to form
calcium hydroxide and hydrogen.
Ca(s) + 2H2O(I) → Ca(OH)2(aq)
+ H2(g)
Potassium reacts with cold water violently
immediately with evolution of H2 which catches fire.
2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)
3. Samples of four metals A, B, C and D were
taken and added to the following solution one by one. The results obtained have
been tabulated as follows
|
Metal |
Iron(II) sulphate |
Copper(II) sulphate |
Zinc sulphate |
Silver Nitrate |
|
A |
No reaction |
Displacement |
– |
– |
|
B |
Displacement |
– |
– |
– |
|
C |
No reaction |
No reaction |
No reaction |
Displacement |
|
D |
No reaction |
No reaction |
No reaction |
No reaction |
Use the Table above to answer the following
questions about metals A, B, C and D.
Which is the most reactive metal?
What would you observe if B is added to a
solution of Copper (II) sulphate?
Arrange the metals A, B, C and D in the order
of decreasing reactivity.
Solution:
(i) Metal B is the most reactive as it gives
displacement reaction with iron (II) sulphate.
(ii) When metal B is added to copper (II)
sulphate solution, a displacement reaction will take place because of which the
blue colour of copper (II) sulphate solution will fade and a red-brown deposit
of copper will be formed on metal B.
(iii)Metal B is the most reactive because it
displaces iron from its salt solution. Metal A is less reactive because it
displaces copper from its salt solution. Metal C is still less reactive because
it can displace only silver from its salt solution and metal D is the least
reactive because it cannot displace any metal from its salt solution. Hence,
the decreasing order of reactivity of the metals is B > A > C > D.
4. Which gas is produced when dilute
hydrochloric acid is added to a reactive metal? Write the chemical reaction
when iron reacts with dilute H2SO4.
Solution: Hydrogen gas is liberated when
dilute HCl is added to a reactive metal.
Fe(s) + H2SO4(aq) →
FeSO4(aq) + H2(g)
5. What would you observe when zinc is added
to a solution of iron (II) sulphate? Write the chemical reaction that takes
place.
Solution: Zinc is more reactive (more
electro positive) than iron. Therefore Zinc displaces Iron from its salt
solution. The colour of ferrous sulphate is pale green, which turns colourless.
FeSO4 + Zn → ZnSO4 +
Fe(s)
Light green Zinc
sulphate(Colourless)
In-text questions set 3 Page number 49
1. (i) Write the electron-dot structures for
sodium and oxygen.
(ii) Show the formation of Na2O
and MgO by the transfer of electrons.
(iii)What are the ions present in these compounds?
Solution: (i) Sodium:
Oxygen:
(ii) Formation of Magnesium oxide:
When magnesium reacts with oxygen, the
magnesium atom transfers its two outermost electrons to an oxygen atom. By
losing two electrons, the magnesium atoms form a magnesium ion (Mg2+)
and by gaining two electrons, the oxygen atom forms an oxide ion (O2-).
Mg: + ::O:: à MgO
Formation of Sodium oxide:
Two sodium
atoms transfer their 2 outermost electrons to an oxygen atom. By losing two
electrons, the two sodium atoms form sodium ions (2Na+).
And by gaining two electrons, the oxygen atom forms an oxide ion (O2-).
Na.
+:O:: à Na2O
Na.
(iii) The
ions present in sodium oxide compound (Na2O) are sodium ions (2Na+)
and oxide ions (O2-).
The ions
present in Magnesium oxide compound (MgO) are magnesium ions Mg2+ and oxide ions (O2-).
2.
Why do ionic compounds have high melting points?
Solution: Ionic compounds are the ones which has
both positive and negative charges. Hence there will be strong force of
attraction between them. This make expenditure of lot of heat to break this force
of attraction hence ionic compounds have high melting points.
In-text
questions set 4 Page number 53
1.
Define the following terms.
(i)
Mineral
(ii)
Ore
(iii)
Gangue
Solution:
Minerals are
compounds (also known as elements) which are found naturally in the earth’s
crust. E.g. Alums, K2SO4.Al2(SO4)3.24H2O, etc.
Ores are
minerals from which metal can be extracted Ex: Bauxite Al2O3.2H2O is the ore of Al,
copper pyrite CuFeS2.All
minerals are not considered as ores but all ores are also minerals.
Ores mined
from the earth are naturally contaminated with sand, rocky materials. There are
impurities present in the ore which are known as gangue.
2.
Name two metals which are found in nature in the free state
Solution: Gold and platinum are the two metals found in
Free State in nature.
3.
What chemical process is used for obtaining a metal from its oxide?
Reduction
method is used to obtain metal from its oxide. Ex: Zinc oxide is reduced to
metallic zinc by Heating with carbon.
ZnO + C → Zn
+ CO
Ex: Lead
oxide is reduced to lead by heating with carbon
PbO +C → Pb
+ CO
In-text
questions set 5 Page number 55
1.
Metallic oxides of zinc, magnesium and copper were heated with the following
metals.
|
Metal |
Zinc |
Magnesium |
Copper |
|
Zinc Oxide |
|||
|
Magnesium Oxide |
|||
|
Copper Oxide |
Solution:
A more
reactive metal can displace a less reactive metal from its oxide. Among Zinc,
Magnesium, and Copper metals, magnesium is the most reactive, copper is the
least reactive metal and zinc is less reactive .The displacement reaction will
take place in the following cases
|
Metal |
Zinc |
Magnesium |
Copper |
|
Zinc Oxide |
– |
Displacement |
– |
|
Magnesium Oxide |
– |
– |
– |
|
Copper Oxide |
Displacement |
Displacement |
– |
2.
Which metals do not corrode easily?
Solution: Gold and platinum are the metals which do not
corrode easily
3.
What are alloys?
Solution: An alloy is a homogeneous mixture of
two or more metals, or a metal and a non-metal.
Exercise
questions Page number 56-57
1.
Which of the following pairs will give displacement reactions?
(a)
NaCl solution and copper metal
(b)
MgCl2 solution
and aluminium metal
(c)
FeSO4 solution
and silver metal
(d)
AgNO3 solution
and copper metal
Solution: Option d i.e AgNO3 solution and copper is correct answer. Copper
displace the silver cations (reducing them to the elemental metal), in the
process copper itself being oxidised to Copper II cations (Cu2+) and going into solution. So silver
metal precipitating out and a copper II nitrate solution will be remaining.
Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)
2.
Which of the following methods is suitable for preventing an iron frying pan
from rusting?
Applying
grease
Applying
paint
Applying
a coating of zinc
All
of the above
Solution: Answer is (c) Applying a coat of Zinc
Though
applying grease and applying paint prevents iron from rusting but we cannot
apply these methods on frying pan hence applying a coat of Zinc is most
appropriate method to prevent an iron pan from rusting.
3.
An element reacts with oxygen to give a compound with a high melting point.
This compound is also soluble in water. The element is likely to be
(a)
Calcium
(b)
Carbon
(c)
Silicon
(d)
Iron
Solution: Correct answer is option (a) i.e Calcium.
Calcium
reacts with oxygen to give calcium oxide. Calcium oxide is soluble in water to
give Calcium Hydroxide.
Carbon forms
carbon-oxide with oxygen which is gas hence option B is wrong
Silicon
reacts with oxygen and forms silicon dioxide. This is insoluble in water. So
option C is not correct.
Iron reacts
with oxygen and forms Iron dioxide. This is insoluble in water. So option D is
not correct.
4.
Food cans are coated with tin and not with zinc because
(a)
Zinc is costlier than tin.
(b)
Zinc has a higher melting point than tin.
(c)
Zinc is more reactive than tin.
(d)
Zinc is less reactive than tin.
Solution: Answer is c. Food cans are coated with tin
and not with zinc because Zinc is more reactive that is electro positive than
tin.
5.
You are given a hammer, a battery, a bulb, wires and a switch.
(a)
How could you use them to distinguish between samples of metals and non-metals?
(b)
Assess the usefulness of these tests in distinguishing between metals and
non-metals.
Solution:
Metals are
malleable and can be easily drown into sheets by hitting with hammer. On the
other hand if we beat non-metals they break down and they cannot be drawn into
sheets as they are non-malleable. Metals of good conductors of electricity
hence they make bulb when you connect metals with a battery, wire and bulb.
Similarly If non-metals are bad conductors of electricity chance they fail to
lit up the bulb on connecting with wire and battery.
These
experiments can be helpful to demonstrate the malleability and electric
conductivity of the metals and non-metals
6.
What are amphoteric oxides? Give two examples of amphoteric oxides
Solution: Oxides that react with both acids and bases
to form salt and water are known as amphoteric oxides. Examples: PbO and
Al2O3.
Amphoteric
oxides are the one which reacts with both acids and bases to form salt and
water. Examples: Lead oxide – PbO and Aluminium oxide – Al2O3.
7.
Name two metals which will displace hydrogen from dilute acids, and two metals
which will not.
Solution: Zinc (Zn) and Magnesium (Mg) are the two
metals which will displace Hydrogen from dilute acids as they are very reactive
metals. Gold (Au) and Silver (Ag) are the metals which will not replace
Hydrogen from dilute acids as these metals are less reactive.
8.
In the electrolytic refining of a metal M, what would you take as the anode,
the cathode and the electrolyte?
Solution: In the process of electrolytic refining of
metal called ‘M’, An impure and thick block of metal M. is considered as anode,
Thin strip or wire of pure metal M is taken as cathode. A suitable salt solution
of metal M is considered as the electrolyte.
9.
Pratyush took sulphur powder on a spatula and heated it. He collected the gas
evolved by inverting a test tube over it, as shown in figure below.
(a)
What will be the action of gas on
(i)
dry litmus paper?
(ii)
moist litmus paper?
(b)
Write a balanced chemical equation for the reaction taking place.
Solution:
a) When sulphur
powder is burnt in the air sulphur-di-oxide is formed.
(i)
Sulphur-di-oxide does not have any effect on dry litmus paper.
(ii)
Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to
sulfurous acid.
(b) S(s) + O2(g) → SO2(g)
SO2(g) + H2O →H2SO3
10.
State two ways to prevent the rusting of iron.
Solution:
Iron can be
prevented from rusting by coating the surface of the iron with rust proof
paints
By applying
Oil/grease on the surface of iron objects as it will prevent the iron surface
to get in contact with air consisting of moisture.
11.
What type of oxides are formed when non-metals combine with oxygen?
Solution: When non-metals combine with oxygen it forms
either acidic or neutral oxides. Ex: N2O5 or
N2O3 is an acidic oxide;
CO is a neutral oxide.
12.
Give reasons
(a)
Platinum, gold and silver are used to make jewellery.
(b)
Sodium, potassium and lithium are stored under oil.
(c)
Aluminium is a highly reactive metal, yet it is used to make utensils for
cooking.
(d)
Carbonate and sulphide ores are usually converted into oxides during the
process of extraction
Solution:
(a)
Platinum, gold and silver are used to make jewellery for these metals are very
less reactive hence they are not affected by air, water or most chemicals.
These metals have a lot of luster and they are malleable and ductile in nature
and also high corrosion resistance in nature.
(b) Sodium,
potassium and lithium readily react with water to produce a lot of heat. As a
result, Hydrogen evolved in the reaction results in a fire. On exposure to
water they react with moisture (water droplets) present in the atmosphere, In
order to prevent contact with water hence these metals are stored under oil.
(c)
Aluminium forms on its surface a nonreactive surface of aluminium oxide. Such
coating prevents other compounds from reacting to aluminium. So aluminium is
being used to produce utensils for cooking.
(d) Reducing
metal oxide into free metal is easy. Additionally, because it is easier to
obtain metals directly from their oxides than from their carbonates or
sulphides, the carbonate and sulphide ores are first transformed to oxides to
obtain the metals.
13.
You must have seen tarnished copper vessels being cleaned with lemon or
tamarind juice. Explain why these sour substances are effective in cleaning the
vessels.
Solution: Tarnished copper vessels being cleaned with
lemon or tamarind because this sour substance contains acids which dissolve the
coating of copper oxide or basic copper carbonate present on the surface or
tarnished copper vessels. This makes them shining red-brown again. Hence they
are very effective in cleaning tarnished copper vessels.
14.
Differentiate between metal and non-metal on the basis of their chemical
properties.
Solution:
|
Metals |
Non-metals |
|
When metals are heated with
oxygen, they form ionic oxides which are basic in nature and form bases on
dissolving with water. This turn red litmus paper to blue. |
When non-Metals are heated with
oxygen, they form covalent oxides which are acidic in nature which form acid
on dissolving with water. This turn blue litmus paper to red. |
|
They are electro positive, lose
electrons readily and become a positive ion. |
They are electro negative, gain
electrons and become negative ions. |
|
Metals are lustrous. |
Non-metals are non-lustrous;
graphite is the exception |
|
Reducing agents. |
Good oxidizing agents. |
|
Metals are the good conductors
of electricity and heat. |
Non-metals are non-conductors
of electricity and heat; graphite is the exception |
|
All metals are solids except
mercury. |
Non-metals are in solid-liquid
and gaseous states |
15.
A man went door to door posing as a goldsmith. He promised to bring back the
glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold
bangles to him which he dipped in a particular solution. The bangles sparkled
like new but their weight was reduced drastically. The lady was upset but after
a futile argument the man beat a hasty retreat. Can you play the detective to
find out the nature of the solution he had used?
Solution: Goldsmith used the solution called Aqua regia
which is called as royal water in Latin. It is the mixture of concentrated
Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia
is capable of dissolving noble metals like gold and platinum. When upper-layer
of dull gold ornament is dissolved they lose their weight.
16.
Give reasons why copper is used to make hot water tanks and not steel (an alloy
of iron).
Solution: Copper is used to make hot water tanks and
not steel (an alloy of iron) because copper does not reacts with either water
or steam whereas iron reacts with steams to corrode the tank.
Elements can
be categorised into two types viz, Non-Metals
and Metals. Excluding
mercury, all metals are solid at room temperature. Some other important
properties of metals include
They are
malleable
Lustrous
Good
conductors of electricity and heat
They lose
their electrons to form positively charged ions
They form
basic oxides by combining with oxygen
What are
amphoteric oxides?
Oxides which
show basic and acidic properties are called amphoteric oxides. Examples are,
zinc oxide and aluminium oxide.
What is
metallurgy?
The process
of extracting metal from ore and refining it is called metallurgy.
What is
corrosion?
Corrosion is
a phenomenon where a metal like iron is exposed to moistened air for a long
period.
What are
non-metals?
Non-metals
are not ductile and malleable. Excluding graphite, all non-metals are bad
conductors of electricity and heat. They gain electrons to form negative ions
when they react with metals. Non-metals form hydrides by reacting with
hydrogen. They can form oxides which are either neutral or acidic.
