Question 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.
Answer:
(i) Metal
that exists in liquid state at room temperature →
Mercury
(ii) Metal
that can be easily cut with a knife →
Sodium
(iii) Metal
that is the best conductor of heat →
Silver
(iv) Metals
that are poor conductors of heat →
Mercury and lead
Question 2:
Explain
the meanings of malleable and ductile.
Answer:
Malleable:
Substances that can be beaten into thin sheets are called malleable.
For example, most of the metals are malleable.
Ductile:
Substances that can be drawn into thin wires are called ductile. For
example, most of the metals are ductile.
Question 1:
Why is sodium kept immersed in kerosene oil?
Answer:
Sodium and potassium are very reactive metals and and combine explosively with air as well as water. Hence, they catch fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored in kerosene oil.
Question 2:
Write equations for the reactions of
(i) iron
with steam
(ii) calcium
and potassium with water
Answer:
Question 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
|
Cooper (II) sulphate
|
Zinc sulphate
|
Silver nitrate
|
|
A.
|
No reaction
|
Displacement
|
|
|
|
B.
|
Displacement
|
|
No reaction
|
|
|
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.
(i) Which
is the most reactive metal?
(ii) What
would you observe if B is added to a solution of copper (II)
sulphate?
(iii) Arrange
the metals A, B, C and D in the order of decreasing reactivity.
Answer:
Explanation
A +
FeSO4
→
No reaction, i.e., A is less reactive than iron
A +
CuSO4
→
Displacement, i.e., A is more reactive than copper
B +
FeSO4
→
Displacement, i.e., B is more reactive than iron
B +
ZnSO4
→
No reaction, i.e., B is less reactive than zinc
C +
FeSO4
→
No reaction, i.e., C is less reactive than iron
C +
CuSO4
→
No reaction, i.e., C is less reactive than copper
C +
ZnSO4
→
No reaction, i.e., C is less reactive than zinc
C +
AgNO3
→
Displacement, i.e., C is more reactive than silver
D +
FeSO4/CuSO4/ZnSO4/AgNO3
→
No reaction, i.e., D is less reactive than iron, copper, zinc, and
silver
From
the above equations, we obtain:
(i) B is
the most reactive metal.
(ii) If B is added to a solution of copper (II)
sulphate, then it would displace copper.
B
+ CuSO4
→
Displacement
(iii) The arrangement of the metals in the order
of decreasing reactivity is:
B > A > C > D
Question 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.
Answer:
Hydrogen gas is evolved when dilute hydrochloric acid is added to a
reactive metal.
When
iron reacts with dilute H2SO4,
iron (II) sulphate with the evolution of hydrogen gas is formed.
Question 5:
What would
you observe when zinc is added to a solution of iron (II) sulphate?
Write the chemical reaction that takes place.
Answer:
Zinc is
more reactive than iron. Therefore, if zinc is added to a solution of
iron (II) sulphate, then it would displace iron from the solution.
Question 1:
(i) Write the electron-dot structures for sodium, oxygen and
magnesium.
(ii) Show the formation of Na
2O and MgO by the transfer
of electrons.
(iii) What are the ions present in these compounds?
Answer:
(i) The representation of elements with valence electrons as dots
around the elements is referred to as electron-dot structure for
elements.

(ii)

(iii) The ions present in Na
2O are Na
+ and
O
2− ions and in MgO are Mg
2+ and O
2−
ions.
Question 2:
Why do ionic compounds have high melting points?
Answer:
Ionic compounds have strong electrostatic forces of attraction
between the ions. Therefore, it requires a lot of energy to overcome
these forces. That is why ionic compounds have high melting points.
Question 1
Define the
following terms.
(i) Mineral
(ii) Ore (iii) Gangue
Answer:
(i) Mineral: Most of the
elements occur in nature as in combined state as minerals. The
chemical composition of minerals is fixed.
(ii) Ore: Minerals from
which metals can be extracted profitably are known as ores.
(iii) Gangue: The impurities (sand, silt, soil,
gravel, etc.) present in the ore are called gangue.
Question 2:
Name two metals which are found in nature in the free state.
Answer:
The
metals at the bottom of the reactivity
series are mostly found in free state. For example: gold, silver, and
platinum.
Question 3:
What chemical process is used for obtaining a metal from its oxide?
Answer:
The
chemical process used for obtaining a metal from its oxide is
reduction. In this process, metal oxides are reduced by using
suitable reducing agents such as carbon or by highly reactive metals
to displace the metals from their oxides.
For
example, zinc oxide is reduced to metallic zinc by heating with
carbon.
Manganese
dioxide is reduced to manganese by treating
it with aluminium powder. In this case, aluminium displaces manganese
from its oxide.

Oxides of
more reactive metals are reduced by electrolysis.
Question 1:
Metallic oxides of zinc, magnesium and copper were heated with the
following metals.
Metal
|
Zinc
|
Magnesium
|
Copper
|
Zinc oxide
|
-
|
-
|
-
|
Magnesium oxide
|
-
|
-
|
-
|
Copper oxide
|
-
|
-
|
-
|
In which cases will you find displacement reactions taking place?
Answer:
Metal
|
Zinc
|
Magnesium
|
Copper
|
Zinc oxide
|
No reaction
|
Displacement
|
No reaction
|
Magnesium oxide
|
No reaction
|
No reaction
|
No reaction
|
Copper oxide
|
Displacement
|
Displacement
|
No reaction
|
Question 2:
Which
metals do not corrode easily?
Answer:
More
reactive a metal is, more likely it is to be corroded. Therefore,
less reactive metals are less likely to get
corroded. This is why gold plating provides high resistance to
corrosion.
Question 3:
What are alloys?
Answer:
Alloys
are homogeneous mixtures of two or more elements. The elements could
be two metals, or a metal and a non-metal. An alloy is formed by
first melting the metal and then dissolving the other elements in
it. For example, steel is an alloy of iron and carbon.