Page: 40
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) Mercury (ii) Sodium
(iii) Silver (iv) Lead
2. Explain the meanings of malleable and ductile.
Answer:
Malleable
means a metal can be beaten into thin sheets.
Ductile means
a metal can be drawn into thin wires.
Page: 46
1. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium is highly reactive. So it is kept immersed in
kerosene oil to prevent reaction with atmospheric oxygen, moisture and CO2.
2. Write equations for the reactions of
(i) iron with steam.
(ii) calcium and potassium with water.
Answer:
(i) 3Fe
(s) + 4H2O (g) → Fe3O4
(s) + 4H2 (g)
(ii) Ca(s)
+ 2H2O(l) → Ca(OH)2(aq) + H2(g)
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
+ heat
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 |
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:
(i) B is the most reactive metal because 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 due to 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) 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.
Answer:
Hydrogen gas is produced.
Chemical reaction between iron and dilute H2SO4:
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.
Answer:
Zinc is more reactive than iron. Therefore, when zinc is
added to iron (II) sulphate solution, the greenish colour of the solution fades
gradually due to the formation of colourless zinc sulphate solution and iron
metal is deposited on zinc.
FeSO4(aq) + Zn(s) + → ZnSO4(aq) + Fe(s)
Page: 49
1. (i) Write the electron dot structures for sodium, oxygen
and magnesium.
(ii) Show the formation of Na2O and MgO by the
transfer of electrons.
(iii) What are the ions present in these compounds?
Answer:
|
(i) |
l Na |
ll l O l ll |
ll Mg |
|
(ii) |
Formation of Na2O
and MgO:  |
||
|
(iii) |
Ions present in
Na2O: Na+ and O2-. Ions present in
In MgO: Mg2+ and O2-. |
||
2. Why do ionic compounds have high melting points?
Answer:
In ionic compounds, there is a strong force of attraction
between the oppositely charged ions. So, much heat energy is needed to break
this force of attraction and melt the ionic compound. Therefore, ionic
compounds have high melting points.
Page: 53
1. Define the following terms: (i) Mineral, (ii) Ore and
(iii) Gangue.
Answer:
(i) Mineral: These
are the natural materials in which the metals or their compounds are found.
(ii) Ore: These are
the minerals from which the metals can be extracted conveniently and
profitably.
(iii) Gangue:
These are the unwanted impurities like sand, rocky material, earth particles,
lime stone, etc. in an ore.
2. Name two metals which are found in nature in the free
state.
Answer:
Gold and platinum
3. What chemical process is used for obtaining a metal from
its oxide?
Answer:
Reduction.
E.g., zinc oxide is reduced to metallic zinc by heating
with carbon.
ZnO(s) + C(s) → Zn(s) + CO(g)
4. Gold is Metal or Nonmetal?
Gold is a metal found in nature in the free state
Page: 55
1. Metallic oxides of zinc, magnesium and copper were heated
with the following metals:
|
Metal |
Zinc |
Magnesium |
Copper |
|
|
1 |
Zinc oxide |
|||
|
2 |
Magnesium oxide |
|||
|
3 |
Copper oxide |
In which cases will you find displacement reactions taking
place?
Answer:
A more reactive metal can displace a less reactive metal
from its oxide. Here, magnesium is most reactive, zinc is less reactive and
copper is least reactive.
|
Metal |
Zinc |
Magnesium |
Copper |
|
|
1 |
Zinc oxide |
– |
Displacement |
– |
|
2 |
Magnesium oxide |
– |
– |
– |
|
3 |
Copper oxide |
Displacement |
Displacement |
– |
2. Which metals do not corrode easily?
Answer:
Gold and Platinum.
3. What are alloys?
Answer:
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
E.g., bronze is an alloy of copper and tin.