CHAPTER-3 METALS AND NON-METALS
1. Give an example of metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with knife.
(iii) is best conductor of heat.
(iv) is poor conductor of heat.
Answer:
(i) Mercury
(ii) Sodium
(iii) Silver
(iv) Lead
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2. Explain the meaning of malleable and ductile.
Answer:
A substance that can be beaten into thin sheets is said to be
malleable. For example, iron, copper etc. A substance that can be drawn into
wires is called ductile. For example, gold, silver etc.
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3. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium reacts so vigorously with oxygen that it catches fire
when kept in the opens. Hence, to protect accidental fires, it is kept immersed
in kerosene oil.
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4. Write equation for the reaction of
(i) Iron with steam
(ii) Calcium and potassium with water
Answer:
(i) 3Fe(s) + 4H2O(g) FeO4(s) + 4H2(g)
Steam Iron (II, III)
oxide
-->(ii) Ca(s) + 2H2O(i) Ca(OH)2(aq) + H2(g)
Calcium Hydroxide
-->(iii) 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) + Heat
Potassium Hydroxide
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5. 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 Raction |
Displacement |
|
|
|
B |
Displacement |
|
No Raction |
|
|
C |
No Raction |
No Raction |
No Raction |
Displacement |
|
D |
No Raction |
No Raction |
No Raction |
No Raction |
Use the table given above to answer the f0llowing 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 order of decreasing
reactivity.
Answer:
(i) B is the most reactive metal
(ii)If B is added to a solution of copper (II) sulphate,
displacement reaction will take place. Blue colour of copper sulphate will fade
and red –brown copper will settle down.
(iii) The decreasing order of reactivity is:
B> A> C >D
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6. Which gas is produced when dilute hydrochloric acid is
added to reactive metal?
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.
Fe(s) + H2SO4(aq) → FeSO4(aq)
+ H2(g)
7. What would you observe when zinc is added to a solution of
iron(II) sulphate? Write the chemical reaction that takes place.
Answer:
As zinc is more reactive than iron, displacement reaction
will take place
-->FeSO4(aq) +
Zn(s) ZnSO4(aq) +
Fe(s)
Iron(II) Sulphate Zinc Sulphate
General Solution Colourless Solution
8. (i) Write the electro-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) Electron-dot structure for sodium, oxygen and magnesium
are
(ii)
(iii) Ions present in Na2O are Na+ and
O2-
Ions present in MgO are Mg2+ and O2-
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9. Why do ionic compounds have high melting points?
Answer:
There are strong forces of attraction between oppositely
charged ions in ionic compounds. Considerable amount of energy is required to
break strong inter-ionic force of attraction. Therefore, they have high melting
points.
10. Define the following terms :
(i) Minerals
(ii) Ores and
(iii) Gangue
Answer:
(i) Minerals- the element or compounds which occur naturally
in the earth crest are known as minerals.
(ii) Ores- Minerals from which metal can be extracted
profitably and easily are called ores.
(iii) Gangue- Impurities such as soil and sand which are
present in the minerals are called gangue.
11. Name two metals which are found in nature in the free
state.
Answer:
Gold and Platinum
12. What chemical process is used for obtaining a metal from
its oxide?
Answer:
A metal is obtained from its oxide by the process of
reduction.
13. Metallic oxide of zinc, magnesium and copper were heated
with following metals :
|
|
Metal |
Zinc |
Magnesium |
Copper |
|
1 |
Zinc Oxide |
|
|
|
|
2 |
Magnesium Oxide |
|
|
|
|
3 |
Copper Oxide |
|
|
|
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In which case will you find displacement reactions tking
place?
Answer:
Based on the activity series of metals, the displacement
reactions will take place as below:
|
|
Metal |
Zinc |
Magnesium |
Copper |
|
1 |
Zinc Oxide |
|
Displacement |
|
|
2 |
Magnesium Oxide |
|
|
|
|
3 |
Copper Oxide |
Displacement |
Displacement |
|
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14. Which metals do not corrode easily?
Answer:
Metals which are placed at the bottom of activity series like
silver, gold, platinum do not corrode easily.
15. What are alloys?
Answer:
An alloy is homogenous mixture of two or more metals or metal
and non-metal. It is obtained by first melting primary metal and then
dissolving the other element in it in definite proportion.
16. Which of the following pairs will give displacement
reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminum
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper
Answer:
(d) AgNO3 solution and copper
17. Which of the following method is suitable for preventing
an iron fry pan from rusting?
(a) Applying grease
(b) applying paint
(c) Applying coating of zinc
(d) All of the above
Answer:
(c) Applying coating of zinc
18. 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
Answer:
(a) Calcium
19. Food cans are coated with tin and not zinc because
(a) Zinc is costlier than tin
(b) Zinc has higher melting point
(c) Zinc is more reactive than tin
(d) Zinc is less reactive than tin
Answer:
(c) Zinc is more reactive than tin
20. You are given a hammer, a battery, a bulb, wires and
switch.
(a) How could you use them to distinguish between samples of
metals and non-metals?
(b) Asses the usefulness of these tests in distinguishing
between metals and non-metals?
Answer:
(a) Place the sample on an iron block. Strike with hammer. If
the sample takes the shape of a sheet, it is a metal. If it breaks into pieces,
it is a non-metal.
Set up the arrangement by using a bulb, a battery, wires and
switch. Insert the samples of metals and non-metals in the clips one by one and
turn the switch on. If the bulb glows, the sample is a metal, if not, then the
sample is non-metal.
(b)The above two methods can, in general, be used to
distinguish between metals and non-metals.
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21. What are amphoteric oxides? Give two examples of
amphoteric oxides.
Answer:
Metal oxides which show both acidic as well as basic behavior
are called amphoteric oxides. Such metal oxides react with both acids and
bases.
Example: Aluminum
oxide, zinc oxide
22. Name two metals which will displace hydrogen from dilute
acids, and two metals which will not.
Answer:
Magnesium and zinc metals displace hydrogen from dilute
acids. Copper and silver do not displace hydrogen from dilute acids.
23. In the electrolytic refining of a metal M, what would you
take as the anode, the cathode and the electrolyte?
Answer:
Impure metal M is made the anode, thin strips of pure metal M
as cathode and a salt solution of metal M as electrolyte.
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24. Pratyush took Sulpher powder on spatula and heated it. He
collected the gas evolved by inverting a test tube over it as shown in fig.
3.12 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.
Answer:
(a) Sulphur is a non-metal. Oxides of non-metals are acidic.
In this case sulphur dioxide is produced which is acidic.
(i) No action of the gas
(ii) wet litmus paper will turn red.
(b) S + O2 à SO2
SO2 +
H2O à H2SO3 (Sulphurous Acid)
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25. State two ways to prevent the rusting of iron.
Answer:
Rusting of iron can be prevented by
(i) By applying grease or paint.
(ii) By galvanizing
26. What types of oxides are formed when non-metals combine
with oxygen?
Answer:
Acidic oxides are formed when non-metals combine with oxygen.
27. Give reasons :
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminum is highly reactive metal, yet it is used to make
utensils for cooking.
(d) Carbonate and sulphides ores are usually converted into
oxides during the process of extraction.
Answer:
(a) These metals are un-reactive. They do not react with
oxygen and other gases present in air and with moisture. Thus, their shine is
maintained. That is why these metals are used to make jewellery.
(b) Reaction of sodium, potassium and lithium with oxygen is
so violent that they catch fire. To prevent accidental fire, they are stored
under kerosene oil.
(c) This is because aluminum is a good conductor of heat.
Aluminum forms a layer of aluminum oxide at high temperature which is prevent
the further corrosion.
(d) It is easier to reduce oxide than the carbonates and
sulphide to the metals.
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28. 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.
Answer:
Copper, on keeping in air reacts with atmospheric carbon
dioxide to form a green layer of copper carbonate. Copper carbonate reacts with
citric acid present in lemon or tartaric acid present in tamarind to form
soluble copper citrate or copper tartarate. The vessels are thus cleaned using
water.
29. Differentiate between metal and non-metal on the basis of
their chemical properties.
Answer:
Metals and non-metals can be differentiated on the basis of
following chemical properties.
30. A man went door to door posing as a goldsmith. He
promised to bring back the glitter of the old and dull 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?
Answer:
Aqua regia, which is a mixture of 3 parts concentrated HCl
and part of concentrated nitric acid dissolves gold. The man put the gold
bangles in this solution. The outer dirty layer of gold bangles dissolved in
aqua regia bring out the shining bangles.
As the outer layer of bangles dissolved in aqua regia, the weight was reduced
drastically.
31. Give reasons, why copper is used to make hot water tanks
and not steel (an alloy of iron).
Answer:
Electrical conductivity of a metal is decreased when it is
alloyed with another metal or non-metal. Thus, the electrical conductivity of
steel is much less than that of pure. That is why copper is used to make hot
water tanks and not steel.
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