NCERT Solutions for Class 10 Science 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.
Solution :
(i) Mercury
(ii) Sodium
(iii) Silver
(iv) Lead
2. Explain
the meaning of malleable and ductile.
Solution : 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.
3. Why is sodium kept immersed in kerosene oil?
Solution : 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.
4. Write equation for the reaction of
(i) Iron with
steam
(ii) Calcium
and potassium with water
Solution :
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 :
.png)
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.
Solution :
(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
6. Which gas is produced when dilute hydrochloric acid is added
to reactive metal?
Solution : 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.
Solution : As zinc is more reactive than iron, displacement reaction
will take place
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?
Solution :
(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-
9. Why do ionic
compounds have high melting points?
Solution : 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
Solution :
(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.
Solution : Gold and Platinum
12. What chemical
process is used for obtaining a metal from its oxide?
Solution : 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 :
In which case
will you find displacement reactions tking place?
Solution : Based on the activity series of metals, the displacement
reactions will take place as below:
14. Which metals do not
corrode easily?
Solution : Metals which are placed at the bottom of activity series
like silver, gold, platinum do not corrode easily.
15. What are alloys?
Solution : 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
Solution : (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
Solution : (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
Solution : (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
Solution : (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?
Solution :
(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.
21. What are amphoteric
oxides? Give two examples of amphoteric oxides.
Solution : 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.
Solution : 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?
Solution : Impure metal M is made the anode, thin strips of pure
metal M as cathode and a salt solution of metal M as electrolyte.
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.
Solution :
(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.
25. State two ways to
prevent the rusting of iron.
Solution : 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?
Solution : 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.
Solution :
(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.
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.
Solution : 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.
Solution : 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?
Solution : 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).
Solution : 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.
Either way the teacher or student will get the solution to the problem within 24 hours.