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VERY SHORT ANSWER TYPE
QUESTIONS [1 MARK]
1. A green layer is gradually formed on a
copper plate left exposed to air for a week in a bathroom. What could this
green substance be?
Answer. It is
due to the formation of basic copper carbonate [CuC03.Cu(0H)2].
2. A non-metal X exists in two different forms
Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of
electricity. Identify X, Y and Z.
Answer. ‘X’ is
carbon, ‘Y’ is diamond as it is the hardest natural substance and ‘Z’ is
graphite as it is good conductor of electricity.
3. Metals generally occur in solid state. Name
and write symbol of a metal that exists in liquid state at room temperature.
Answer. Mercury(Hg)
exists in liquid state at room temperature.
4. Which of the following two metals will melt
at body temperature (37 °C) ? Gallium,
Magnesium, Caesium,
Aluminium
Answer. Gallium
and Caesium
5. From amongst the metals sodium, calcium,
aluminium, copper and magnesium, name the metal (a) which reacts with water
only on boiling, and (b) another which does not react even with steam.
Answer. (a)
Magnesium reacts with water only on boiling. (b) Copper does not react even
with steam.
6. Which one of the following metals does not
react with oxygen even at high temperatures ?
(a) Calcium (b)
Gold (c) Sodium
Answer. (b) Gold
does not react with oxygen even at high temperatures.
7. Name any one metal which reacts neither
with cold water nor with hot water, but reacts with heated steam to produce
hydrogen gas.
Answer. Iron; 3Fe(s) + 4H2O(g) → Fe3O4(s)
+ 4H2(g)
8. Why does calcium float in water?
Answer. It is
because hydrogen gas is formed which sticks to surface of calcium, therefore it
floats.
9. Name a non-metal which is lustrous and a
metal which is non-lustrous.
Answer. Iodine
is a non-metal which is lustrous, lead is a non-lustrous metal.
10. Which gas is liberated when a metal reacts
with an acid? How will you test the presence of this gas?
Answer. Hydrogen
gas is formed. Bring a burning matchstick near to it, H2 will burn explosively
with ‘pop’ sound.
11. Name the metal which reacts with a very
dilute HNO3 to evolve hydrogen gas. Answer. Magnesium
12. Name two metals which are found in nature
in the free state. Answer.(i)
Gold (ii) Silver
13. What is the valency of silicon with atomic
number 14? Answer. Its valency
is equal to 4.
14. What is the valency of phosphorus with
atomic number 15? Answer.
Phosphorus has valency 3.
15. What is the valency of an element with
atomic number 35?
Answer. Its
valency is 1.
16. Arrange the following metals in the
decreasing order of reactivity: Na, K, Cu, Ag. Answer. K > Na > Cu
> Ag
17. An element forms an oxide, A2O3 which is
acidic in nature. Identify A as a metal or nonmetal.
Answer. ‘A’ is
non-metal as non-metallic oxides are acidic in nature.
18. A green layer is gradually formed on a
copper plate left exposed to air for a week in a bathroom. What could this
green substance be ?
Answer. It is
due to the formation of basic copper carbonate [CuCO3.Cu(OH)2].
SHORT ANSWER TYPE
QUESTIONS[I] [2 MARKS]
19. Write one example of each of
(i) a metal which is so soft that, it can be
cut with knife and a non-metal which is the hardest sustance.
(ii) a metal and a non-metal which exist as
liquid at room temperature.
Answer.
(i) Sodium, carbon (diamond).
(ii)Mercury is liquid metal, bromine is liquid non-metal.
20. Mention the names of the metals for the
following:
(i) Two metals which are alloyed with iron to
make stainless steel.
(ii) Two metals which are used to make
jewellary.
Answer.
(i) Nickel and chromium. (ii) Gold and platinum.
21. Give reason for the following:
(a) School bells are made up of metals.
(b) Electric wires are made up of copper.
Answer.
(a) It
is because metals are sonorous, i.e. they produce sound when struk with a hard
substance.
(b) It-is
because copper is good conductor of electricity.
22. Name the following:
(a) A metal, which is preserved in kerosene.
(b) A lustrous coloured non-metal.
(c) A metal, which can melt while kept on palm.
(d) A metal, which is a poor conductor of heat.
Answer.
(a) Sodium
is preserved in kerosene.
(b) Iodine
is lustrous coloured non-metal. (c) Gallium. ‘ (d) Lead.
23. Explain why calcium metal after reacting
with water starts floating on its * surface. Write the chemical equation for
the reaction. Name one more metal that
starts floating after some time when immersed in water.
Answer. Calcium
starts floating because the bubbles of hydrogen gas formed stick to the surface
of metal.
Magnesium reacts with hot water and starts floating due to
the bubbles of hydrogen gas sticking to its surface.
24. Give reason for the following:
(a) Aluminium oxide is considered as an
amphoteric oxide.
(b) Ionic compounds conduct electricity in
molten state.
Answer.
(a) It is because it reacts with acids as well as
bases to produce salts and water.’Al’ is less electropositive metal. So, it
forms amphoteric oxide which can react with acid as well as base. (b) Ionic
compounds can conduct electricity in molten state because ions ’ become free to
move in molten state.
25. Write two differences between calcination
and roasting. Answer.
26. The way, metals like sodium, magnesium and
iron react with air and water is an indication of their relative positions in
the ‘reactivity series’. Is this statement true ? Justify your answer with
examples.
Answer.Yes,
sodium reacts explosively even with cold water, it is most reactive. Magnesium
reacts with hot water, it is less reactive than Na. Iron reacts only with steam
which shows it is least reactive among the three.
27. X + YSO4——-> XSO4+
Y
Y + XSO4
——–> No reaction
Out of the two
elements, ‘X’ and ‘Y’, which is more reactive and why?
Answer. ‘X’ is
more reactive than ‘Y’ because it displaces ‘Y’ from its salt solution.
28. What is an alloy? State the constituents of
solder. Which property of solder makes it suitable for welding electrical
wires?
Answer. Alloy is a homogeneous
mixture of two or more metals. One of them can be a non-metal also. Solder
consists of lead and tin. It has low melting point which makes it suitable for
welding electrical wires.
29. Using the electronic configurations,
explain how magnesium atom combines with
oxygen atom to form magnesium oxide by transfer of electrons. Answer.
30. When a metal X is treated with cold water,
it gives a base Y with molecular formula XOH (Molecular mass = 40) and
liberates a gas Z which easily catches fire. Identify X, Y and Z. Answer.
31. (a) Give two methods to prevent the rusting
of iron.
(b) Name the ores
of the following metals:
(i) mercury, and
(ii) zinc
Answer.
(a)(i) Painting (ii) Galvanisation
(b)(i) Cinnabar
(ii) Zinc Blende
32. Write chemical equations that shows
aluminium oxide reacts with acid as well as base. Answer.
33. Elements magnesium and oxygen respectively
belong to group 2 and group 16 of the Modern Periodic Table. If the atomic
numbers of magnesium and oxygen are 12 and 8 respectively, draw their
electronic configurations and show the process of formation of their compound
by transfer of electrons.
Answer.
Mg(12)=2,8,2
SHORT ANSWER TYPE QUESTIONS[II]
[3 MARKS]
34. State three reasons for the following facts
(i) Sulphur is a
non-metal
(ii)Magnesium is a
metal
One of the
reasons must be supported with a chemical equation. Answer.
|
Sulphur is a
non-metal |
Magnesium is a metal
|
|
(i) Poor conductor of
heat and electricity |
(i)
Good conductor of heat and electricity |
|
(ii) Neither malleable
nor ductile |
(ii)
Malleable nor ductile |
|
(iii) S + O2 →SO2
SO2 + H2O → H2SO3 (Sulphurous
acid) Sulphur dioxide is acidic
oxide. |
(iii) 2Mg + O2 →2MgO2
MgO + H2O → Mg(OH)2
(Magnesium
hydroxide) Magnesium oxide is
basic in nature. |
35. What is cinnabar? How is metal extracted
from cinnabar? Explain briefly.
Answer. Cinnabar
is HgS.
Mercury is obtained by roasting cinnabar. HgO formed is
thermally unstable and gives mercury.
Mercury can be purified by distillation.
36. (a) Write the electron dot structures for
potassium and chlorine.
(b) Show the formation of KCl by the transfer
of electrons. (c) Name the ions
present in the compound, KCl.
Answer.
37. (a)State the electron-dot structure for
calcium and sulphur.
(b) Show the formation of CaS by the transfer
of electrons.
(c) Name the ions present in this compound CaS.
Atomic number of Ca = 20, O = 16. Answer.
38. You are given samples of three metals.
Sodium, magnesium and copper. Suggest any two activities to arrange them in
order of decreasing activity.
Answer. Activity 1: Sodium reacts with cold
water vigorously to form sodium hydroxide and hydrogen gas
Magnesium does not react with cold water but with hot water
to form magnesium ! hydroxide and hydrogen gas.
Hence sodium is more reactive than magnesium.
39. You are provided with magnesium ribbon and
sulpher powder. Explain with the help of an activity that metal oxides are
basic and non-metal oxide are acidic in nature.
Answer.
Aim: To test the
nature of oxides formed by metals and non-metals. Materials Required: Sulphur
powder, Mg ribbon, water, blue litmus paper, red litmus paper. Procedure:
1.Take magnesium ribbon with a pair of tongs and burn
it in flame in the presence of air.
2.Collect the product formed and dissolve it in warm water.
3.Add red litmus paper into it.
4.Observe the change in colour and decide the nature of the
oxide formed.
5.Burn sulphur in a deflagrating spoon in the presence of
air and dissolve the oxide formed in water.
6.Dip blue litmus paper into the solution and observe the
changein the colour and decide the nature of the oxide formed.
Observation: The
oxide formed by metal turns red litmus blue whereas oxide of non-metal turns
blue litmus red.
Chemical Reaction:
Conclusion: Most
of the metallic oxides are basic in nature whereas most of the non-metallic
oxides are acidic in nature.
40. Suggest a method of reduction for the
following metals during their metallurgical processes:
(i) metal ‘A’ which is one of the last, second
or third position in the reactivity.
(ii) metal ‘B’ which gives vigorous reaction
even with water and air.
(iii) metal ‘C’ which is kept in the middle df
activity series.
Answer.
(i) ‘A’
can be obtained by chemical reduction using carbon or carbon monoxide as
reducing agent.
(ii) ‘B’
can be obtained by electrolytic reduction.
(iii) ‘C’ can be
reduced by reducing agent like ‘Al’.
41. (a) Explain the formation of ionic compound
CaO with electron dot structure. Atomic number of calcium and oxygen are 20 and
8 respectively.
(b) Name the
constituent metals of bronze. Answer.
42. A metal ‘X’ acquires a green colour coating
on its surface on exposure to air. (i)
Identify the metal ‘X’ and name the process responsible for this change.
(ii)Name and write
chemical formula of the green coating formed on the metal.
(iii) List two
important methods to prevent the process.
Answer.
(i) Metal
is copper. The process is corrosion.
(ii)Basic copper carbonate [CuCO3.Cu(0H)2].
(iii)
• It
should be coated with tin
• It
should be mixed with other metals to form alloys
43. Write balanced equations for the reaction
of:
(i) aluminium when heated in air. Write the
name of the product.
(ii) iron with steam. Name the product obtained.
(iii) calcium with water. Why does calcium start
floating in water? Answer.
44. Write balanced chemical equations for the
following reactions: (a) Dilute
sulphuric acid reacts with aluminium powder.
(b) Dilute hydrochloric acid reacts with sodium
carbonate.
(c) Carbon dioxide is passed through lime
water. Answer.
45. What is meant by ‘rusting’? With labelled
diagrams, describe an activity to find out the conditions under which iron
rusts.
Answer.
The process in which iron reacts with oxygen in the presence of moisture to
form reddish brown coating of hydrated ferric oxide [Iron (III) oxide].Fe2O3
xH20 Activity:
(i) Take
three boiling tubes A, B and C.
(ii) Pour
some water in test tube A Put iron nails in it and cork it.
(iii) Pour
boiled distilled water in another test tube B and put iron nails in it. Add 1
ml of ojl over it such that oil flo’ats over it and prevents the air from
entering.
(iv) Take
some iron nails in test tube C and put some anhydrous calcium chloride in it
and cork it. (v) Leave all the three test tubes for one day and then observe.
Observation:
Iron nails get rusted in test tube A because both air and water are present in
it. Iron nails do not get rusted in B because there is water but no air. In C,
rusting will not take place because there is neither air nor water. Conclusion:
Iron gets rusted in the presence of air and water.
46. (a) Show the formation of Na2O
by the transfer of electrons between the combining atoms. (b) Why are ionic compounds usually hard?
(c) How is it that
ionic compounds in the solid state do not conduct electricity but they do so
when in molten state? Answer.
(b) It
is due to strong force of attraction between oppositely charged ions.
(c) In
solid state, ions are not free to move whereas in molten state ions are free to
move, therefore, they conduct electricity in molten state.
47. (a) Show on a diagram the transfer of
electrons between the atoms in the formation of MgO. Write symbols of cation
and anion present in MgO.
(b) Name the solvent in which ionic compounds
are generally soluble.
(c) Why are aqueous solutions of ionic
compounds able to conduct electricity?
Answer.
(b) Ionic
compounds are soluble in water.
(c) It
is because aqueous solutions consist of ions which can move freely in them and
carry current.
48. What are amphoteric oxides? Choose the
amphoteric oxides from amongst the following oxides:
Na2O,
ZnO, Al2O3, CO2, H2O
Answer.Those
oxides which reacts with acids as well as bases to produce salts and water are
called amphoteric oxides, e.g. Na2O, ZnO, are amphoteric oxides
among given oxides.
49. Define the terms:
(i) mineral (ii) ore, and (iii) gangue.
Answer.
(i) Mineral: It is a naturally occurring substance from
which metal may or may not be extracted profitably or economically, e.g. A1
cannot be extracted profitably from mica.
(ii)Ore: It is a rocky material which contains sufficient
quantity of mineral so that metal can be extracted profitably, e.g. zinc blende
is an ore of zinc from which zinc can be extracted profitably. (iii) Gangue: It
is a rocky material which is present along with the mineral in the ore, e.g.
FeO is gangue in extraction of copper.
50. An ore on heating in air produces sulphur
dioxide. Which process would you suggest for its concentration? Describe
briefly any two steps involved in the conversion of this concentrated ore into
related metal.
Answer. It is
concentrated by froth-floatation process.
(i) Roasting:
The concentrated sulphide ore is heated strongly in the presence of oxygen to
convert it into its oxide.
(ii)Reduction : This oxide of metal is reduced with
suitable reducing agent to get free metal.
51. Give reasons for the following
observations:
(i) Ionic compounds in general have high
melting and boiling points. (ii)
Highly reactive metals cannot be obtained from their oxides by heating them with carbon.
(iii) Copper vessels
get a green coat when left exposed to air in the rainy season. Answer. (i) Ionic compounds have high
melting and boiling points due to strong force of attraction between oppositely
charged ions.
(ii) It
is because these metals themselves are strong reducing agents. Therefore,
cannot be reduced by reducing agent like carbon.
(iii) Copper
vessels react with CO2, O2 and moisture to form
green-coloured basic copper carbonate
[CuCO3.Cu(OH)2].
52. State reasons for the following
observations:
(i) The shining surface of some metals becomes
dull when exposed to air for a long time.
(ii) Zinc fails to evolve hydrogen gas on
reacting with dilute nitric acid.
(iii) Metal sulphides occur mainly in rocks but
metal halides occur mostly in sea and lake waters.
Answer.
(i) It
is because metal reacts with substances present in atmosphere to form surface
compounds which make it dull.
(ii) It
is because dil. HNO3 is an oxidising agent therefore zinc gives NO
and not H2 with dil. HNO3.
(iii) It is
because sea water contains sodium chloride due to which metal halides are
formed, whereas sulphur is found below rocks. Therefore, metal – sulphides are
formed in rocks.
53. State reasons for the following:
(i) Electric wires are covered with rubber like
material.
(ii)From dilute
hydrochloric acid, zinc can liberate hydrogen gas but copper cannot.
(iii) Sulphide ore
of a metal is first converted to its oxide to extract the metal from it.
Answer.
(i) It
is because rubber is an insulator and does not allow current to flow through
it.
(ii) Zinc
is more reactive than hydrogen. Therefore, it can displace hydrogen from dilute
HCl whereas copper cannot, because it is less reactive than hydrogen. ,
(iii) It is
because it is easier to reduce oxide ore as compared to sulphide ore.
Long Answer Type Question [5
Marks]
54. (a) Write electron dot diagram for chlorine
(At No. 17) and calcium (At No. 20). Show
the formation of calcium chloride by transfer of electrons.
(b) Identify the nature of above compound’and
explain three physical properties of such compound. Answer.
(b) It is ionic compound.
Physical properties
1.It is hard and solid.
2.It has high melting and boiling point.
3.It soluble in water.
55. (a) An ore on treatment with dilute
hydrochloric acid produces brisk effervesces. What type of ore is this? What
steps will be required to obtain metal from the enriched ore. ,
(b) Copper coin is kept immersed in silver
nitrate solution for some time. What change will take place in coin and colour
of the solution ? Write balanced chemical equation of the reaction involved.
Answer.
(a) Carbonate ore:
(i) Calcination: Carbonate ore is heated in
limited supply of air and oxide is obtained, e.g.
(b) Copper, being more reactive than silver will
displace silver from silver nitrate solution and there will be deposition of
silver on copper coin. The colour of solution will turn to blue.
56. (a) Define activity series of metals.
Arrange the metals gold, copper, iron and magnesium in order of their increase
in reactivity.
(b) What will you observe when:
(i) Some zinc pieces are put in copper sulphate
solution.
(ii) Some silver pieces are put into green
coloured ferrous sulphate solution.
Answer.
(a) The
series of metals in which metals are arranged in decreasing order of their
reactivity.
Au < Cu < Fe < Mg is increasing order of
reactivity.
(b) (i)
The blue solution will become colourless and reddish brown copper metal will be
deposited.
Reaction will not take place because Ag’ is less reactive
than iron.
57. (a) Write the chemical name of the coating
that forms on silver and copper articles when these are left exposed to moist
air.
(b) Explain what is galvanisation. What purpose
is served by it?
(c) Define an alloy. How are alloys prepared?
How do the properties of iron change when:
(i) small quantity of carbon,
(ii) nickel and chromium are mixed with it.
Answer.
(a) Ag2S
(silver sulphide) is formed on silver, basic copper carbonate CuCO3.
CU(OH)2 is formed on copper.
(b) The
process of coating zinc over iron is called galvanisation. It is used to
prevent rusting of iron.
(c) Alloy
is a homogeneous mixture of two or more metals. One of them can be non-metal.
Alloys are prepared by melting two or more metals together.
(?) Iron does not rust on adding small,quantity of carbon.
(ii) When we form alloy of iron with nickel and
chromium, we get stainless steel which is malleable and does not get rusted.
58. (a) Differentiate between roasting and
calcination. Explain the two with the help of suitable chemical equations. How
is zinc extracted from its ore?
(b) Name two metals that can be used to reduce
metal oxides to metals.
Answer.
(a) Roasting:
It is a process in which sulphide ore is heated in the presence of oxygen to
convert into oxide.
Cali ination: It is a process in which carbonate ore is
heated in the absence of air to form oxide.
By reduction process, Zn can be extracted from its ore.
(b) Aluminium,
Magnesium.
59. (a) In the formation of compound between
two atoms A and B, A loses two electrons and B gains one electron.
(i) What is the nature of bond between A and B?
(ii) Suggest the formula of the compound formed
between A and B. (b) On similar lines explain the formation of MgCl2
molecule.
(c) Common salt conducts electricity only in
the molten state. Why?
(d) Why is melting point of NaCl high? Answer.
60. (a) Carbon cannot be used as reducing agent
to obtain Mg from MgO. Why?
(b) How is sodium obtained from molten sodium
chloride? Give equation of the reactions.
(c) How is copper obtained from its sulphide
ore? Give equations of the reactions.
Answer.
(a) It is because ‘Mg’ is stronger reducing agent
than carbon. (b) Sodium is obtained from molten NaCl by electrolysis.
Blister Copper is purified by electrolytic refining.
61. How is the method of extraction of metals
high up in the reactivity series different from that for metals in the middle ?
Why the same process cannot be applied for them? Explain giving equations, the
extraction of sodium.
Answer. Metals
high up in the series are obtained by electrolytic reduction because these
metals are strong reducing agents and therefore, cannot be obtained by chemical
reduction.
Metals in middle of series are less reactive and can be
obtained by chemical reduction. The same process can not be used for both of
them as highly reactive metals can not be obtained by chemical reduction.
Extraction of sodium is done by electrolysis of molten
sodium chloride.
62. Write the names and symbols of two most
reactive metals. Explain by drawing electronic structure how any one of the two
metals react with a halogen. State any four physical properties of the compound
formed.
Answer. K(Potassium)
and Na(Sodium) are the two most reactive metals. K’ and Na‘ are electronic
structures as they have one valence electron.
where ‘F’ is a halogen.
Four physical properties of the compounds formed by
these elements and halogens are:
(i) They have high melting point.
(ii)They are soluble in water.
(iii) They conduct electricity in molten state not in
solid state. (iv) They are solid and somewhat hard.
63. A metal ‘M’ which is one of the best
conductor of heat and electricity used in making electric wires is found in
nature as sulphide ore M2S?
(i) Name the metal ‘M’
(ii) Which process will be suitable for
extraction of this metal M from its ore M2S? Write the balanced chemical
reactions involved in the process of ‘ extraction.
(iii)
With
the help of a labelled diagram, explain the process of electrolytic refining of
the metal.
Answer.
(i) Copper
(ii) It
is concentrated by froth-floatation process.
Impure copper is purified by electrolytic refining.
(iii)
1)The electrolytic tank containing acidified copper
sulphate solution as electrolyte.
2) A
thick block of impure copper metal is made anode.
3) A
thin strip of pure copper metal is made cathode.
On passing electric current,impure copper from the anode
dissolves and goes into copper sulphate solution and pure copper from copper
sulphate deposits on cathode.Thus pure copper metal is produced on the
cathode.The soluble impurities go into the solution whereas insoluble
impurities collect below the anode as anode mud.
At cathode, Cu2+ + 2e– —> Cu
At anode, Cu – 2e– —–> Cu2+
64. Give reasons for the following:
(i) Silver and copper lose their shine when
they are exposed to air. Name the substance formed on their surface in each
case.
(ii) Tarnished copper vessels are cleaned with
tamarind juice.
(iii)
Aluminium
is more reactive than iron yet there is less corrosion of aluminium as compared
to iron when both are exposed to air.
Answer.
(i) These
metals get corroded. Silver forms black Ag2S (silver sulphide) and
copper form greenish layer of basic copper carbonate CuCO3. Cu(OH)2
.
(ii) Tamarind
contains acid which reacts with basic copper carbonate and product gets
dissolved and removed from copper vessel.
(in) Aluminium forms oxide layer on its surface which does
not further react with air.
65. (a) Write the electron dot structures of
sodium, oxygen and magnesium.
(b) Show the formation of Na2O and
MgO by transfer of electrons. Name the ions present in these compound.
(c) List three properties of ionic compounds.
Answer.
(i) They
are solids having high melting point.
(ii) They
are soluble in water.
(iii) They
conduct electricity in molten state as well as in aqueous solution.
66. What are alloys? How are they made? Name
the constituents and uses of brass, bronze and solder.
Answer. Alloys are
homogeneous mixtures of two or more metals. One of them can be a nonmetal also.
They are made by melting a metal which is in large amount first and then adding
the other metal. ,
Brass contains copper and zinc. It is used for making
decorative articles. Bronze contains copper and tin. It is used for making
statues and medals. Solder contains lead and tin. It is used for soldering
purposes.
67. A metal (E) is stored under kerosene. When
a small piece of it is left open in the air, it catches fire. When the product
formed is dissolved in water, it turns red litmus to blue.
(i) Name the metal
(E).
(ii)Write the
chemical equation for the reaction when it is exposed to air and when the
product is dissolved in water.
(iii) Explain the
process by which the metal is obtained from its molten chloride.
Answer.
(i) ‘E’ is sodium which catches fire in presence of
moisture.
(iii) Electrolytic reduction: Electric current is passed
through molten NaCl. Sodium is formed at cathode and chlorine gas is liberated
at anode.
68. (a) Name the main ore of mercury. How is
mercury obtained from its ore? Give balanced chemical equation.
(b) What is thermite reaction? How is it used
to join the railway tracks or cracked machine parts?
(c) Name the method used to extract metals of
high reactivity.
Answer.
(a) Cinnabar
Mercury is obtained from its ore by roasting.
(b) When
aluminium is heated with Fe2O3 to get molten iron, it is
called thermite reaction.
Molten iron is used to weld broken railway tracks.
(c) Electrolytic
reduction
69. (a) How can the metals at the top of the
reactivity series be extracted from their ores?
Explain with an
example.
(b) Name any one alloy made from (i) a metal and a non-metal, and (ii) two metals.
Answer.
(a) These
metals are extracted by electrolytic reduction, e.g. aluminium is obtained from
bauxite by electrolytic reduction.
(b) (i)
Steel is made up of iron and carbon. (ii) Brass is made up of copper and zinc.
70. With the help of a suitable example,
explain how ionic compounds are formed. State any three general properties of
ionic compounds.
Answer.Ionic
compounds are formed by transfer of electrons from metal to non-metals, e.g.
General Properties:
(i) They
are the solids having high melting point.
(ii) They
are soluble in water.
(iii) They
conduct electricity in molten state as well as in aqueous solution.
71. (a) Explain with an example how the metal
(X) which is low in reactivity series and metal (Y) which is high in the
reactivity series are obtained from their compounds by reduction process.
(b) Write the electronic configurations of
sodium and chlorine. Show the formation of sodium chloride from sodium and
chlorine by the transfer of electrons.
(c) List any two observations when a highly
reactive metal is dropped in water.
Answer.
(a) ‘X’ is obtained by chemical reduction. ‘Y’ is
obtained by electrolytic reduction.
(c) (i) Metal will catch fire.
(ii) Alkali solution is formed which turns red litmus blue.
72. (a) The reaction of metal (X) with ferric
oxide is highly exothermic. Metal
(X) is
obtained from its oxides by electrolytic reduction. Identify (X) and write its
reaction with ferric oxide.
(b) Give reason to justify that aluminium oxide
is an amphoteric oxide. Also, give another example of amphoteric oxide.
(c) Mention constituent metals present in
bronze.
Answer. (a) ‘X’
is ‘Al’
(b) AI2O3
reacts with acid as well as base therefore it is amphoteric oxide.
Zinc oxide is also an amphoteric oxide.
(c) Bronze
contains’ copper and tin.
73. No reaction takes place when granules of a
solid ‘A’ are mixed with a powder of solid ‘B\ However when the mixture is
heated, a reaction starts with evolution of much heat. Product ‘C’ of the
reaction settles down as a liquid metal and solid product ‘D’ keeps floating
over the liquid ‘C\ This reaction is sometimes used for making metals for ready
use in odd places. (i) Based on this
information, make assumptions about ‘A’ and ‘B’ and corresponding deductions
about ‘C’ and ‘D’ and write a balanced chemical equation for the reaction.
Include in the chemical equation about physical states of the reactants and
products, need of heating for starting the reaction and the reaction being
exothermic.
(ii) Name two types
of chemical reactions to which this reaction can belong.
Answer.
(i) ‘A’ is aluminum, ‘B’ is ferric oxide [Iron(III) oxide],
(ii)This reaction is displacement reaction because AT is
displacing ‘Fe’. It is also a redox reaction because AT is reducing agent and
Fe2O3is oxidising agent.
74. (a) What is meant by corrosion? Name any
two methods used for the prevention of
corrosion.
(b) Suppose you have to extract metal M from
its enriched sulphide ore. If M is in the middle of the reactivity series,
write various steps used in extracting this metal. Answer. (a) Corrosion is a process in which metal reacts with
substances present in the environment to form surface compounds.
Prevention:
(i) Galvanisation
is a process to prevent corrosion of iron.
(ii)Electroplating is also used to prevent corrosion.
(b)(i) Concentration of ores: Sulphide ore will be
concentrated by froth- floatation process. Sulphide ore will be collected in
froth whereas gangue will be left behind.
(ii) Roasslng:
Sulphide ore is heated strongly in the presence of O2 to form metal
oxide and sulphur dioxide.
2MS + 3O2 ————- ► 2MO + 2SO2
(iii) Reduction:
MO reacts with carbon (acts as reducing agent) to form metal and CO.
MO + C —-> M + CO
(iv) Electrolytic
refining: Impure metal ‘M’ is purified by electrolytic refining. Impure metal
is taken as anode, pure metal is taken as cathode, soluble salt of metal is
taken as electrolyte. Impure metal forms metal ions which gain electrons and
form pure metal at cathode.
75. (a) Distinguish between ionic and covalent
compounds under the following properties:
(i) Strength of forces between constituent
elements.
(ii) Solubility of compounds in water.
(iii) Electrical conduction in substances.
(b) Explain how the following metals are
obtained from their compounds by the reduction process:
(i) Metal M which is in the middle of the
reactivity series.
(ii) Metal N which is high up in the reactivity
series.
Give one
example of each type. Answer.
|
Ionic Compounds |
Covalent Compounds |
|
(i) Strength – They have strong
forces of attraction |
They
have weak forces of attraction. |
|
(ii) Solubility – They are soluble in
water |
They
are insoluble in water |
|
(iii)
Conduction – They conduct electricity in aqueous solution. |
They
do not conduct electricity in aqueous solution. |
(b) (i) Metal M which is in the middle of the reactivity
series is reduced by aluminium, e.g.
3MnO2(s) + 4Al(s) ——–> 2Al2O3(s) +
3Mn(l)
(ii) Metal N will be obtained by electrolytic
reduction, e.g. A1 is obtained by electrolytic reduction.
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