10 Chapter Electrochemistry Short Question With Answers PDF
10 Chapter Electrochemistry Short Question With Answers PDF
10 Chapter Electrochemistry Short Question With Answers PDF
CHAPTER 10
ELECTROCHEMISTRY
SHORT QUESTION WITH ANSWERS
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Q.1 Differentiate electrolytic and voltaic cell.
Ans.
An electrochemical cell in which electric current is used to drive a
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non–spontaneous redox reaction is called electrolytic cell. e.g.
electrolysis of molten NaCl.
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An electrochemical cell in which electricity is produced as a result of
spontaneous redox reaction is called Galvanic or voltaic cell e.g. Zn –
Cu cell.
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Q.2 Differentiate b/w ionization and electrolysis.
Ans.
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Q.4 Differentiate b/w oxidation and reduction.
Ans. Oxidation:
(i) Addition of oxygen
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(ii) Removal of electrons or
(iii) Removal of hydrogen is called as oxidation.
Reduction:
(i) Addition of hydrogen
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(ii) Addition of electrons or
(iii) Removal of oxygen is called as reduction.
Q.5 Define oxidation number. Write down the rules for assigning
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oxidation number.
Ans. Oxidation Number:
The apparent charge present on an atom in a molecule or ionic
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P+5O eq \a\co1(–3,4 ) eq \x( P = + 5 )
Q.6 K2Cr2O7 + HCl ( KCl + CrCl3 + Cl2 + H2O
Calculate the oxidation number of each element in above equation?
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Ans.
K eq \a\co1(+1(2),2 ) Cr eq \a\co1(+6(2),2 ) O eq \a\co1(–2(7),7
) + H+1Cl–1 ( fre
K+1Cl–1 + Cr+3 Cl eq \a\co1(–1(3),3 ) + Cl eq \a\co1(0,2) + H eq
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\a\co1(+1(2),2 ) O
Q.7 Calculate oxidation number of Cr in the following compounds.
(i) CrCl3 (ii) Cr2(SO4)3 (iii) K2CrO4
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2x – 6 = 0
2x = 6 eq \x( x = 3 )
(iii) K2CrO4 ( + 1 (2) + x + – 2 (4) = 0
= 2 + x – 8 = 0 eq \x( x = + 6 )
(iv) K2Cr2O7 ( + 1 (2) + 2x + – 2 (7) = 0
+ 2 + 2x – 14 = 0
2x – 12 = 0
2x = 12
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eq \x( x = + 6 )
(v) CrO3 ( x + (–2) 3 = 0
eq \x( x = + 6 )
(vi) Cr2O3 ( 2x + (–2) 3 = 0
2x – 6 = 0
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2x = + 6
eq \x(x = + 3 )
(vii) Cr2O eq \a\co1(–2,7 ) ( 2x + (–2) 7 = – 2
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2x – 14 = – 2
2x = + 12
eq \x( x = + 6 ) fre
Q.8 In a Galvanic cell chemical energy is converted to electrical
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energy. How?
Ans.
In galvanic cell chemical energy changes to electrical energy because
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to the anode and cathode of the cell respectively. Then the redox
cathode of the cell respectively. Then the redox reactions at respective
electrodes are reversed. Hence cell begins to recharge reaction at
cathode:
Pb eq \a\co1(+2 ,(aq)) + Ze– ( Pb eq \a\co1(0 ,(s)) (Reduction)
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PbSO4(s)
SO eq \a\co1(2–,4 ) (aq)
Reaction at Anode:
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+2H2O
Pb+2(aq) ( PbO2 + OH+ + 2e–
PbSO4(s)
SO eq \a\co1(2– ,4(aq))
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Overall Reaction:
2PbSO4(s) + 2H2O(l) ( Pb(s) + PbO2(s) + 4H+ + 2SO eq \a\co1(2–
,4(aq))
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(Ag2O) mixed with NaOH or KOH acts as cathode and zinc
functions as anode.
Q.14 Discuss reactions taking place in the Ni–Cd cell.
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Ans.
It is strong cell. The anode is made up of cadmium at which oxidation
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reaction takes place while cathode consists of NiO2. In this cell, an
alkaline electrolyte is used.
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Reactions:
At anode:
Cd(s) + 2OH eq \a\co1(– ,(aq)) ( Cd(OH)2(s) + 2e–
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The fuel cells are of great importance and used in space vehicles. In
these cells, electrodes are made up of porous compressed carbon,
which is impregnated with platinum. Which acts as catalyst. This fuel
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cell works at high temp in order to evaporate water, which is formed
in it. After condensation, this water can be used for drinking water for
astronauts. fre
Q.17 How prediction about feasibility of chemical reaction is made by
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electrochemical series?
Ans.
For a particular reaction, it is easy to predict whether it will take place
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Cu+2 ( Cu(s) E0 = + 0.34 v
E eq \a\co1(0 ,cell) = E eq \a\co1(0 ,Anode) + E eq \a\co1(0
,Cathode)
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= 0.76 + 0.34 = 1.10 v
Q.19 What are relative reactivity of metals? Explain by
electrochemical series?
Ans.
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Reactivity of a metal depends upon its ability to lose electrons to
change into M+ cation. It is clear from electrochemical series that
smaller the value of standard reduction potential, greater its tendency
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anode and that which has higher value of reduction potential acts as
cathode E0 eq \b( \f(Cu+2,Cu) ) = 0.34 has a lower value of
reduction potential than eq \f(E\a\co1(0 ,Ag+),Ag) = 0.80 v anode
and Ag as cathode.
Q.21 How we can predict whether it takes place or not?
Ans.
With the help of electrochemical series, it can be determined whether
a reaction will occur spontaneously or not. Consider the following
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reaction
Pb+2 + 2Ag0 ( 2Ag+ + Pb0
The reaction will occur only if E eq \a\co1(0 ,Cell) is positive
E eq \a\co1(0 ,Cell) = E eq \a\co1(0 ,Anode) + E eq \a\co1(0
,Cathode)
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E eq \a\co1(0 ,Cell) = E eq \a\co1(0 ,2Ag/Ag+) + E eq
\a\co1(0 ,Pb2+/Pb)
E eq \a\co1(0 ,Cell) = – 0.80 + (– 0.13)
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= – 0.93
E eq \a\co1(0 ,Cell) is negative so reaction will not take place
spontaneously. fre
Q.22 How can a non–metal displace another non–metal?
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Ans.
A non–metal of higher standard reduction potential can displace other
non–metal of lower standard reduction potential
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cell.
The combination of two or more cells is called battery.
Q.25 Outline the important applications of electrolysis?
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Ans.
(1) Electroplating
(2) Electro–refining
(3) Electro–manufacturing
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(4) Electrotyping
Q.26 What is salt bridge? Also give its function?
Ans:
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