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NEET Chemistry MCQ
Redox Reactions And Electro Chemistry Mcq
Quiz 9
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Q.1
Consider the reaction Mn+(aq) + ne- → M(s) The standard reduction potential values of the elements M1, M2 and M3 are -0.34V, -3.05V and -1.66V respectively. the order of their reducing power will be [ NCRT 1990]
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a)M1 > M2 > M3
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b) M3 > M2 > M1
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c)M1 > M3 > M2
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d)M2 > M3 > M1
Explanation
More the negative reduction potential more reduction powerAnswer: (d)
Q.2
When Ag+/Ag=0.80 volts and Zn2+/ Zn=-0.76 volt, which of the following is correct? [ MP 1994]
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a) Ag+ can be reduced by H2
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b) Ag can oxidise H2 into H+ ion
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c)Zn2+ can be reduced by H2
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d)Ag can reduce Zn2+ ion
Explanation
Zn + 2Ag+ → 2Ag + Zn2+ Given oxidation values are for Oxidation potential but they should be positive for Zn and negative for Ag Thus Ag+ can be reduced bY H2 according to emf seriesAnswer: (a)
Q.3
When a solution of an electrolyte is heated, the conductance of the solution [ KCET 1991]
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a) increases because number of molecules of the electrolyte increases
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b) decreases because of the increased heat
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c)decreases because the dissociation of electrolyte is suppressed
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d)increases because the electrolyte is dissociated more
Explanation
Answer:(d)
Q.4
How long will it take for a current of 3 amperes to decompose 36g water? [ Eq. Wt of hydrogen is 1 and that of oxygen 8) [BHU 1992]
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a) 36 Hrs
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b) 18 Hrs
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c) 9 Hrs
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d) 4.5 Hrs
Explanation
2F charge is required to decompose 1 mole water=18gm Thus charge required to decompose 36 g=4F 4F=2×96500 C Now Q=It 4×96500=3 × t ∴ t=128666 sec=35.74=36HrsOr Equivalent weight of H2O=1+8=9 1 F charge decompose 9 gm of water To decompose 36g of water 4F charge is required Thus t=Q/I=(96500×4)/3=35.7 Hrs=36 hrs Answer: (a)
Q.5
In the electrolysis of NaCl: [ AFMC 1991]
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a)Cl- is oxidised at anode
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b) Cl- is reduced at anode
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c)Cl- is oxidised at cathode
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d)Cl- is neither reduced nor oxidised
Explanation
Answer: (a)
Q.6
A current of 2.0 A passed for 5 hours through a molten metal salt deposits 22.2 g of metal ( At Wt.=177]. The oxidation state of the metal in the metal salt is [ haryana CEET 1996]
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a) +1
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b) +2
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c)+3
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d)+4
Explanation
Charge Q=It Q=2 ×5×3600=36000 Now 96500 coulomb=1 Faraday 36000 C=36000/96500=360/965Farady Atomic weight of metal is 177 let x be the oxidation state then Equivalent mass=177/x Now Equivalent mass × Faraday charge=mass deposited Answer: (c)
Q.7
When a rod of metal A is dipped in an aqueous solution of metal B ( concentration of B2+=1M) at 25°C, the electrode potentials are A2+/A=-0.76 volts, B2+/B=+0.34 volts. [ KCET 1992]
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a)A will gradually dissolve
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b)B will deposit on A
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c)No reaction will occur
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d)Water will decompose into Hydrogen and Oxygen
Explanation
A + B2+ → B + A2+Above reaction is possible because A have negative reduction potential and B have positive reduction potential Answer:(a)
Q.8
An unknown metal M displaces nickel from nickel(II) sulphate solution but does not displace manganese from manganese sulphate solution. Which order represents the correct order of reducing power
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a) Mn > Ni > M
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b) Ni > Mn > M
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c) Mn > M > Ni
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d) M > Ni > Mn
Explanation
Mn is more reactive than M, M is more reactive than Ni thus reducing power is maximum for Mn and list for Ni Answer: (c)
Q.9
The correct order of chemical reactivity with water according to electrochemical series is ..[MP PMT 1991]
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a)K > Mg > Zn > Cu
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b) Mg > Zn > Cu > K
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c)K > Zn > Mg > Cu
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d)Cu > Zn > Mg > K
Explanation
Answer: (a)
Q.10
The standard EMF got the cell reactionZn + Cu2+ → Cu + Zn2+ is 1.1 Volt at 25°C The EMF for the cell reaction, when 0.1 M Cu2+ and 0.1M Zn2+ solution are used, at 25°C is [ Manipal PMT 2001]
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a) 1.10 V
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b) 0.10 V
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c)-1.10V
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d)-0.110 V
Explanation
Answer: (a)
Q.11
The cell reaction in Daniel cell is [ KCET 1992]
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a) Zn + Cu → Zn2+ + Cu2+
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b) Zn2+ + Cu → Zn + Cu2+
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c)Zn + Cu2+ → Zn2+ + Cu
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d)Zn2+ + Cu2+ → Zn + Cu
Explanation
Answer:(c)
Q.12
The voltage of a cell whose half cells are given below is Mg2+ + 2e- → Mg(s), -2.37 V Cu2+ + 2e- → Cu(s) , 0.34 V [EAMCET 1987]
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a) -2.03 V
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b) 1.36 V
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c) 2.71 V
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d) 2.03 V
Explanation
Both potentials are reduction potential E cell=reduction potential of ( cathode - Anode) E cell=0.34 - (-2.37 )=2.71 volts Answer: (c)
Q.13
What is the amount of Chlorine evolved when 2 amp of current is passed for 30 minutes in an aqueous solution of NaCl? [ AIIMS 1999]
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a)66 g
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b) 1.32 g
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c)33 g
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d)99 g
Explanation
Chlorine oxidation state is 1 thus 1F charge will evolve 1 mole of chlorine or half mole of chlorine gas∴ 2F=1 mole of Cl2=71 gAmount of charge passed Q=It Q=2 × 30 ×60=3600 Coulomb∴ 2×96500=71 g3600 coulomb=?3600×71) / (2×96500)=1.32 gAnswer: (b)
Q.14
The standard reduction potential for Fe2+/Fe and S2+ Sn electrodes are -0.44 and -0.14 volt respectively. For the cell reaction:Fe2+ + Sn → Fe + Sn2+, the standard emf is [ IIT 1990] < img id="hidden8" width="67px" height="15px"class="hidden8"alt="" src="images/c.png"/>
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a) +0.30 V
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b) -0.58 V
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c)+0.58 V
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d)-0.30 V
Explanation
Sn acts as anode (-0.14 volt) and Fe acts as cathode(-0.44 volt) E cell=reduction potential of ( cathode - Anode) E cell=-0.44 - (-0.14 )=-0.30Answer: (d)
Q.15
In a galvanic ell [ Pb CET 1994]
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a) Chemical energy is converted into electricity
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b) Chemical energy is converted into heat
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c)Electrical energy is converted into heat
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d)Electrical energy converted into chemical energy
Explanation
Answer:(a)
Q.16
If half cell reaction A +e- → A- has a large negative reduction potential, it follows that ..[ MLNR 1992]
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a) A is readily reduced
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b) A is readily oxidized
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c) A- is readily reduced
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d) A- is readily oxidized
Explanation
negative reduction potential of A is very large indicate very high oxidation potential of A- Thus A- is readily oxidised Answer: (d)
Q.17
Which of the following can be considered as a weal electrolyte [ harayana CEET 1991]
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a)NaCl
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b) HCl
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c)CH3COOH
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d)K2SO2
Explanation
Except option 'c' all are ionic compounds strong electrolyteAnswer: (c)
Q.18
The Nernst equation, Indicates that the equilibrium constant Kc will be equal to Q when
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a)E=Eo
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b) E=zero
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c)Eo=1
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d)RT/nF=1
Explanation
At equilibrium Q=Kc and E=0Answer: (b)
Q.19
Four moles of electrons were transferred from anode to cathode in an experiment on electrolysis of water. the total volume of the two gases ( dry and at STP) produced will be approximately ( in liters) [ AIIMS 1993]
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a) 22.4
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b) 44.8
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c)67.2
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d)89.4
Explanation
1F charge=1 mole electrons decomposes 9gm of water4mole decomposes 36 gm of water or two moles of water One mole of water gives 1 mole of H2 and half mole of O2=1.5 moles of gasesTwo moles of water will give 3 moles of gases=3 × 22.4=67.2 LAnswer: (c)
Q.20
Electrochemical equivalent of an element is [ CPMT 1991]
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a)
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b)
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c)
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d)
Explanation
Answer:(c)
Q.21
if the number of moles of electrons involved in a reaction is doubled by multiplying all of the species appearing in the overall reaction by 2 then the [ Bihar MDAT 1994]
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a) potential is halved
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b) potential is doubled
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c) potential is unchanged
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d) potential is squared
Explanation
Standard electrode potential for half-reaction is fixed Answer: (c)
Q.22
When current is passed through an electrolyte containing ions .. [ AFMC 1991]
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a)all ions move to oppositely charged plates
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b) ions do not move
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c)all ions moves to respective charged plates
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d)all the above facts are false
Explanation
Answer: (a)
Q.23
Which of the following reaction occurs at the cathode during the charging of lead storage battery? [ BHU 1993]
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a) Pb2+ + 2e- → Pb
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b) Pb2+ + SO42- → PbSO4
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c)Pb → Pb2+ +2e-
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d)PbSO4 + 2H2O → 2PbO2 +4H+ + SO2- +2e-
Explanation
Answer: (d)
Q.24
The conductivity of electricity required to liberate one gram equivalent of an element is called [ KCET 1992]
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a) increases on dilution slightly
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b) does not change on dilution
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c)decreases on dilution
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d)depends on density of electrolyte itself
Explanation
Answer:(a)
Q.25
The hydrogen electrode is dipped in a solution of pH=3 at 25°C. The potential of the cell would be ( the value of 2.303RT/F is 0.059 V) [ KCET 1993]
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a) 0.177 V
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b) 0.087 V
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c) -0.177 V
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d) 0.059 V
Explanation
H+ + e- → ½H2 Answer: (c)
Q.26
Which is not correct? the degree of dissociation of an electrolyte depends on [ MP PMT 1991]
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a)Nature of the electrolytes
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b) Catalytic action
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c)Dilution
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d)Temperature
Explanation
Answer: (b)
Q.27
Standard reduction potentials for Li+/Li; Zn2+/Zn; H+/H2 and Ag+/Ag are -3.05, -0.762, 0.00 and +0.80V respectively. Which of the following has highest reduction capacity? [ MP PMT 1992]
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a) Ag
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b) H2
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c)Zn
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d)Li
Explanation
Answer: (d)
Q.28
The electroplating with chromium is undertaken because [ MP PMT 1996]
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a) Electrolysis of chromium is easer
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b) Chromium can form alloy with other metals
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c)Chromium gives protective and decorative coating to the base metal
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d)Of the high reactivity of metallic chromium
Explanation
Answer:(c)
Q.29
A cell constructed by coupling a standard magnesium electrode has emf of 2.7 volts. if the standard reduction potential of copper electrode is +0.34 volts, that of magnesium electrode is [ KCET 1989]
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a) +3.04 volts
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b) -3.04 volts
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c) +2.36 volts
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d) -2.36 volts
Explanation
E cell=reduction potential of ( cathode - Anode) 2.7=0.34 - ( x) X=0.34 - 2.7=-2.36 Answer: (d)
Q.30
When CuSO4 is electrolyzed by platinum electrodes [ CBSE PMT 1993]
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a) Copper is liberated at cathode, sulphur at anode
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b) Copper is liberated at cathode, oxygen at anode
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c)Sulphur is liberated at cathode, oxygen at anode
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d)Oxygen is liberated at cathode, copper at anode
Explanation
Answer: (b)
0 h : 0 m : 1 s
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