Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

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Q.1. Given that the standard potentials (E°) and Cu2+/Cu and Cu+/Cu are 0.34 V and 0.522 V respectively, the E° of Cu2+/Cuis    (2020)
(1) 0.182 V
(2) +0.158 V
(3) −0.182 V
(4) −0.158 V

Ans. (2) 

Given,
Cu2+ + 2e- → Cu; E° 0.34 V       (1)
Cu+ + e→ Cu; E° = 0.522 V      (2)
For Cu2+ + e- → Cu+ ; E°Cu2+/Cu+ x V
On reversing Eq. (2), we get
Cu → Cu+ + e- ; E° = - 0.522 V      (3)
From Eq. (1) and Eq. (3), we get
ΔG°= ΔG°1 + ΔG°2
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
⇒ E°3 = 2 x 0.34 + (- 0.522)
⇒ E°3 = 0.68 - 0.522 = 0.158 V

Q.2. The equation that is incorrect is:    (2020)
(1)Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(2)Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(3)Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(4)Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Ans. 
(4) 

According to Kohlrausch law of independent migration of ions, the incorrect equation is:
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
From L.H.S
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
From R.H.S
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Hence, L.H.S is not equal to R.H.S.

Q.3. What would be the electrode potential for the given half-cell reaction at pH = 5?
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(R = 8.314 J and mol−1 K−1; T = 298 K; oxygen under standard atm pressure of 1 bar)    (2020)
Ans. (1.525)

 For the half-cell reaction,
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev    (1)
Substituting the values in Eq. (1), we get
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
⇒ Ecell = + 1.23 + 0.059 x 5    [Given: pH = 5]
⇒ Ecell = 1.525 V

Q.4. For an electrochemical cell
Previous year Questions (2016-20) - Electrochemistry Notes | EduRevthe ratioPrevious year Questions (2016-20) - Electrochemistry Notes | EduRevwhen this cell attains equilibrium is _______.
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev    (2020)

Ans. (2.15)

For the given electrochemical cell
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
= 0.13 - (-0.14) = 0.01 V
From the Nernst equation for given electrochemical cell
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev    (1)
Substituting the given values in Eq. (1), we get
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev [At Equilibrium, Ecell = 0]
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev    (2)
Taking antilog of Eq. (2), we get
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.5. 108 g of silver (molar mass 108 g mol-1) is deposited at cathode from AgNO3(aq) solution by a certain quantity of electricity. The volume (in L) of oxygen gas produced at 273 K and 1 bar pressure from water by the same quantity of electricity is ________ .    (2020)
Ans. (5.67) 

The moles of AgNO3 deposited at cathode
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
At anode: Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
At cathode:Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Thus, 1 F required to deposit 1 mol of Ag and 2 F required to produce 0.5 mol of oxygen gas.
⇒ 1 F will produce 0.25 mol of oxygen gas.
Thus, the volume of oxygen gas produced at 273 K and 1 bar pressure can be calculated using ideal gas equation.
⇒ pV = nRT
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.6. Amongst the following, the form of water with the lowest ionic conductance at 298 K is    (2020)
(1) distilled water
(2) saline water used for intravenous injection
(3) water from a well
(4) sea water

Ans. (1) 

Due to the absence of the mineral in the distilled water, the ionic conductance is minimum among the all liquid forms of water.

Q.7. The anodic half-cell of lead-acid battery is recharged using electricity of 0.05 Faraday. The amount of PbSO4 electrolyzed (in gm) during the process is: (Molar mass of PbSO4 = 303 g mol-1)    (2019)
(1) 22.8
(2) 15.2
(3) 7.6
(4) 11.4
Ans.
(3)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.8. If the standard electrode potential for a cell is 2 V at 300 K, the equilibrium constant (K) for the reaction
Zn(s) + Cu2+ (aq) ⇌ Zn2+ (aq) + Cu(s)
at 300 K is approximately
(R= 8JK-1 mol-1, F= 96000 C mol-1)    (2019)
(1) e-80
(2) e-160
(3) e320
(4) e160
Ans.
(4)
We know that, Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
After putting the given values, we get
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
∴ K = e160

Q.9. In the cell
Pt(s)|H2(g, lbar) / HCl(aq)||AgCl(s)/Ag(s)|Pt(s), the cell potential is 0.92 V when a 10-6 molal HCl solution is used. The standard electrode potential of (AgCl/Ag, Cl-) electrode is:    (2019)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(1) 0.94 V
(2) 0.76 V
(3) 0.40 V 
(4) 0.20 V
Ans.
(4)
Given that:
Pt(s)|H2(g, lbar) / HCl(aq)||AgCl(s)/Ag(s)|Pt(s)
Ecell = 0.92 V
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Net cell reaction:
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.10. For the cell Zn(s) | Zn2+(aq) || Mx+ (aq) | M(s), different half cells and their standard electrode potentials are given below:
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
IfPrevious year Questions (2016-20) - Electrochemistry Notes | EduRev, which cathode will give a maximum value of E°cell per electron transferred?    (2019)
(1) Ag+/Ag
(2) Fe3+/Fe2+
(3) Au3+/Au
(4) Fe2+/Fe
Ans.
(1)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.11. Given the equilibrium constant:
KC of the reaction:
Cu(s) + 2Ag+ (aq) → Cu2+ (aq) + 2Ag(s) is
10 x 1015. Calculate the E°cell of this reaction at 298 K.    (2019)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(1) 0.04736 mV
(2) 0.4736 mV
(3) 0.4736 V
(4) 0.04736 V
Ans.
(3)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.12. The standard electrode potential E° and its temperature coefficient Previous year Questions (2016-20) - Electrochemistry Notes | EduRev for a cell are 2 V and -5 x 10-4 VK-1 at 300 K respectively. The cell reaction is:
Zn(s) + Cu2+(aq) → Zn2+ (aq) + Cu
The standard reaction enthalpy (ΔrH°) at 300 K in kJ mol-1 is,
[Use R= 8 JK-1 mol-1 and F = 96,000 C mol-1]    (2019)
(1) -412.8
(2) -384.0
(3) 192.0
(4) 206.4
Ans. 
(1)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.13. Λ0m for NaCl, HCl and NaA are 126.4, 425.9 and 100.5 cm2 mol-1, respectively. If the conductivity of 0.001 M HA is 5 x 10-5 Scm-1, degree of dissociation of HA is:    (2019)
(1) 0.50
 (2) 0.25
(3) 0.125
(4) 0.75
Ans. 
(3)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.14. Given thatPrevious year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
The strongest oxidising agent is:    (2019)
(1) Au3+ 
(2) O2
(3) S2O82- 
(4) Br2
Ans.
(3)
More positive is the reduction potential stronger is the oxidising agent. Reduction potential is maximum for S2O82-. Therefore, it is the strongest oxidising agent amongst the given species.

Q.15. Calculate the standard cell potential (in V) of the cell in which following reaction takes place:
Fe2+ (aq) + Ag+ (aq) → Fe3+ (aq) + Ag(s)
Given that    (2019)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev 
(1) x - z
(2) x - y
(3) x + 2y - 3z 
(4) x + y - z
Ans.
(3)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev (given)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.16. The standard Gibbs energy for the given cell reaction in kJ mol-1 at 298 K is:
Zn(s) + Cu2+ (aq) → Zn2+ (aq) + Cu(s),
E° = 2 V at 298 K
(Faraday's constant, F = 96000 C mol-1)    (2019)
(1) - 384
(2) 384
(3) 192
(4) - 192
Ans.
(1)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
= -2 (96000) 2 V = - 384000 J/mol
= -384 kJ/mol

Q.17. A solution of Ni (NO3)2 is electrolysed between platinum electrodes using 0.1 Faraday electricity. How many moles of Ni will be deposited at the cathode?    (2019)
(1) 0.05
(2) 0.20
(3) 0.15
(4) 0.10
Ans.
(1)
According to the Faraday’s law of electrolysis, nF of current is required for the deposition of 1 mol According to the reaction,
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
2 F of current deposits = 1 mol
∴ 0.1 F of current deposits = 0.1/2 = 0.05 mol

Q.18. Consider the statements S1 and S2 :
S1 : Conductivity always increases with decrease in the concentration of electrolyte.
S2 : Molar conductivity always increases with decrease in the concentration of electrolyte.
The correct option among the following is:    (2019)
(1) Both S1 and S2 are wrong
(2) S1 is wrong and S2 is correct
(3) Both S1 and S2 are correct
(4) S1 is correct and S2 is wrong
Ans.
(2)
Conductivity of an electrolyte is the conductance of 1 cm3 of the given electrolyte. It increases with the increase in concentration of electrolyte due to increase in the number of ions per unit volume. Molar conductivity (λm) is the conductance of a solution containing 1 mole of the electrolyte. It increases with the decrease of concentration due to increase in the total volume having one mole of electrolyte. Thus, interionic attraction increases and degree of ionisation decreases. Therefore, (S1) is wrong and (S2) is correct.

Q.19. Which one of the following graphs between molar conductivity (Λm) versus √C is correct?    (2019)
(1) Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

(2) Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(3) Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
(4) Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Ans. (2)
Both NaCl and KCl are strong electrolytes and as Na+(aq⋅) has less conductance than K+(aq⋅) due to more hydration. Therefore, the graph of option (2) is correct.

Q.20. Given :
Co3+ + e- → Co2+; E° = + 1.81 V
Pb4+ + 2e- → Pb2+; E° = + 1.67 V
Ce4+ + e- → Ce3+; E° = + 1.61 V
Bi3+ + 3e- → Bi; E° = + 0.20 V
oxidizing power of the species will increase in the order:    (2019)
(1) Ce4+ < Pb4+ < Bi3+ < Co3+
(2) Bi3+ < Ce4+ < Pb4+ < Co3+
(3) Co3+ < Ce4+ < Bi3+ < Pb4+
(4) Co3+ < Pb4+ < Ce4+ < Bi3+
Ans. 
(2)
Higher the reduction potential, higher will be oxidising power. So, Bi3+ < Ce4+ < Pb4+ < Co3+

Q.21. How long (approximate) should water be electrolysed by passing through 100 amperes current so that the oxygen released can completely burn 27.66 g of diborane?    (2018)
(Atomic weight of B = 10.8 u)
(1) 6.4 hours
(2) 0.8 hours
(3) 3.2 hours
(4) 1.6 hours
Ans.
(3)
B2H6 + 3O2 →  B2O3 + 3H2O
According to balanced equation:
27.66 g B2H6 i.e. 1 mole B2H6 requires 3 mole of O2. Now this oxygen is produced by electrolysis of water.
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
1 mole O2 is produced by 4 F charge
∴ 3 mole O2 will be produced by 12 F charge
∴ Now applying
Q = It
12 x 96500 C = 100 x t(s)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
t = 3.2 hours

Q.22. When an electric current is passed through acidified water, 112 mL of hydrogen gas at N.T.P. was collected at the cathode in 965 seconds. The current passed, in ampere, is:    (2018)
(1) 0.1
(2) 0.5
(3) 1.0
(4) 2.0
Ans.
(3)

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Q.23. When 9.65 ampere current was passed for 1.0 hour into nitrobenzene in acidic medium, the amount of p-aminophenol produced is:    (2018)
(1) 109.0 g
(2) 98.1 g
(3) 9.81 g
(4) 10.9 g
Ans.
(3)

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

(v.f.) = 4 Previous year Questions (2016-20) - Electrochemistry Notes | EduRev Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

W = 9.81 g


Q.24. Given
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Among the following, the strongest reducing agent is    (2017)
(1) Cr
(2) Mn2+
(3) Cr3+
(4) Cl-
Ans.
(1)

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Positive E° is for Cr, hence it is strongest reducing agent.


Q.25. Consider the following standard electrode potentials (E° in volts) in aqueous solution:
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev
Based on these data, which of the following statements is correct?    (2017)
(1) Tl3+ is more stable than Al3+
(2) Al+ is more stable than Al3+
(3) Tl3+ is more stable than Al+
(4) Tl+ is more stable than Al+
Ans. 
(4)

ΔG is -ve


Q.26. What is the standard reduction potential (E°) for Fe3+ → Fe?
Given that:    (2017)
Previous year Questions (2016-20) - Electrochemistry Notes | EduRev 
(1) –0.057 V
(2) + 0.30 V
(3) – 0.30 V
(4) + 0.057 V
Ans. 
(1)

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

(i) Fe2+ + 2e- → Fe; E° = -0.47V;

(ii) Fe3+ + e- → Fe2+; E° = +0.77V;

(iii) Fe3+ + 3e- → Fe

ΔG° = -nFE° = -2(-0.47)F = 0.94F

ΔG° = -nFE° = -1(-0.77)F = 0.77F

On adding : ΔG° = +0.17F

ΔG° = -nFE°

E° for (Fe3+ → Fe)

= Previous year Questions (2016-20) - Electrochemistry Notes | EduRev 


Q.27. To find the standard potential of M3+/M electrode, the following cell is constituted: Pt/M/M3+ (0.001 mol L-1)/Ag+ (0.01 mol L-1)/Ag
The emf of the cell is found to be 0.421 volt at 298 K. The standard potential of half reaction M3+ + 3e- → M at 298 K will be: (Given EΘAg+/ Ag at 298 K = 0.80 volt)    (2017)
(1) 0.38 volt
(2) 1.28 volt
(3) 0.32 volt
(4) 0.66 volt
Ans.
(3)

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev


Q.28. Galvanization is applying a coating of:    (2016)
(1) Pb
(2) Cr
(3) Cu
(4) Zn
Ans. 
(4)

Galvanization is applying a coating of zinc.

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev


Q.29. What will occur if a block of copper metal is dropped into a beaker containing a solution of 1M ZnSO4?    (2016)
(1) The copper metal will dissolve and zinc metal will be deposited.
(2) The copper metal will dissolve with evolution of oxygen gas.
(3) The copper metal will dissolve with evolution of hydrogen gas.
(4) No reaction will occur.
Ans.
(4)

If a block of copper metal is dropped into a beaker containing solution of 1 M ZnSO4, no reaction will occur because

Previous year Questions (2016-20) - Electrochemistry Notes | EduRev

Hence Cu can't displace Zn from ZnSO4 solution.


Q.30. Identify the correct statement:    (2016)
(1) Corrosion of iron can be minimized by forming an impermeable barrier at its surface.
(2) Iron corrodes in oxygen-free water.

(3) Iron corrodes more rapidly in salt water because its electrochemical potential is higher.
(4) Corrosion of iron can be minimized by forming a contact with another metal with a higher reduction potential.
Ans. 
(1)

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