CBSE Class 12 Chemistry Electrochemistry Worksheet Set A

1. Give difference between electronic conductance and electrolytic conductance.

2. Define resistivity and give its SI unit.

3. Define conductivity. How does it vary with concentration of an electrolyte?

4. What are super conductors? What types of materials behave as super conductors?

5. NaCl and MgSO₄ have different values of A. Justify.

6. Define over voltage.

7. A mercury cell gives a cell potential of 1.35 V which remains constant during its life. Justify.

8. How much faraday of charge is consumed per 1 mole of H₂SO₄ when lead storage battery is in use?

10. Give relevant points for the following:-

(a) Similarities between galvanic cell and fuel cell

(b) Dissimilarities between galvanic and fuel cell.

(c) Advantages of fuel cell.

(d) Disadvantages of fuel cell.

Important Questions for NCERT Class 12 Chemistry Electrochemistry 

Question. Time required to deposit one millimole of aluminium metal by the passage of 9.65 amperes through aqueous solution of aluminium ion is
(a) 30 s
(b) 10 s 
(c) 30,000 s
(d) 10,000 s 

Question. Which of the following statements is true for the electrochemical Daniel cell?
(a) Electrons flow from copper electrode to zinc electrode
(b) Current flows from zinc electrode to copper electrode
(c) Cations move toward copper electrode
(d) Cations move toward zinc electrode 

Question. The charge required for the reduction of 1 mol of MnO^4- to MnO₂ is : 

(a) 1F
(b) 3 F
(c) 5F
(d) 6F 

Question. The products formed when an aqueous solution of NaBr is electrolysed in a cell having inert electrodes are: 
(a) Na and Br₂
(b) Na and O₂
(c) H₂ ,Br₂ and NaOH
(d) H₂ and O₂ 

Question. The emf of Daniell cell at 298 K is E₁ Zn | ZnSO₄ (0.01 M) | | CuSO₄ (1.0 M) | Cu When the concentration of ZnSO₄ is 1.0 M and that of CuSO₄ is 0.01 M, the emf changed to E₂
What is the relation between E₁ and E₂?
(a) E₁ = E₂
(b) E₂ = 0 ≠ E₂
(c) E₁ > E₂
(d) E₁ < E₂ 

Question. Equivalent conductance of an electrolyte containing NaF at infinite dilution is 90.1 Ohm^–1cm₂. If NaF is replaced by KF what is the value of equivalent conductance?
(a) 90.1 Ohm^–1cm₂
(b) 111.2 Ohm^–1cm₂
(c) 0
(d) 222.4 Ohm^–1cm₂ 

Question. For a cell reaction involving two electron change, the standard EMF of the cell is 0.295 V at 2°C.
The equilibrium constant of the reaction at 25°C will be
(a) 29.5 × 10^–2
(b) 10
(c) 1 × 10¹⁰
(d) 2.95 × 10^–10 

Question. A 0.5 M NaOH solution offers a resistance of 31.6 ohm in a conductivity cell at room temperature. What shall be the approximate molar conductance of this NaOH solution if cell constant of the cell is 0.367 cm^–1.
(a) 234 S cm₂ mole^–1
(b) 23.2 S cm₂ mole^–1
(c) 4645 S cm₂ mole^–1
(d) 5464 S cm₂ mole^–1 

Question. The cell constant of a given cell is 0.47 cm^–1. The resistance of a solution placed in this cell is measured to be 31.6 ohm. The conductivity of the solution (in S cm^–1 where S has usual meaning) is 
(a) 0.15
(b) 1.5
(c) 0.015
(d) 150 

Question. The standard reduction potentials at 298K for the following half reactions are given against each
Zn²⁺ (aq) + 2e ⇌ Zn(s) ; –0.762 V
Cr³⁺ (aq) + 3e ⇌ Cr (s); –0.740 V
2H+ (aq) + 2e ⇌ H2 (g) ; 0.00 V
Fe3+ (aq) + e ⇌ Fe²⁺ (aq) ;0.770 V
Which is the strongest reducing agent? 
(a) Zn (s)
(b) Cr (s)
(c) H2(g)
(d) Fe3+ (aq) 

Question. A hydrogen electrode is immersed in a solution with pH = 0 (HCl). By how much will the potential (reduction) change if an equivalent amount of NaOH is added to the solution.
(Take H2 p = 1 atm), T = 298 K. 
(a) increase by 0.41 V
(b) increase by 59 mV
(c) decrease by 0.41 V
(d) decrease by 59 mV 

ONE MARK QUESTIONS

1. What is meant by limiting molar conductivity? 

2. The E^ values of Cu and Zn are 0.34V and –0.76V respectively. Which of the two is a stronger reducing agent?

3. How many faradays are required to produce 2.4g of Mg?

4. How much charge is needed to oxidize one mole of FeO to Fe₂O₃?

TWO MARK QUESTIONS

1. Define and express the relationship between conductivity and molar conductivity for the solution of an electrolyte.

2. Electrolytic specific conductance of 0.25M solution of KCl at 25⁰C is 2.56 x 10-2S/cm, calculate the molar conductance.

3. Describe the reactions which occur at the electrodes in a fuel cell that causes H² and O₂ to produce electricity.

4. How many hours does it take to reduce 3 moles of Fe³⁺ to Fe²⁺ with a current of 2amps?

5. Account for the following:

a) Alkaline medium inhibits the rusting of iron.

b) Iron does not rust even if the zinc coating is broken in a galvanized iron pipe. 

THREE MARK QUESTIONS

1. Three electrolytic cells A, B, C containing solutions of ZnSO₄, AgNO₃ and CuSO₄, respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited? 

2. Conductivity of 0.00241 M acetic acid is 7.896 × 10^–5 S cm^–1. Calculate its molar conductivity and if λ0mfor acetic acid is 390.5Scm² mol^–1, what is its dissociation constant?

3. Calculate the equilibrium constant and ΔG⁰ for the following reaction at 25⁰C. Ni(s)+ 2Ag⁺(aq) → Ni²⁺(aq) + 2Ag (s), Given that the cell potential at 25⁰C is 1.05V. (1F = 96500 C mol^-1) 

4. What type of a battery is the lead storage battery? Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery when the cell is in use.

5. A conductivity cell with cell constant 3cm^-1 is filled with 0.1M acetic acid solution. The resistance is found to be 4000 ohms.
Find a] molar conductance of 0.1M acetic acid
b] Degree of dissociation of acetic acid given that ∧⁰ (CH₃COOH) = 400 S cm² mol^-1.

FIVE MARK QUESTIONS

1. a) State Kohlrausch law of independent migration of ions. Write an expression for the molar conductivity of acetic acid at infinite dilution according to Kohlrausch law.

b) Calculate λ0m for acetic acid. Given that λ0m (HCl) = 426 Scm²mol^-1 and λ⁰m (CH₃COONa) = 91 Scm²mol^-1

VALUE BASED QUESTION

1. Ram lives at the second floor. He is painting the iron stair ways of his house to preventing it from corrosion.
a) What do you mean by corrosion?
b) How can you prevent corrosion?
c) What values are displayed by Ram?
d) Write the reaction occurring during corrosion.

Important Questions for NCERT Class 12 Chemistry Electrochemistry 

Question. A hypothetical electrochemical cell is shown below : A/ A+ (x M)||B+(y M)|B
The emf measured is + 0.20 V. The cell reaction is
(a) A + B⁺ → A+ + B
(b) A⁺ + B → A + B+
(c) A⁺ + e– → A; B⁺ + e^– → B
(d) the cell reaction cannot be predicted. 

Question. E°Fe²⁺/Fe = – 0.441 V and E°Fe³⁺/Fe²⁺ = 0.771 V, the standard EMF of the reaction Fe + 2Fe³⁺ → 3Fe²⁺ will be
(a) 0.111 V
(b) 0.330 V
(c) 1.653 V
(d) 1.212 V 

Question. Standard electrode potentials are Fe2+/Fe;
E° = –0.44 and Fe³⁺/Fe²⁺; E° = 0.77. Fe²⁺, Fe³⁺ and Fe blocks are kept together, then
(a) Fe³⁺ increases (b) Fe3+ decreases
(c) Fe²⁺/Fe³⁺ remains unchanged
(d) Fe²⁺ decreases. 

Question. Electrode potential for the following half-cell reactions are
Zn → Zn²⁺ + 2e–; E° = + 0.76 V;
Fe → Fe2+ + 2e–; E° = + 0.44 V.
The EMF for the cell reaction
Fe²⁺ + Zn → Zn²⁺ + Fe will be
(a) – 0.32 V
(b) + 1.20 V
(c) – 1.20 V
(d) + 0.32 V

Question. An electrochemical cell is set up as :
Pt; H₂ (1 atm)|HCl(0.1 M) || CH₃COOH (0.1 M) |H₂ (1 atm); Pt. The e.m.f. of this cell will not be zero, because
(a) acids used in two compartments are different
(b) e.m.f. depends on molarities of acids used
(c) the temperature is constant
(d) pH of 0.1 M HCl and 0.1 M CH₃COOH is not same. 

Question. Standard reduction potentials at 25°C of Li+|Li, Ba²⁺|Ba, Na⁺|Na and Mg²⁺|Mg are –3.05, –2.90,–2.71 and –2.37 volt respectively. Which one of the following is the strongest oxidising agent?
(a) Ba²⁺
(b) Mg²⁺
(c) Na⁺
(d) Li⁺ 

Question. A solution of potassium bromide is treated with each of the following. Which one would liberate bromine?
(a) Hydrogen iodide
(b) Sulphur dioxide
(c) Chlorine
(d) Iodine

Question. For the cell reaction :
2Fe³⁺_(aq) + 2I–(aq) 2Fe²⁺_(aq) + I_2(aq)
E°_cell = 0.24 V at 298 K. The standard Gibbs’ energy (ΔrG°)of the cell reaction is
[Given that Faraday constant, F = 96500 C mol^–1]
(a) 23.16 kJ mol^–1
(b) –46.32 kJ mol^–1
(c) –23.16 kJ mol^–1
(d) 46.32 kJ mol^–1

Question. In the electrochemical cell :
Zn|ZnSO₄₍0.01 M)||CuSO₄(1.0 M)|Cu, the emf of this Daniell cell is E1. When the concentration of ZnSO₄ is changed to 1.0 M and that of CuSO4 changed to 0.01 M, the emf changes to E₂.
From the followings, which one is the relationship between E₁ and E₂? (Given, RT/F = 0.059)
(a) E₁ < E₂
(b) E₁ > E₂
(c) E₂ = 0 ≠ E₁
(d) E₁ = E₂

Question. If the E°cell for a given reaction has a negative value,which of the following gives the correct relationships for the values of ΔG° and Keq ?
(a) ΔG° > 0; K_eq < 1
(b) ΔG° > 0; K_eq > 1
(c) ΔG° < 0; K_eq > 1
(d) ΔG° < 0; K_eq < 1

Question. The pressure of H₂ required to make the potential of H₂ electrode zero in pure water at 298 K is
(a) 10^–10 atm
(b) 10^–4 atm
(c) 10^–14 atm
(d) 10^–12 atm.

Question. A hydrogen gas electrode is made by dipping  platinum wire in a solution of HCl of pH = 10 and by passing hydrogen gas around the platinum wire at one atm pressure. The oxidation potential of electrode would be
(a) 0.118 V
(b) 1.18 V
(c) 0.059 V
(d) 0.59 V 

Question. Consider the half-cell reduction reaction
Mn²⁺ + 2e– → Mn, E° = – 1.18 V
Mn²⁺ → Mn³⁺ + e–, E° = – 1.51 V
The E° for the reaction, 3Mn²⁺ → Mn0 + 2Mn³⁺, and possibility of the forward reaction are respectively
(a) – 4.18 V and yes
(b) + 0.33 V and yes
(c) + 2.69 V and no
(d) – 2.69 V and no.

Question. For the reduction of silver ions with copper metal, the standard cell potential was found to be + 0.46 V at 25 °C. The value of standard Gibbs energy, DG°
will be (F = 96500 C mol^–1)
(a) – 89.0 kJ
(b) – 89.0 J
(c) – 44.5 kJ
(d) – 98.0 kJ 

Question. Given :
(i) Cu²⁺ + 2e– → Cu, E° = 0.337 V
(ii) Cu²⁺ + e– → Cu+, E° = 0.153 V
Electrode potential, E° for the reaction,
Cu⁺ + e– → Cu, will be
(a) 0.90 V
(b) 0.30 V
(c) 0.38 V
(d) 0.52 V 

1. Can you store CuSO₄ solution in Zn pot ?

2. Write the name of electrolyte used in mercury cell.

3. What does the negative value of E⁰_cell indicate?

4. What fiows in the internal circuit of the Galvanic cell?

5. What is the EMF of the cell when the cell reaction attains equilibrium ?

6. Why does an aqueous solution of NaCl in electrolysis give H₂ gas at cathode not sodium metal?

7. Which type of metal can be used in cathodicprotection of iron against rusting?

8. Why does the conductivity of solution decreases on dilution ?

9.Except hydrogen, write the name of two chemical species which are used in fuel cell.

10.How many coulombs are required for conversion of 1 molFeO into Fe₂O₃?

11.State the factors which influences the value of cell potential.

12.What is the relationship between the free energy change and EMF of the cell?

13. What are the products of electrolysis of molten NaCl and aqueous solution of NaCl?

14.What is the role of ZnCl₂ in dry cell?

15.Rusting of iron is quicker in saline than ordinary water.why?

16.Write one use of Kohlrausch’s law.

17.What is cell constant ?

18.What is the relationship between Molar conductivity of electrolytic solution to its degree of dissociation ?

19.Which type of cell is used in wrist watch?

20.Which acid doesnot react with rust?

Answer : 1. No, Zn is more reactive thanCu . 

2. ZnO and KOH

3. Negative value shows reaction is non- spontaneous

4. Ions.

5. E⁰_cell = 0

6. Electrode potential of hydrogen is greater than Na.

7. More reactive metals than Fe. Such as Zn,Mg.

8. Due to less no. of ions oer unit volume.

9. Methane and methanol.

10. 1 faraday

11. Concentration of electrolyte and no. of electron exchanged

12. ΔG⁰ = -nFE⁰

13. Na , Cl₂ and H₂,Cl₂

14. Zn²⁺ ions combines with NH₃ to form complex [Zn(NH₃)₂]²⁺

15. Due to presence of salt in saline water.

16. To find the limiting molar conductivity of weak electrolyte

17. The ratio of l/a

18. α =Λ^c m/Λ⁰m

19. Mercury cell or Button cell

20. Organic acid.

Two marks question:-
1. Consider the standard electrode potential k⁺/K = - 2.93 V, Ag⁺/Ag= 0.80V, Hg²⁺ /Hg = 0.79V Cr³⁺/Cr = -0.74V. arrange these metals in their increasing order of reducing power.
Answer : Ag< Hg<Cr<K

2. The conductivity of 0.20M soiution of HCl at 298K is 0.0248 SCm-1.Calculate molar conductivity.
Answer : Λ⁰_m = K x 1000/M , 124SCm²/mol

3. How much charge will be required for 1 mol Cu²⁺ to Cu and for 1 mol MnO₄^- to Mn²⁺?
Answer : Cu²⁺ + 2e^- → Cu , 2F
MnO4^- + 8H⁺5e^- → Mn²⁺+8H₂O, 5F

4. Write the Variation of conductivity and Molar conductivity with dilution.
Answer : With increase in dilution, conductivity decreases but molar conductivity increases.

5. Λ⁰_m for NaCl ,HCl and NaAc are 126.4,425.9 and 91.0 SCm²/mol respectively .Calculate Λ0m for acetic acid.
Answer : Λ⁰_m (HAc) =λ⁰_H++λ⁰_Ac =λ⁰_H+ +λ⁰_cl- +λ⁰_Ac- +λ⁰_Na+ - λ⁰_cl- - λ⁰_Na+
= (425.9 +91.0 – 126.4) SCm²/mol
= 390.5SCm²/mol

6. A solution of Ni(NO₃)₂ is electrolyzed between Pt electrode using current of 5 amp. For 20 min. What mass of Ni will be deposited at cathode ?
Answer : Q = IT, 6000C. 58.7 x6000/2 x 96500 = 1.825 gm.

7. State and explain Faraday laws of electrolysis.
Answer : Statement and mathematical derivation.

8. Write the cell reaction of Lead storage battery.
Answer : at anode
Pbso₄ +2H₂O → PbO₂ + SO₄^2- + 4H⁺ 2e^-
At cathode
PbSO₄ + 2e^- → Pb + SO₄^2-

9. Which cell is more efficient than others.why?
Answer : Fuel cell, as it has high efficiency and continuous source of energy .pollution free working.

10. Discuss the mechanism of protection of water supply of underground pipe line system.
Answer : More reactive metal is used to follow the principle of sacrificial protection.

Three marks question:-

1. Explain construction and working of standard Hydrogen electrode?

2. What is an electrochemical series? How does it predict the feasibility of a certain redox reaction?

3.The conductivity of an aqueous solution of NaCl in a cell is 92 1-1 cm the resistance offered by this cell is 247.8 . Calculate the cell constant?

4.The measured resistance of a cell containing 7.5 x 10^-3 M solution of KCl at 25⁰C was 1005 calculate
(a) Specific conductance and
(b) Molar conductance of the solution. Cell Constant = 1.25 cm^-1

5.Enlist the factors affecting corrosion?