Chapter 5 electrochemistry class 12 chemistry maharashtra board

    1. Choose the most correct option.

    i. Two solutions have the ratio of their concentrations 0.4 and ratio of their conductivities 0.216. The ratio of their molar conductivities will be
    a. 0.54\

    b. 11.574
    c. 0.0864

    d. 1.852

    Solution

    ii. On diluting the solution of an electrolyte
    a. both ∧ and k increase
    b. both ∧ and k decrease
    c. ∧ increases and k decreases
    d. ∧ decreases and k increases

    Solution

    iii. 1 S m2 mol-1 is eual to 
    a. 10-4 S m2 mol-1
    b. 104 Ω-1 cm2 mol-1
    c. 10-2 S cm2 mol-1
    d. 102 Ω-1 cm2 mol-1

    Solution
    iv. The standard potential of the cell in which the following  reaction occurs H2 (g,1atm) + Cu2⊕(1M) →2H⊕(1M) + Cu (s), (E0 Cu = 0.34V) is a. -0.34 V b. 0.34 V c. 0.17 V d. -0.17 V
    Solution

    v. For the cell, Pb (s)|Pb2⊕(1M)||Ag⊕(1M) |Ag (s), if concentraton of an ion in the anode compartment is increased by a factor of 10, the emf of the cell will

    a. increase by 10 V

    b. increase by 0.0296 V
    c. decrease by 10 V
    d. decrease by 0.0296 V

    Solution

    vi. Consider the half reactions with standard potentials
    i. Ag⊕ (aq) + e Ag (s) →E0 = 0.8V

    ii. I2 (s) + 2e 2I (aq)→ E0 = 0.53V

    iii. Pb2⊕ (aq) + 2e Pb (s)→ E0 = -0.13V

    iv. Fe2⊕ (aq) + 2e Fe (s) →E0 = – 0.44V

    The strongest oxidising and reducing agents respectively are
    a. Ag and Fe2⊕

    b. Ag⊕ and Fe
    c. Pb2⊕ and I

    d. I2 and Fe2⊕

    Solution

    vii. For the reaction Ni(s) + Cu2⊕ (1M)→ Ni2⊕ (1M) + Cu (s), E0 cell =
    0.57V ΔG0 of the reaction is
    a. 110 kJ

    b. -110 kJ
    c. 55 kJ

    d. -55 kJ

    Solution

    viii. Which of the following is not correct?
    a. Gibbs energy is an extensive property
    b. Electrode potential or cell potential is an intensive property.
    c. Electrical work = – ΔG
    d. If half reaction is multiplied by a numerical factor, the corresponding E0 value is also multiplied by the same factor.

    Solution
    ix. The oxidation reaction that takes place in lead storage battery during discharge is a. Pb2⊕ (aq) + SO4 2 (aq)→ PbSO4(s) b. PbSO4 (s) + 2H2O (l) →PbO2 (s) + 4H⊕(aq) + SO4 2 (aq) + 2e c. Pb (s) + SO4 2 (aq) →PbSO4 (s) + 2e d. PbSO4(s) + 2e →Pb(s) + SO4 2 (aq)
    Solution

    x. Which of the following expressions represent molar conductivity of Al2(SO4)3?
    a. 3 λ0 Al3⊕ + 2 λ0 SO4  2
    b. 2 λ0 Al3⊕ + 3 λ0 SO42
    c. 1/3 λ0 Al3⊕ + 1/2 λ0 SO4 2
    d. λ0 Al3⊕ + λ0 SO4 2

    Solution

    2. Answer the following in one or two sentences.

    i. What is a cell constant ?

    Solution

    ii. Write the relationship between conductivity and molar conductivity and hence unit of molar conductivity.

    Solution

    iii. Write the electrode reactions during electrolysis of molten KCl.

    Solution

    iv. Write any two functions of salt bridge.

    Solution
    v. What is standard cell potential for the reaction 2Al(s) + 3Ni2⊕(1M) →2Al3⊕(1M) + 3Ni (s) if E0 Ni = – 0.25 V and E0 Al = -1.66V ?
    Solution

    vi. Write Nerst equation. What part of it represents the correction factor for nonstandard state conditions ?

    Solution

    vii. Under what conditions the cell potential is called standard cell
    potential ?

    Solution

    viii. Formulate a cell from the following electrode reactions :
    Au3⊕(aq) + 3e →Au(s)
    Mg(s) →Mg2⊕(aq) + 2e

    Solutin

    ix. How many electrons would have a total charge of 1 coulomb ?

    Solution

    x. What is the significance of the single vertical line and double vertical line in the formulation galvanic cell.

    Solution

    3. Answer the following in brief

    i. Explain the effect of dilution of solution on conductivity ?

    Solution

    ii. What is a salt bridge ?

    Solutin

    iii. Write electrode reactions for the electrolysis of aqueous NaCl.

    Solution

    iv. How many moles of electrons are passed when 0.8 ampere current is passed for 1 hour through molten CaCl2 ?

    Solution

    v. Construct a galvanic cell from the electrodes Co3⊕|Co and
    Mn2⊕ |Mn. E0 Co = 1.82 V, E0 Mn = – 1.18V. Calculate E0 cell.

    Solution

    vi. Using the relationsip between ΔG0 of cell reaction and the standard potential associated with it, how will you show that the electrical potential is an intensive property ?

    Solution

    viii. Derive the relationship between standard cell potential and
    equilibrium constant of cell reaction.

    Solution

    ix. It is impossible to measure the potential of a single electrode. Comment.

    Solutin

    x. Why do the cell potential of lead accumulators decrease when it
    generates electricity ? How the cell potential can be increased ?

    Solution

    xi. Write the electrode reactions and net cell reaction in NICAD battery.

    Solution

    4. Answer the following :

    i. What is Kohrausch law of independent migration of ions?
    How is it useful in obtaining molar conductivity at zero concentration of a weak electrolyte ? Explain with an example.

    Solution

    ii. Explain electrolysis of molten NaCl.

    Solution

    iii. What current strength in amperes will be required to produce 2.4
    g of Cu from CuSO4 solution in  1 hour ? Molar mass of Cu = 63.5 g
    mol-1. (2.03 A)

    Solution

    iv. Equilibrium constant of the reaction, 2Cu⊕(aq) Cu2⊕(aq) + Cu(s) is 1.2 × 106. What is the standard 119 potential of the cell in which the reaction takes place ? (0.36 V)

    Solution

    v. Calculate emf of the cell Zn(s)|Zn2⊕(0.2M)||H⊕(1.6M)| H2(g, 1.8 atm) |Pt at 250C. (0.785V)

    Solution

    vi. Calculate emf of the following cell at 250C.
    Zn (s) |Zn2⊕(0.08M)||Cr3⊕(0.1M)|Cr E0 Zn = – 0.76 V, E0 Cr = – 0.74 V (0.0327 V)

    Solution

    vii. What is a cell constant ? What are its units? How is it determined
    experimentally?

    Solution

    viii. How will you calculate the moles of electrons passed and mass of
    the substance produced during electrolysis of a salt solution using
    reaction stoichiometry.

    Solution

    ix. Write the electrode reactions when lead storage cell generates electricity. What are the anode and cathode and the electrode reactions during its recharging?

    Solution

    x. What are anode and cathode of H2- O2 fuel cell ? Name the electrolyte used in it. Write electrode reactions and net cell reaction taking place in the fuel cell.

    Solution

    xi. What are anode and cathode for Leclanche’ dry cell ? Write electrode reactions and overall cell reaction when it generates electricity.

    Solution

    xii. Identify oxidising agents and arrange them in order of increasing strength under standard state conditions. The standard potentials are given in parenthesis.
    Al (-1.66V), Al3⊕(-1.66V),Cl2 (1.36V), Cd2⊕(-0.4V), Fe(-0.44V),
    I2(0.54V), Br (1.09V).

    Solution

    xiii. Which of the following species are reducing agents? Arrange them in order of increasing strength under standard state conditions. The standard potentials are given in parenthesis.
    K (-2.93V), Br2(1.09V), Mg(-2.36V), Ce3⊕(1.61V), Ti2⊕(-0.37V), Ag⊕(0.8 V), Ni (-0.23V).

    Solution
    xiv. Predict whether the following reactions would occur spontaneously under standard state conditions. a. Ca (s) + Cd2⊕ (aq)→ Ca2⊕(aq) + Cd(s) b. 2 Br (s) + Sn2⊕ (aq)→ Br2(l) + Sn(s) c. 2Ag(s) + Ni2⊕ (aq)→ 2 Ag⊕ (aq) + Ni (s) (use information of Table 5.1)
    Solution