ELECTROCHEMISTRY

Very Short Answer Type Questions                                             

1.  Why does the conductivity of a solution decrease with dilution?
2.  Suggest a three metals that are extracted electrolytically.
3.  Consider the reaction :  Cr₂O^2-₇ + 14H⁺ + 6e^– → 2Cr⁺ + 7H₂O                                                                                                                                 What is the quantity of electricity in columns needed to reduce 1 mol of Cr₂O^2-₇.
4.  Suggest two materials other than hydrogen can be used as fuels in fuel cells.
5.  Arrange the following metals in the order in which they displace each other   from the solution of their salts.                           Al, Cu, Fe, Mg and Zn.
6.  The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S/cm. Calculate its   molar conductivity.
7.  Express mathematically relationship among the resistance (R) specific   conductivity ?
8.  What is the relationship between the standard EMF of the cell and the equilibrium constant of the cell reaction at 298 K?
9.  Why is it not possible to measure the single electrode potential?
10.  Why does an aqueous solution of NaI on electrolysis give H₂ gas at the Cathode   and not sodium metal?
11.  What is the overall electrochemical reaction taking place in rusting?
12.  Which type of metal can be used in cathodic protection of iron against rusting?
13.  Write Nernst equation for half cell reaction Mⁿ⁺+ne^–→M.
14.  How much charge is required for the reductions of 1 mol of CH₃NO₂ to CH₃NH₂?
15.  Can you store copper sulphate solutions in a zinc pot? Given E^o_Cu²⁺/Cu = 0.34 V E^o_Zn²⁺/Zn = – 0.76 V

Short Answer Type Questions                                                      

1.  Suggest a way to determine the ∧^o_m value of water.
2.  If a current of 0.5 ampere flows through a metallic wire for two hours, then   how  many electrons flow through the wire?
3.  Calculate the potential of a Zn/Zn²⁺ ion electrode in which the [Zn²⁺]=0.001 M.                                                                                 (E^o_Zn²⁺/_Zn = – 0.76 V, R = 8.314 JK^–1 mol^{–   1}, F = 96500 C mol^–1)
4.  Calculate the equilibrium constant for the following reaction at 298 K :                                                                                                           Cu (s) + Cl₂(g) → CuCl₂ (aq)           R = 8.314 JK^–1mol^–1,   E^o_Cu²⁺_/Cu= 0.34 V    = 1.36 V,
5.  Calculate the equilibrium constant of the reaction:                                                                                                                                                          Cu (s) + 2 Ag⁺ (aq) ⇒Cu²⁺   (aq)  + 2 Ag (s) E°_Cell = 0.46 V
6.  What is the effect of temperature on the electrical conductance of                                                                                                                       (i) metallic conductor           (ii) electrolytic conductor.
7.  (a) State the factors that influence the value of cell potential of the following   cell:                                                                                      Mg (s) |Mg²⁺ (aq) ||Ag⁺   (aq)|Ag (s)                                                                                                                                                                                            (b)Write Nernst equation to calculate the cell   potential of the above cell. If Ag⁺ =0.114 Mg²⁺ = 0.1 M.                                           E^o_Ag⁺_/Ag  = 0.8 V E^o_Mg²⁺_/Mg = – 2.37 V
8.  Why does the molar conductance increase on diluting the solution of a weak electrolyte? Electrolytic conductivity of 0.30 M solution of KCl at 295 K is 3.72 x   10^–2 S cm^–1. Calculate its molar conductivity.
9.  The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is   1500 W. What is the cell constant if conductivity of 0.001 M KCl solution at 298K    is 0.146 × 10^–3 S/cm?
10.  With the help of ionic equations describe what happens when                                                                                                                                 (i) pH of a solution of   dichromate ions is raised,                     (ii) potassium manganate is   electrochemically oxidised.
11.  How much electricity in terms of Faraday is required to produce?                                                                                                                     (i) 20.0 g of Ca from molten CaO₂                                                                       (ii) 40.0 g of Al from molten Al₂O₃
12.  Why is a salt bridge or a porous plate not needed in a lead storage battery?

Very Long Answer Type Questions                                                        

1.  What is corrosion? Describe electrochemical phenomenon of rusting of Iron.
2.  Three electrolytic cells A, B and C containing solutions of zinc sulphate, silver   nitrate and copper sulphate, respectively are connected in series. A steady   current of 1.5 ampere was passed through them until 1.45 g of silver were   deposited at the cathode of cell B. How long did the current flow? What mass of   copper and what mass of zinc were deposited in the concerned cells? (Atomic   masses of Ag = 108, Zn = 65.4, Cu = 63.5)
3.  (A) The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K   is 15000W. What is the cell constant, if the conductivity of 0.001 M KCl solution   at 298 K is 0.146 ×10^-3 S cm^-1?                                                                               (B) Predict the products of electrolysis in the following: A solution of H₂SO₄ with    platinum electrodes.
4.  Calculate the pH of the following half cell: Pt(s)|H_2(g)|H₂SO₄ (aq)                                                                                                                     For the cell the oxidation   potential is +0.3V, p H_2(g) =1 atm
5.  Calculate the standard cell potential of the galvanic cell in which the following   reaction takes place: 2 Cr (s) + 3 Cd²⁺ (aq) → 2 Cr³⁺ (aq) + 3 Cd (s)                                                                                                                                                                                                            Also calculate the value of the reaction.                                                                                                                                                                               (Given:  = – 0.40 V and F = 96500 C mol^-1

Long Answer Type Questions                                                                   

1.  (a)  Calculate the emf of the cell Mg(s) | Mg²⁺ (0.1 M) || Cu²⁺ (1 × 10^-3 M) | Cu (s)   Given : E^o Cu² /Cu = + 0.34V,                   E^o Mg²⁺/Mg = – 2.37V                                                                                                                                                                                                                  (b)  Explain with examples the terms weak and strong electrolytes.
2.  (A)  A solution of CuSO₄ is electrolyzed for 16 minutes with a current of 1.5 amperes. What is the mass of copper deposited at the cathode?                                                                                                                                                                                                             (B)  Calculate the equilibrium constant for the reaction : The standard reduction potentials in acidic conditions are 0.77 and 0.54 V respectively for Fe³⁺ | Fe²⁺ and |  couples.