Chapter 2 : ELECTROCHEMISTRY

Class 12 Chemistry Chapter 3 Electrochemistry Intext Questions and Answers :

3.1 How would you determine the standard electrode potential of the system  ?

3.2 Can you store copper sulphate solutions in a zinc pot?

3.3 Consult the table of standard electrode potentials and suggest three substances that can oxidise ferrous ions under suitable conditions.

3.4 Calculate the potential of hydrogen electrode in contact with a solution whose  is 10.

3.5 Calculate the emf of the cell in which the following reaction takes place:

Given that  

3.6 The cell in which the following reaction occurs:    has  = 0.236 V at 298 K.

Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction.

3.7 Why does the conductivity of a solution decrease with dilution?

3.8 Suggest a way to determine the  value of water.

3.9 The molar conductivity of 0.025 mol  methanoic acid is 46.1 S  . Calculate its degree of dissociation and dissociation constant. Given  349.6 S  and  54.6 S  .

3.10 If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?

3.11 Suggest a list of metals that are extracted electrolytically.

3.12 Consider the reaction: 

What is the quantity of electricity in coulombs needed to reduce 1 mol of  ?

3.13 Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging.

3.14 Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

3.15 Explain how rusting of iron is envisaged as setting up of an electrochemical cell.

Class 12 Chemistry Chapter 3 Electrochemistry Example Questions and Answers :

3.1 Represent the cell in which the following reaction takes place : 

Calculate its   if   .

3.2 Calculate the equilibrium constant of the reaction:     ,

3.3 The standard electrode potential for Daniell cell is 1.1V. Calculate the standard Gibbs energy for the reaction:  

3.4 Resistance of a conductivity cell filled with 0.1 mol  KCl solution is 100  . If the resistance of the same cell when filled with 0.02 mol  KCl solution is 520 Ω , calculate the conductivity and molar conductivity of 0.02 mol KCl solution. The conductivity of 0.1 mol  KCl solution is 1.29 S/m.

3.5 The electrical resistance of a column of 0.05 mol NaOH solution of diameter 1 cm and length 50 cm is  ohm. Calculate its resistivity, conductivity and molar conductivity.

3.6  The molar conductivity of KCl solutions at different concentrations at 298 K are given below:

    /mol            /S

      0.000198              148.61

      0.000309              148.29

      0.000521              147.81

      0.000989              147.09

Show that a plot between  and  is a straight line. Determine the values of  and A for KCl.

3.7 Calculate  for and  from the data given in Table 3.4.

3.8  for NaCl, HCl and NaAc are 126.4, 425.9 and 91.0 S  respectively. Calculate  for HAc.

3.9 The conductivity of 0.001028  acetic acid is  S  . Calculate its dissociation constant if  for acetic acid is 390.5 S  .

3.10  A solution of  is electrolysed for 10 minutes with a current of 1.5 amperes. What is the mass of copper deposited at the cathode ?

Class 12 Chemistry Chapter 3 Electrochemistry Exercise Questions and Answers :

Question 3.1 : 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.

Answer : The correct order, from highest to lowest reactivity,

So, the correct order is: Mg, Al, Zn, Fe, Cu.

[ Magnesium (Mg) - It is the most reactive metal in the list and will displace all the other metals from their salt solutions.

Aluminum (Al) - It will displace copper and metals below it from their salt solutions.

Zinc (Zn) - It will displace copper, iron, and metals below them from their salt solutions.

Iron (Fe) - It will displace copper and metals below it from their salt solutions.

Copper (Cu) - It is the least reactive metal in the list and will not displace any of the other metals from their salt solutions. ]

Question 3.2 Given the standard electrode potentials,  , , , ,

Arrange these metals in their increasing order of reducing power.

Answer : The increasing order of reducing power based on their standard electrode potentials is:

  (Potassium) with E° = – 2.93 V

 (Magnesium) with E° = – 2.37 V

  (Chromium) with E° = – 0.74 V

 (Mercury) with E° = 0.79 V

  (Silver) with E° = 0.80 V

So, the correct order is: < < < <

Question3.3 :  Depict the galvanic cell in which the reaction takes place. Further show:

(i) Which of the electrode is negatively charged ?

(ii) The carriers of the current in the cell.

(iii) Individual reaction at each electrode.

Answer : The galvanic cell with the given reaction can be represented as follows: 

(i) The electrode on the left-hand side, where Zn(s) is located, is negatively charged.

This is because Zn(s) is the anode, and oxidation occurs at the anode, leading to the release of electrons, making it negatively charged.

(ii) The carriers of the current in the cell are the electrons that flow from the Zn(s) electrode (anode) to the Ag(s) electrode (cathode) through the external circuit.

(iii) Individual reactions at each electrode:

At the anode (left electrode):  (Oxidation of Zn to form  ions and release of electrons)

At the cathode (right electrode):  (Reduction of  ions by gaining electrons to form Ag(s) metal)

Question3.4 :  Calculate the standard cell potentials of galvanic cell in which the following reactions take place:

(i) 

(ii) 

Calculate th and equilibrium constant of the reactions.

Solution : (i) Given,   and

For the reaction: 

  (3 electrons per  ion, and 2 electrons per Cr ion) and

 We have,

 

(ii)  Given,   and

For the reaction :  

 

 

 and

Question3.5 :  Write the Nernst equation and emf of the following cells at 298 K:

(i) 

(ii) 

(iii) 

(iv) )

Solution: (i)

The balanced cell reaction:

Here, n = 2 , R = 8.314 j/mol.K , F=96485 c/mol , T = 298 K

  ,

3.6 In the button cells widely used in watches and other devices the following reaction takes place:

Determine  and  for the reaction.

3.7 Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.

3.8 The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S  . Calculate its molar conductivity.

3.9 The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is 1500 . What is the cell constant if conductivity of 0.001M KCl solution at 298 K is  S  .

3.10 The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below:

Concentration / M       0.001     0.010       0.020         0.050         0.100

          1.237     11.85        23.15         55.53       106.74

Calculate  for all concentrations and draw a plot between  and  . Find the value of  .

3.11 Conductivity of 0.00241 M acetic acid is  S  . Calculate its molar conductivity. If   for acetic acid is 390.5 S  , what is its dissociation constant?

3.12 How much charge is required for the following reductions:

(i) 1 mol of  to  ?

(ii) 1 mol of to  ?

(iii) 1 mol of   to   ?

3.13 How much electricity in terms of Faraday is required to produce

(i) 20.0 g of  from molten  ?

(ii) 40.0 g of  from molten  ?

3.14 How much electricity is required in coulomb for the oxidation of

(i) 1 mol of  to ?

(ii) 1 mol of  to  ?

3.15 A solution of  is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of  is deposited at the cathode?

3.16 Three electrolytic cells A,B,C containing solutions of  ,  and  , 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?

3.17 Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible:

(i) (aq) and   (aq)

(ii)   (aq) and (s)

(iii)  (aq) and  (aq)

(iv) (s) and   (aq)

(v)   (aq) and  (aq).

3.18 Predict the products of electrolysis in each of the following:

(i) An aqueous solution of  with silver electrodes.

(ii) An aqueous solution of  with platinum electrodes.

(iii) A dilute solution of  with platinum electrodes.

(iv) An aqueous solution of  with platinum electrodes