CBSE Class 12 Chemistry 2022 Term 2 Delhi Set 1

Question : 12

Total: 12

SECTION - C

Read the passage given below and answer the questions that follow:
Oxidation-reduction reactions are commonly known as redox reactions. They involve transfer of electrons from one species to another. In a spontaneous reaction, energy is released which can be used to do useful work. The reaction is split into two half reactions. Two different containers are used and a wire is used to drive the electrons from one side to the other and a Voltaic/Galvanic cell is created. It is an electrochemical cell that uses spontaneous redox reactions to generate electricity. A salt bridge also connects to the half cells. The reading of the voltmeter gives the cell voltage or cell potential or electromotive force. If E°‌cell ‌ is positive the reaction is spontaneous and if it is negative the reaction is non-spontaneous and is referred to as electrolytic cell. Electrolysis refers to the decomposition of a substance by an electric current. One mole of electric charge when passed through a cell will discharge half a mole of a divalent metal ion such as Cu2+. This was first formulated by Faraday in the form of laws of electrolysis.
The conductance of material is the property of materials due to which a material allows the flow of ions through itself and thus conducts electricity. Conductivity is represented by k and it depends upon nature and concentration of electrolyte, temperature, etc. A more common term molar conductivity of a solution at a given concentration is conductance of the volume of solution containing one mole of electrolyte kept between two electrodes with the unit area of cross-section and distance of unit length. Limiting molar conductivity of weak electrolytes cannot be obtained graphically.

(a) Is silver plate the anode or cathode?
(b) What will happen if the salt bridge is removed?
(c) When does electrochemical cell behaves like an electrolytic cell?
(d) (i) What will happen to the concentration of
Zn2+‌ and ‌Ag+‌when ‌E‌cell ‌=0.
(ii) Why does conductivity of a solution decreases with dilution?
OR
(d) The molar conductivity of a 1.5M solution of an electrolyte is found to be 138.9Scm2mol−1. Calculate the conductivity of this solution.

Solution:

(a) Silver plate acts as cathode.
(b) Salt bridge permits the flow of current by completing the circuit as well as it maintains the charge balance between anode and cathode by movement of electrons. If the salt bridge is removed no current will flow in the circuit and the voltage will drop to zero.
(c) An electrochemical cell behaves like an electrolytic cell when there is an application of an external opposite potential on the galvanic cell and reaction is not inhibited until the opposing voltage reaches the value 1.1V. At this stage, no current flows through the cell and on increasing the external potential any further the reaction will function in the opposite direction.
E‌ext ‌>E‌cell ‌
(d) (i) When E‌cell ‌=0, an equilibrium condition is reached and the concentration of Zn2+ and Ag+remains same.
(ii) Conductivity of a solution defined as the conductance of ions present in a unit volume of the solution. On dilution, the number of ions per unit volume decreases. Thus, the conductivity of the solution decreases on dilution.
OR
(d) Molar Conductivity ( k )
‌=‌

‌ Conductivity ‌

‌ Concentration ‌

∧m‌=‌

=‌‌

138.9Scm2mol−1×1.5‌mol∕L

1000cm3∕l

‌ Conductivity ‌‌=∧m×C
=‌0.208Scm−1

Go to Question:

Prev Question