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

Lead storage battery is a type of secondary battery also called as accumulators or storage cells which can be recharged and can be reused as a source of electric current continously. Overall reaction for lead storage battery is: The electrode reactions that occur during discharge, i.e., when the battery is in use are as follows:- At anode: Pb ( s ) + SO 4 2 - ( aq ) → PbSO 4 ( s ) + 2 e - (Oxidation) At cathode: PbO 2 ( s ) + SO 4 2 - ( aq ) + 4 H + ( aq ) + 2 e - → PbSO 4 ( s ) + 2 H 2 O (Reduction) Overall reaction: Pb ( s ) + PbO 2 ( s ) + 4 H + ( aq ) + 2 SO 4 2 - ( aq ) → 2 PbSO 4 ( s ) + 2 H 2 O The electrode reactions that occur during recharge are as follows:- At cathode: PbSO 4 ( s ) + 2 e - → Pb ( s ) + SO 4 2 - ( aq ) (Reduction) At anode: PbSO 4 ( s ) + 2 H 2 O → PbO 2 ( s ) + SO 4 2 - ( aq ) + 4 H + ( aq ) + 2 e - (Oxidation) Overall reaction: 2 PbSO 4 ( s ) + 2 H 2 O → Pb ( s ) + PbO 2 ( s ) + 4 H + ( aq ) + 2 SO 4 2 - ( aq )

Calculate e.m.f. of the following cell at 298 K : 2 Cr ( s ) + 3 Fe 2 + 0 . 01 M → 2 Cr 3 + 0 . 1 M + 3 Fe ( s ) Given : E ( Cr 3 + ∣ Cr ) = − 0 . 74 V E ( Fe 2 + ∣ Fe ) = − 0 . 44 V

The cell reaction is : 2Cr + 3Fe 2+ → 3Fe + 2Cr 3+ To calculate the emf of the cell, we apply the Nernst equation: Where n = number of electrons involved in the cell reaction &there4; n = 6 E ° cell = -0.44-(-0.74) = + 0.30 V Cr 3+ = 0.1M, Fe 2+ = 0.01M (given) By putting R = 8.314 JK -1 mole -1 T = 298K, F = 96500 coulombs We get, E cell = 0.26V Thus, the emf of the cell at 298 K is 0.26 V

Define conductivity of an electrolytic solution. How does it vary with decrease in concentration and why?

Conductivity is the conductance of unit cube of material. S.I unit is S/m. Common unit is S/cm. The conductivity of an electrolytic solution always decreases with decrease in concentration that is on dilution. This is because with dilution, the degree of dissociation increases and the total number of current-carrying ions increases but the number of ions per unit volume decreases.

State Faraday’s first law of electrolysis. How much charge in terms of Faraday is required for the reduction of 1 mol of C u 2 + to C u .

Faraday’s first law of electrolysis states that “the amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolytic solution or melt”. The reduction of one mol of C u 2 + to C u can be represented as: C u 2 + + 2 e - → C u As we can see from the equation that two moles of electron which is equivalent to 2 faraday charge is required for this reaction.

Following reactions occur at the cathode during the electrolysis of aqueous silver chloride. Ag + aq + e - → Ag s ; E ° = + 0 . 80 V H + aq + e - → 1 2 H 2 g ; E ° = + 0 . 00 V On the basis of their standard reduction electrode potential E ° values, which reaction is feasible at the cathode and why?

Given the reaction at the cathode, Ag + aq + e - → Ag s ; E ° = + 0 . 80 V H + aq + e - → 1 2 H 2 g ; E ° = + 0 . 00 V The reaction with a higher value of standard reduction potential E ° is preferred and therefore, the reaction at the cathode during electrolysis is Ag + aq + e - → Ag s .

Define molar conductivity of a solution. Explain how molar conductivity changes with change in concentration of solution for a weak and a strong electrolyte.

Molar conductivity of a solution at a given concentration is the conductance of volume V of a solution containing one mole of electrolyte kept between two electrodes with an area of cross-section A and distance of unit length. Therefore, Λ m = kA l =k. Since l = 1 and A = V (volume containing 1 mole of electrolyte). Λ m = kV . Molar conductivity increases with a decrease in concentration. This is because the total volume, V, of a solution containing one mole of electrolyte also increases. It has been found that a decrease in κ on dilution of a solution is more than compensated by an increase in its volume. Physically, it means that at a given concentration, Λ m can be defined as the conductance of the electrolytic solution kept between the electrodes of a conductivity cell at a unit distance but having an area of cross-section large enough to accommodate sufficient volume of solution that contains one mole of the electrolyte. When concentration approaches zero, the molar conductivity is known as limiting molar conductivity and is represented by the symbol Λ° m. The variation in Λ m concentration is different for strong and weak electrolytes.

What is battery? Give one example each of primary battery and secondary battery.

A battery is a device that stores chemical energy and converts it to electrical energy. Primary batteries are “single use” and cannot be recharged. Dry cells and (most) alkaline batteries are examples of primary batteries. The second type is rechargeable and is called a secondary battery. Examples of secondary batteries include nickel-cadmium (Ni-Cd), lead acid, and lithium-ion batteries.

Depict the galvanic cell in which the reaction takes place. Further show, which of the electrode is negatively charged. Zn s + 2 Ag + aq → Zn 2 + aq + 2 Ag s .

The galvanic cell is an electrochemical cell that uses the transfer of electrons in redox reactions to supply an electric current. Here is the diagram of the galvanic cell that shows the reaction of the cell. Electrons move from anode (zinc electrode) to cathode (silver electrode) in the external circuit. Zinc ions go into the solution at the anode and Ag + ions get deposited at the cathode. Thus, electrons in the external and metal ions in the internal circuit act as carriers of current in. Hence, the overall reaction is obtained by anode and cathode reactions. Zn s + 2 Ag + aq → Zn 2 + aq + 2 Ag s .

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Electrochemistry>Assam Board-2020>Q 13

EASY

12th Assam Board

IMPORTANT

Earn 100

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.

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