Modern Science Centre (Research Wing) Institute of Chemical Studies: School of Chemistry

Modern Science Centre (Research Wing) Institute of Chemical Studies: School of Chemistry

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Electrochemistry Tablet 1 Standard Model Papers

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Modern Science Centre (Research Wing): School of Chemistry

ElectrochemistryTablet 1 for ISC XII, CBSE XII, & Competitive Examinations

Nernst Equation

Presented by: Dr. Nishi Saxena

Test- Attempt any 3 Questions: Max Marks = 27, Time allowed = 50 minutes

Name: ______

Class: ______

Date: ______Time allowed: 75 minutes

Question 1 [2+3+2+2]

(i)Consider the following cell

The standard reduction potentials are:

Cu2+ + 2e – Cu; E0 = + 0.35V

Zn2+ + 2e – Zn; E0 = – 0.763V

(a)Write down the cell reaction.

(b)Calculate standard emf of the cell.

(ii)A galvanic cell consists of a metallic zinc plate immersed in 0.1M Zn(NO3)2 solution and a metallic plate of lead immersed in 0.02M solution of Pb(NO3)2

(a)Write the chemical equation for the electrode reactions.

(b)Represent the cell.

(c)Calculate emf of the cell.

Given: E0Zn2+, Zn = – 0.76V; E0Pb2+, Pb = – 0.13V

(iii)Calculate the electrode potential of a copper wire dipped in 0.1M CuSO4 solution at 250C. The standard electrode potential of copper is 0.34 V.

(iv)A zinc rod is dipped in 0.1M solution of ZnSO4. The salt is 95% dissociated at this dilution at 298K. Calculate the electrode potential.

Given: E0Zn2+/ Zn = – 0.76V

Question 2 [3+2+4]

(i)The emf of the following cell is found to be 0.20V at 298K. What is the molar concentration of Cd2+ ions in the solution?

Given: E0Cd2+/Cd = – 0.40V; E0Ni2+/Ni = – 0.25V

(ii)At what pH of solution of HCl will hydrogen gas electrode show electrode potential of – 0.118 V? H2 gas is bubbled at 298K and 1 atm pressure.

(iii)For the cell

(a)Calculate the reduction potential of each electrode if the standard reduction potentials of copper and silver electrodes are 0.34 volts and 0.80 volts respectively.

(b)Calculate emf of the cell.

(c)Write the cell reaction.

(d)Is this reaction spontaneous? Why?

Question 3 [4+3+2]

(i)The standard reduction potentials of cadmium and silver electrodes are – 0.04 volts and 0.08 volts respectively.

(a)Represent the cell where the following reaction takes place:

Cd + 2Ag+ Cd2+ + 2Ag

(b)Calculate the standard emf of this cell.

(c)Calculate the emf of the cell if 0.01M solutions of Cd2+and Ag+are used.

(d)Is the free energy change of the reaction taking place in the above cell positive or negative?

(ii)The standard reduction potentials of copper and zinc electrodes are + 0.350 volts and – 0.763 volts respectively. For the cell

(a)Write the cell reaction.

(b)Calculate emf of the cell.

(c)Is the cell reaction spontaneous? Why?

(iii)The standard reduction potentials of magnesium and silver electrodes are – 2.38 volts and +0.80 volts respectively. A galvanic cell is set up using these two electrodes and equimolar solutions of their ions.

(a)Which will be cathode and which will be anode?

(b)Represent the cell and write the cell reaction.

Question 4 [3+3+3]

(i)Calculate emf of the following cell at 298K:

Given the potential of the calomel electrode is 0.242 volts and the standard

potential of the zinc electrode is – 0.763 volts.

(ii)The standard potentials of Pb/ Pb2+and Pt I –/ I2 are – 0.126 volts and + 0.536 volts respectively. When a galvanic cell is constructed using 0.1 molar concentrations of the respective ions Pt is found to be the cathode. What is the voltage generated in the cell?

(iii)A cell is constructed by dipping a zinc rod in 0.1M zinc nitrate solution and a lead rod in 0.2M lead nitrate solution.

Given: E0Zn2+/Zn = – 0.76V; E0Pb2+/Pb = – 0.13V

(a)Write the spontaneous cell reaction.

(b)Calculate the standard emf and emf of the cell.

Question 5 [3+2+4]

(i)Calculate the potential of the following cell at 250C.

Sn4+ (1.5M) + Zn Zn2+ (0.5M) + Sn2+ (2.0M)

Given: E0Sn4+/Sn2+= 0.13V; E0Zn2+/Zn = – 0.76V

Will the cell potential increase or decrease of concentration of Sn4+ is increased?

(ii)Calculate Ecell for the following reaction at 250C.

Zn + Cu2+ (0.20M) Zn2+ (0.50M) + Cu

Given: E0Zn2+/ Zn = – 0.76V; E0Cu2+/Cu = 0.34V

(iii)For the cell

Given: E0Zn,Zn2+= 0.761V; E0Cu2+, Cu = 0.339V

(a)Write the cell reaction.

(b)Calculate E0 of the cell.

(c)Calculate emf of the cell.

(d)Calculate free energy change at 298K involved in the cell.

Given: Faraday’s constant F = 96500 coulomb eq –1.

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