Electrochemistry

Electrochemistry

S.No.	Intext Questions page
1	How would you determine the standard electrode potential of the system Mg2+|Mg?
2	Can you store copper sulphate solutions in a zinc pot?
3	Consult the table of standard electrode potentials and suggest three substancesthat can oxidise ferrous ions under suitable conditions.
4	Calculate the potential of hydrogen electrode in contact with a solution whosepH is 10.
5	Calculate the emf of the cell in which the following reaction takes placeNi(s) + 2Ag+ (0.002 M) → Ni2+ (0.160 M) + 2Ag(s) Given that (cell) EV = 1.05 V
6	The cell in which the following reaction occurs:2Fe3+ (aq) + 2i-(aq) → 2Fe2+(aq)+ I2(s) has 0cell E = 0.236 V at 298 K. Calculatethe standard Gibbs energy and the equilibrium constant of the cell reaction.
7	Why does the conductivity of a solution decrease with dilution?
8	Suggest a way to determine the Λm° value of water.
9	The molar conductivity of 0.025 mol L–1 methanoic acid is 46.1 S cm2 mol–1.Calculate its degree of dissociation and dissociation constant. Given λ0(H+)= 349.6 S cm2 mol–1 and λ0(HCOO–) = 54.6 S cm2 mol–1
10	If a current of 0.5 ampere flows through a metallic wire for 2 hours, then howmany electrons would flow through the wire?
11	Suggest a list of metals that are extracted electrolytically.
12	Consider the reaction:Cr2O72– + 14H+ + 6e– → 2Cr3+ + 8H2OWhat is the quantity of electricity in coulombs needed to reduce 1 mol ofCr2O72–?
13	Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging.
14	Suggest two materials other than hydrogen that can be used as fuels in fuelcells.
15	Explain how rusting of iron is envisaged as setting up of an electrochemical cell.
	Exercises Questions
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.
2	Given the standard electrode potentials, K+/K = –2.93V, Ag+/Ag = 0.80V, Hg2+/Hg = 0.79V Mg2+/Mg = –2.37 V, Cr3+/Cr = – 0.74V Arrange these metals in their increasing order of reducing power.
3	Depict the galvanic cell in which the reaction Zn(s)+2Ag+(aq) →Zn2+(aq)+2Ag(s) 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.
4	Calculate the standard cell potentials of galvanic cell in which the following reactions take place: (i) 2Cr(s) + 3Cd2+(aq) → 2Cr3+(aq) + 3Cd (ii) Fe2+(aq) + Ag+(aq) → Fe3+(aq) + Ag(s)
5	Write the Nernst equation and emf of the following cells at 298 K (i) Mg(s)|Mg2+(0.001M)||Cu2+(0.0001 M)|Cu(s) (ii) Fe(s)|Fe2+(0.001M)||H+(1M)|H2(g)(1bar)| Pt(s) (iii) Sn(s)|Sn2+(0.050 M)||H+(0.020 M)|H2(g) (1 bar)|Pt(s) (iv) Pt(s)|Br2(l)|Br–(0.010 M)||H+(0.030 M)| H2(g) (1 bar)|Pt(s).
6	In the button cells widely used in watches and other devices the following reaction takes place: Zn(s) + Ag2O(s) + H2O(l) → Zn2+(aq) + 2Ag(s) + 2OH–(aq) Determine ΔrG and E for the reaction.
7	Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
8	The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S cm–1. Calculate its molar conductivity.
9	The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is1500 Ω. What is the cell constant if conductivity of 0.001M KCl solution at 298K is 0.146 × 10–3 S cm–1.
10	The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below:Calculate Λ m for all concentrations and draw a plot between Λ m and c½. Find the value of 0 m Λ .
11	Conductivity of 0.00241 M acetic acid is 7.896 × 10–5 S cm–1. Calculate its molarconductivity and if 0 m Λ for acetic acid is 390.5 S cm2 mol–1, what is its dissociationconstant?
12	How much charge is required for the following reductions: (i) 1 mol of Al3+ to Al. (ii) 1 mol of Cu2+ to Cu. (iii) 1 mol of MnO4 – to Mn2+.
13	How much electricity in terms of Faraday is required to produce(i) 20.0 g of Ca from molten CaCl2.(ii) 40.0 g of Al from molten Al2O3.
14	How much electricity is required in coulomb for the oxidation of (i) 1 mol of H2O to O2. (ii) 1 mol of FeO to Fe2O3.
15	A solution of Ni(NO3)2 is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
16	Three electrolytic cells A,B,C containing solutions of ZnSO4, AgNO3 and CuSO4,respectively are connected in series. A steady current of 1.5 amperes was passedthrough them until 1.45 g of silver deposited at the cathode of cell B. How longdid the current flow? What mass of copper and zinc were deposited?
17	Using the standard electrode potentials given in Table 3.1, predict if the reactionbetween the following is feasible:(i) Fe3+(aq) and I–(aq) (ii) Ag+ (aq) and Cu(s)(iii) Fe3+ (aq) and Br– (aq)(iv) Ag(s) and Fe 3+ (aq)(v) Br2 (aq) and Fe2+ (aq).
18	Predict the products of electrolysis in each of the following:(i) An aqueous solution of AgNO3 with silver electrodes.(ii) An aqueous solution of AgNO3with platinum electrodes.(iii) A dilute solution of H2SO4with platinum electrodes.(iv) An aqueous solution of CuCl2 with platinum electrodes.