A. Very Short-Answer Questions
1. What is electrochemistry?
2. Redox reaction involve the transfer of electrons, yet there is no flow of current. Why is this so?
3. How is the flow of electric current in a metal wire different from that in a solution of an electrolyte?
4. What are electrodes?
5. What is galvanic cell?
6. Is the reaction occurs in a galvanic cell spontaneous or nonspontaneous?
7. What is an anode?
8. Which electrode, cathode or anode is the positive pole in a galvanic cell?
9. How much is 1 faraday of charge?
10. Write the cell reaction of the Daniell cell for the passage of 1 faraday of charge.
11. How much of moles of Cu is deposited on the cathode for the passage of 965 C of charge in a Daniell cell?
12. What is the standard emf?
13. In the hydrogen-oxygen galvanic cell, which electrode is the anode?
14. What is the reversible cell?
15. Write the line notation of the Daniell cell.
16. Write the cell diagram for the cell reaction Mg + ZnSO4 → MgSO4 + Zn.
17. How is the equilibrium constant of a reversible cell reaction related to the standard emf of the cell?
18. What is standard hydrogen electode?
19. In a table of reduction potentials, the electrode potentials decreases as one goes up. Where are the strongest reducing agents- at the bottom or at the top? Are they at the left or the right of the half-reactions?
20. What is a concentration cell?
21. What is electrolysis?
22. Why is a CaCl2 + NaCl mixture taken for the electrolysis of molten NaCl?
23. Why does water need to be made alkaline or acidic to carry out electrolysis?
24. The electrolysis of aqueous AgNO3 does not evolve H2 gas at the cathode. Why?
25. How is the eqivalent weight of KMnO4 related to its formula weight in the change
MnO4- → Mn2+?
26. How many coulombs of charge is required for the deposition of 1 mole of Al in the electrolysis of molten Al2O3?
27. What is conductivity?
28. What is molar conductivity?
29. How is equivalent conductivity of Fe2(SO4)3 related to its molar conductivity?
B. Short-Answer Questions
1. What are differences between a chemical and electrochemical reaction?
2. What is a salt bridge?
3. The standard hydrogen-oxygen cell (E0cell=1.23V) and standard Daniell cell (EOcell = 1.10V) are connected in parallel. What are the cell reaction in the two cell?
4. What is electrode potentials?
5. How is the emf of a cell related to the electrode potentials?
6. What are oxidation and reduction potentials?
7. How can be the standard potential of an electrode be determined?
8. Cs has a lower ionization than Li, showing a stronger tendency to get oxidized to Cs+. Why then is the oxidation potential of Cs lower than that of Li?
9. A chemistry textbook says, “An oxidant will spontaneously oxidize a reductant placed lower than it in the table of reduction potentials”. Do you expect to find the half-reaction
Li+ + e- → Li at the lower end or the higher end of the table in the book?
10. How is the electrode potential of a hydrogen related to the pH of the electrolyte solution?
11. What are primary and secondary cells? Give examples of each.
12. What are fuel cell? How they are different from ordinary galvanic cells?
13. What is corrosion?
14. Why do Al and Zn not corrode when exposed to air though they are more reactive than Fe?
15. Explain the corrosion of iron on exposure to air.
16. Why does iron corrode more easily in soda water than ordinary water?
17. What are the different methods of preventing the rusting of iron?
18. What are different types of reaction possible in electrolysis?
19. Why does lead not evolve H2 gas with HCI or H2SO4 solution although the reduction potential of Pb2+ + 2e- → Pb is < 0?
20. What is decomposition voltage?
21. How is the electrolysis of an aqueous solution of NaCI different from the electrolysis of molten NaCI?
22. Why does H2 gas evolve at the cathode in the electrolysis of an aqueous solution of NaCI with platinum cathodes?
23. Why does O2 gas evolve at the anode in the electrolysis of a dilute aqueous solution of NaCI, but CI2 evolve in that of a concentrated solution of NaCI?
24. H2 does not evolve if Hg is used as the cathode in the electrolysis of aqueous NaCI. Explain.
25. How does the electrolysis of aqueous AgNO3 change with change in electrodes from Pt to Ag?
26. What are Faraday’s law of electrolysis?
27. Why do electron not conduct electricity in an aqueous solution?
28. What are electrolytic conductors?
29. What is the cell constant? How is the cell constant of a conductance cell usually determined?
30. What are different units of conductivity and molar conductivity?
31. How does the conductivity of an electrolyte change with concentration?
32. Why does the conductivity of an electrolyte decrease after reaching a peak as concentration increases?
33. What is molar conductance at infinite dilution? How is it determined for strong electrolytes?
34. Why is it not possible to determine the molar conductivity at infinite dilution of a weak electrolyte the same way as that of a strong electrolyte?
35. What is Kohlrausch’s law of independent migration of ions? Explain with examples.
36. How can the molar conductivity at infinite dilution (of electrolytes) be determined applying the law of independent migration of ions?
C. Long-Answer Questions
1. Write cell diagram for the following cell reactions. In each case write the electrode reactions
(a) Mg(s) + 2Ag+(aq) → Mg2+(aq) + 2Ag(s)
(b) Cd(s) + CI2(g) → Cd2+(aq) + 2CI-(aq)
(c) H2(g) + Br2(I) → 2H+(aq) + 2Br-(aq)
2. What is E0cell for the following cells?
(i) Zn I Zn2+ II Sn2+ I Sn
(ii) Ni I Ni2+ II Cu2+ I Cu
Also, write the cell reaction for each cell.
3. Use the data and predict whether the following skeleton equations represent spontaneous reactions. Complete and balance the spontaneous reactions.
(i) Ag+ + Fe2+ → Ag + Fe3+
(ii) H2O2 + Ag+ → Ag + O2
(iii) PbO2 + CI- → Pb2+ + CI2
(iv) I- + NO3- → I2 + NO
4. Indicate whether the following half cells would behave as anodes or cathodes of the galvanic cells formed with a standard hydrogen electrode.
(i) PbIPb2+ (1.00 M)
(ii) PtIFe3+ (0.010 M), Fe2+(0.010 M)
(iii) SnISn2+ (1.0x10-4 M)
(iv) AgIAgBr (satd.) Br-(1.00 M)
5. Indicate the direction of the following reactions. Unless specified otherwise, assume that all substances in solution are initially at a concentration of 1.00 M.
(i) Sn4+ + 2Fe2+ → Sn2+ + 2Fe3+
(ii) Sn2+ + Pb → Sn + Pb2+
(iii) Sn2+(0.01 M) + Pb → Sn + Pb2+(0.0001)
(iv) 4Co3+ + 2H2O → 4Co2+ + O2 + 4H+
D. Numericals
D. Numericals
1. Certain quantity of current is passed through 2 voltameters connected in series and containing XSO4 and Y2SO4 respectively. If the atomic masses of X and Y are in the ratio of 2:1 the ratio of the masses of Y liberated to that of X? [1:1]
2. The equivalent conductivities at infinite dilution of the cation and the anion of a salt A2B are 140 and 80 ohm-1cm2eq-1 respectively. The equivalent conductivity of the salt at infinite dilution is? [120 ohm-1cm2eq-1]
3. When an electric current is passed through acidulated water, 112 mL of hydrogen gas at STP collects at the cathode in 965 seconds. The current passed in amperes is?
2. The equivalent conductivities at infinite dilution of the cation and the anion of a salt A2B are 140 and 80 ohm-1cm2eq-1 respectively. The equivalent conductivity of the salt at infinite dilution is? [120 ohm-1cm2eq-1]
3. When an electric current is passed through acidulated water, 112 mL of hydrogen gas at STP collects at the cathode in 965 seconds. The current passed in amperes is?
4. Find the charge in coulomb on 1 g-ion of N3-. [2.89x105 C]
5. Exactly 0.4 faraday electric charge is passed through three electrolytic cells in series, first containing AgNO3, second CuSO4 and third FeCl3 solution. How many grams of each metal will be deposited assuming only cathodic reaction in each cell? [43.2g,12.7g, 7.47g]
6. A 100 watt, 100 V incandescent lamp is connected in series with an electrolytic cell containing cadmium sulphate solution. What mass of cadmium will be deposited by the current flowing for 10 hours? [19.0598g]
7. How long has a current of 3 ampere to be applied through a solution of silver nitrate to coat a metal surface of 80cm2 with 0.005cm thick layer? Density of silver is 10.5g/cm3. [125.09 s]
8. 0.2964 g of copper was deposited on passage of a current of 0.5 ampere for 30 minutes through a solution of copper sulphate. Calculate the atomic mass of copper. [63.56]
9. 19 g of molten SnCI2 is electrolysed for some time using inert electrodes until 0.119 g of Sn is deposited at the cathode. No substance is lost during electrolysis. Find the ratio of the masses of SnCI2:SnCI4 after electrolysis. (At. mass of Sn=119) [71.34:1]
10. A current of 2.68 ampere is passed for one hour through an aqueous solution of copper sulphate using copper electrodes. Calculate the change in mass of cathode and that of the anode. (At. mass of copper = 63.5). [3.174g, 3.174g]
11. An ammeter and a copper voltameter are connected in series through which a constant current flows. The ammeter shows 0.52 ampere. If 0.635 g of copper is deposited in one hour, what is the percentage error of the ammeter? (At. mass of copper = 63.5) [2.985%]
12. A current of 3.7 ampere is passed for 6 hours between platinum electrodes in 0.5 litre of a 2M solution of Ni(NO3)2. What will be the molarity of the solution at the end of lectrolysis? What will be the molarity of solution if nickel electrodes are used? (Ni = 58.7) [1.72M, 2M]
12. A current of 3.7 ampere is passed for 6 hours between platinum electrodes in 0.5 litre of a 2M solution of Ni(NO3)2. What will be the molarity of the solution at the end of lectrolysis? What will be the molarity of solution if nickel electrodes are used? (Ni = 58.7) [1.72M, 2M]
13. An acidic solution of Cu2+ salt containing 0.4 g of Cu2+ is electrolysed until all the copper is deposited. The electrolysis is continued for seven more minutes with volume of solution kept at 100 mL and the current at 1.2 amp. Calculate the gases evolved at STP during the entire electrolysis.[158.3 mL]
14. Calculate the electricity that would be required to reduce 12.3 g of nitrobenzene to aniline, if the current efficiency for the process is 50 per cent. If the potential drop across the cell is 3.0 volt, how much energy will be consumed? [115800 C, 347.4kJ]
15. After electrolysis of a sodium chloride solution with inert electrodes for a certain period of time, 600 mL of the solution was left which was found to be 1 N in NaOH. During the same period 31.75 g of copper was deposited in the copper voltameter in series with the electrolytic cell. Calculate the percentage theoretical yield of NaOH obtained. [60%]
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