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CHAPTER 3: ELECTROCHEMISTRY, 1) State Michael Faraday’s first law of electrolysis., Write its mathematical form., Ans; 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 electrolyte, W = ZQ or W = Zit, 2) State Michael Faraday’s second law of electrolysis., Write its mathematical form., Ans: The amounts of different substances liberated by, the same quantity of electricity passing through the, electrolytic solution are proportional to their chemical, equivalent weights, W1/E1 = W2/E2, 3) State Kohlrausch law of independent migration of, ions. Write any two applications., Ans: The law states that” limiting molar conductivity of, an electrolyte can be represented as the sum of the, individual contributions of the anion and cation of the, electrolyte.”, Uses: (i) Degree of dissociation of weak electrolyte can, be calculated, (ii) Dissociation constant of weak electrolyte can be, determined., (iii) Limiting molar conductivity of weak electrolyte can, be calculated., 4) Define conductivity (specific conductance) and write, its SI unit., Ans: It is a conductance of a material of 1m long and, area of cross section 1m2., SI Unit is Sm-1., 5) Define molar conductance, what is its SI unit?, Ans. It is the conductance due to all the ions in a, solution containing 1 mole of electrolyte. Sm2mol-1, 6) What is corrosion? Write anodic and cathodic, reactions involved in corrosion of Fe. Name any two, methods for prevention of corrosion., Ans: Corrosion is Loss of metal in the form of its oxide or, any other salt form., At anode: 2Fe(s), , ⎯⎯, →, , 2Fe2+ + 4e-, , At cathode: O2 (g) + 4H+(aq) + 4e- ⎯⎯, → 2H2O, Methods: (i) Coating surface with paint or chemicals like, Bisphenol, (ii) Covering metal surface with more reactive metals like, Zn or Mg, , 7) Explain construction and working of standard hydrogen, electrode., Ans: Hydrogen gas at 1 bar pressure is in equilibrium with 1 molar, HCl solution at 298K in the presence of platinum electrode is, called as SHE, Construction: Platinum wire is sealed, in a glass tube, one end is connected, to the external connection and another, end is connected to platinum, electrode coated with platinum black., The glass tube with platinum electrode, is enclosed in an outer jacket with one, inlet at the top to pass hydrogen has, at 1 bar pressure., Working: When hydrogen gas is passed, equilibrium is exist, between adsorbed H2 gas and H+ ions., Half cell reaction,, , 11) What is secondary battery? Explain lead, storage battery with reactions., Ans: The battery which can be recharged and, reused again is called as secondary battery., Ex: lead storage battery. It consists of a lead anode, and a grid of lead packed with lead dioxide (PbO2 ), as cathode. A 38% solution of sulphuric acid is, used as an electrolyte., , ⎯⎯, → PbSO4(s) + 2eAt cathode:PbO2+ SO42-+ 4H+ +2e- ⎯⎯, → PbSO4+ 2H2O, , H+(aq) + e- ⎯⎯, → ½ H2(g), Cell representation,, Pt(s) | H2(g) (1 bar) | H+(aq) (1M), According to the convention the reduction potential of hydrogen, half cell is assigned is zero at all temperatures., 8) What is primary battery? Give an example., Ans: The battery in which reaction occurs only once and after the, use it becomes dead and cannot reused., Ex; Leclanche cell (dry cell) or mercury cell, , At anode; Pb(s) + SO42-(aq), Overall reaction:, Pb + PbO2 + 2H2SO4, , ⎯⎯, → 2PbSO4 + 2H2O, , On charging the battery the reaction is, reversed and PbSO4(s) on anode and cathode is, converted into Pb and PbO2, respectively., 12) What is fuel cell? Explain hydrogen-oxygen fuel, cell. (draw the diagram), Ans: Galvanic cells that are designed to convert the, energy of combustion of fuels like hydrogen,, methane, methanol, etc. directly into electrical, energy are called fuel cells, , ⎯⎯, → 4H2O + 4eAt cathode: O2 + 2H2O + 4e- ⎯⎯, → 4OHAt anode: 2H2 + 4OH-, , 9) Explain Leclanche cell or dry cell. Write one use., Ans; Anode is zinc container; cathode is carbon (graphite) rod with, MnO2. Electrolyte is moist NH4Cl and ZnCl2., , ⎯⎯, → Zn2+ + 2e –, At cathode: MnO2 + NH4 + + e- ⎯⎯, → MnO(OH) + NH3, Reaction at anode: Zn(s), , Voltage is 1.5V and used in tv remotes, clock etc., 10) Calculate the EMF of the cell in which the following reaction takes, place Ni(s) + 2Ag+(0.002M) ⎯⎯, → Ni2+(0.160M) + 2Ag(s) (Given,, , E, , , Cell, , Ans:, , = 1.05V) (solve similar problems on Nernst equation), , Ecell = E, , 0, cell, , 0.0591, 0.160, 0.0591, [Ni 2+ ], =, 1.05, −, log, −, log, 2, (0.002)2, 2, [Ag + ]2, , = 1.05 - (0.02955 × log 4 10 ) = 0.914 V, 4, , 13) Mention any two factors which affect the, conductivity of electrolytic solution., Ans: Factors which affect the conductivity, (i) the nature of the electrolyte added, (ii) temperature, (iii) size of the ions produced and their, solvation, (iv) the nature of the solvent and its viscosity, (v) concentration of the electrolyte