Chapter 8

During the electrolysis of \(0.1 \mathrm{M}-\mathrm{CuSO}_{4}\) solution using copper electrodes, a depletion of \(\mathrm{Cu}^{2+}\) occurs near the cathode with a corresponding excess near the anode, owing to inefficient stirring of the solution. If the local concentration of \(\mathrm{Cu}^{2+}\) near the anode and cathode are, respectively, \(0.12 \mathrm{M}\) and \(0.08 \mathrm{M}\), the back EMF developed at \(298 \mathrm{~K}\) is \((\log 1.5\) \(=0.18,2.303 R T / F=0.06)\) (a) \(0.33 \mathrm{~V}\) (b) \(5.4 \mathrm{mV}\) (c) \(2.7 \mathrm{mV}\) (d) \(10.8 \mathrm{mV}\)

The standard reduction potentials in acidic conditions are \(0.77 \mathrm{~V}\) and \(0.53 \mathrm{~V}\), respectively, for \(\mathrm{Fe}^{3+} \mid \mathrm{Fe}^{2+}\) and \(\mathrm{I}_{3}^{-} \mid \mathrm{I}^{-}\) couples. The equilibrium constant for the reaction: \(2 \mathrm{Fe}^{3+}+3 \mathrm{I}^{-} \rightleftharpoons 2 \mathrm{Fe}^{2+}+\mathrm{I}_{3}^{-}\), is \((2.303 R T / F=0.06)\) (a) \(2 \times 10^{8}\) (b) \(10^{8}\) (c) \(10^{4}\) (d) \(10^{-8}\)

The following electrochemical cell has been set up: \(\mathrm{Pt}(\mathrm{s}) \mid \mathrm{Fe}^{3+}, \mathrm{Fe}^{2+}(\mathrm{a}=1) \| \mathrm{Ce}^{4+}\) \(\mathrm{Ce}^{3+}(\mathrm{a}=1) \mid \mathrm{Pt}(\mathrm{s}) ; E^{\circ}\left(\mathrm{Fe}^{3+} \mid \mathrm{Fe}^{2+}\right)=0.77 \mathrm{~V}\) \(E^{\circ}\left(\mathrm{Ce}^{4} \mid \mathrm{Ce}^{3+}\right)=1.61 \mathrm{~V} .\) If an ammeter is connected between the two platinum electrodes, predict the direction of flow of current. Will the current increase on decrease with time? (a) Ce electrode to \(\mathrm{Fe}\) electrode, decrease (b) \(\mathrm{Ce}\) electrode to \(\mathrm{Fe}\) electrode, increase (c) \(\mathrm{Fe}\) electrode to \(\mathrm{Ce}\) electrode, decrease (d) Fe electrode to \(\mathrm{Ce}\) electrode, increase

Lactic acid, \(\mathrm{HC}_{3} \mathrm{H}_{5} \mathrm{O}_{3}\), produced in \(1 \mathrm{~g}\) sample of muscle tissue was titrated using phenolphthalein as indicator against \(\mathrm{OH}^{-}\) ions which were obtained by the electrolysis of water. As soon as \(\mathrm{OH}^{-}\) ions are produced, they react with lactic acid and at complete neutralization, immediately a pink colour is noticed. If electrolysis was made for 1158 s using \(\quad 6\) \(50.0 \mathrm{~mA}\) current to reach the end point, what was the percentage of lactic acid in muscle tissue? (a) \(5.4 \%\) (b) \(2.7 \%\) (c) \(10.8 \%\) (d) \(0.054 \%\)

From the following \(E^{\circ}\) values for the half-cells: (i) \(\mathrm{D} \rightarrow \mathrm{D}^{2+}+2 \mathrm{e}^{-} ; E^{\circ}=-1.5 \mathrm{~V}\) (ii) \(\mathrm{B}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{B} ; E^{\circ}=-0.5 \mathrm{~V}\) (iii) \(\mathrm{A}^{3-} \rightarrow \mathrm{A}^{2-}+\mathrm{e}^{-} ; E^{\circ}=1.5 \mathrm{~V}\) (iv) \(\mathrm{C}^{2+}+\mathrm{e}^{-} \rightarrow \mathrm{C}^{+} ; E^{\circ}=+0.5 \mathrm{~V}\) Which combination of two half-cells would result in a cell with largest potential? (a) \(\mathrm{i}\) and iii (b) \(\mathrm{i}\) and iv (c) iii and iv (d) ii and iv

The electrode through which electrons enter the electrolytic solution is (a) cathode (b) anode (c) may be anode or cathode (d) both, anode and cathode

Which process occurs in the electrolysis of an aqueous solution of nickel chloride at nickel anode? (a) \(\mathrm{Ni} \rightarrow \mathrm{Ni}^{2+}+2 \mathrm{e}^{-}\) (b) \(\mathrm{Ni}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Ni}\) (c) \(2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}\) (d) \(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}\)

If mercury is used as a cathode during the electrolysis of an aqueous \(\mathrm{NaCl}\) solution, the ions discharged at cathode are (a) \(\mathrm{H}^{+}\) (b) \(\mathrm{Na}^{+}\) (c) \(\mathrm{OH}^{-}\) (d) \(\mathrm{Cl}^{-}\)

At \(25^{\circ} \mathrm{C}\), the molar conductance at infinite dilution for HCl solution is \(4.25 \times 10^{-2} \Omega^{-1} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\), while its specific conductance is \(382.5 \Omega^{-1} \mathrm{~m}^{-1}\). If the degree of dissociation is \(90 \%\), the molarity of solution is (a) \(0.9 \mathrm{M}\) (b) \(1.0 \mathrm{M}\) (c) \(0.1 \mathrm{M}\) (d) \(1.1 \mathrm{M}\)

In the electrolytic cell, flow of electrons is from (a) Cathode to anode in solution (b) Cathode to anode through external supply (c) Cathode to anode through internal supply (d) Anode to cathode through internal supply

Electrolytic cell is used to convert (a) Chemical energy to electrical energy (b) Electrical energy to chemical energy (c) Chemical energy to mechanical energy (d) Electrical energy to mechanical energy

\(\begin{array}{llll}\text { The molar conductivity of } & 0.10 & \mathrm{M}\end{array}\) solution of \(\mathrm{MgCl}_{2}\) is \(100 \mathrm{mho} \mathrm{cm}^{2} \mathrm{~mol}^{-1}\), at \(25^{\circ} \mathrm{C}\). A cell with electrodes that are \(1.50 \mathrm{~cm}^{2}\) in surface area and \(0.50 \mathrm{~cm}\) apart is filled with \(0.10 \mathrm{M}-\mathrm{MgCl}_{2}\) solution. How much current will flow when the potential difference between the electrodes is 5 volts? (a) \(0.03 \mathrm{~A}\) (b) \(3.0 \mathrm{~A}\) (c) \(0.15 \mathrm{~A}\) (d) \(15 \mathrm{~A}\)

Faraday's law of electrolysis fails when (a) temperature is increased (b) inert electrodes are used (c) a mixture of electrolytes is used (d) in none of these cases

For \(\mathrm{Na}^{+}\), the value of symbol \(\lambda_{\mathrm{m}}^{\circ}\) is \(50.0 \Omega^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1} .\) The speed of \(\mathrm{Na}^{+}\) ion in the solution, if in the cell, electrodes are \(5 \mathrm{~cm}\) apart and to which a potential of \(19.3\) volt is applied is (a) \(2 \times 10^{-3} \mathrm{~cm} / \mathrm{s}\) (b) \(1 \times 10^{-3} \mathrm{~cm} / \mathrm{s}\) (c) \(2 \times 10^{-4} \mathrm{~cm} / \mathrm{s}\) (d) \(2 \times 10^{-2} \mathrm{~cm} / \mathrm{s}\)

Using same quantity of current, which among \(\mathrm{Na}, \mathrm{Mg}\) and \(\mathrm{Al}\) is deposited more (by mass) during electrolysis of their molten salts? (a) \(\mathrm{Na}\) (b) \(\mathrm{Mg}\) (c) \(\mathrm{Al}\) (d) All in same

The conductivity of a saturated solution of \(\mathrm{AgCl}\) at \(298 \mathrm{~K}\) was found to be \(3.40\) \(\times 10^{-6} \Omega^{-1} \mathrm{~cm}^{-1} ;\) the conductivity of water used to make up the solution was \(1.60\) \(\times 10^{-6} \Omega^{-1} \mathrm{~cm}^{-1} .\) Determine the solubility of \(\mathrm{AgCl}\) in water in mole per litre at \(298 \mathrm{~K}\). The equivalent conductivity of \(\mathrm{AgCl}\) at infinite dilution is \(150.0 \Omega^{-1} \mathrm{~cm}^{-2} \mathrm{eq}^{-1}\). (a) \(1.44 \times 10^{-10}\) (b) \(1.2 \times 10^{-5}\) (c) \(3.33 \times 10^{-5}\) (d) \(1.2 \times 10^{-8}\)

A certain current liberated \(0.50 \mathrm{~g}\) of hydrogen in \(2 \mathrm{~h}\). How many grams of copper can be liberated by the same current flowing for the same time in a copper sulphate solution? \((\mathrm{Cu}=63.5)\) (a) \(12.7 \mathrm{~g}\) (b) \(15.88 \mathrm{~g}\) (c) \(31.75 \mathrm{~g}\) (d) \(63.5 \mathrm{~g}\)

The current efficiency of an electrodeposition of copper metal in which \(9.8 \mathrm{~g}\) of copper is deposited by a current of 3 A for \(10000 \mathrm{~s}\), from aqueous copper sulphate solution, is about (a) \(60 \%\) (b) \(99 \%\) (c) \(92 \%\) (d) \(75 \%\)

The conductivity of saturated solution of \(\mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) is \(1.2 \times 10^{-5} \Omega^{-1} \mathrm{~cm}^{-1} .\) The limiting equivalent conductivities of \(\mathrm{BaCl}_{2}, \mathrm{~K}_{3} \mathrm{PO}_{4}\) and \(\mathrm{KCl}\) are 160,140 and \(100 \Omega^{-1} \mathrm{~cm}^{2} \mathrm{eq}^{-1}\), respectively. The solubility product of \(\mathrm{Ba}_{3}\left(\mathrm{PO}_{4}\right)_{2}\), is (a) \(10^{-5}\) (b) \(1.08 \times 10^{-23}\) (c) \(1.08 \times 10^{-25}\) (d) \(1.08 \times 10^{-27}\)

The electrochemical equivalents of two substances are \(E_{1}\) and \(E_{2}\). The current that must pass to deposit the same amount at the cathodes in the same time must be in the ratio of (a) \(E_{1}: E_{2}\) (b) \(E_{2}: E_{1}\) (c) \(\left(E_{1}-E_{2}\right): E_{2}\) (d) \(E_{1}:\left(E_{2}-E_{1}\right)\)

The same quantity of electricity is passed through one molar solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and one molar solution of \(\mathrm{HCl}\). The amount of hydrogen evolved from \(\mathrm{H}_{2} \mathrm{SO}_{4}\) as compared to that from \(\mathrm{HCl}\) is (a) the same (b) twice as such (c) one half as such (d) dependent on size of electrode

A solution containing \(1.0 \mathrm{M}\) each of \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{AgNO}_{3}, \mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}\) is being electrolysed using inert electrodes. The values of standard electrode potential are: \(\mathrm{Ag}^{+}\left|\mathrm{Ag}=0.80 \mathrm{~V}, \mathrm{Hg}^{2+}\right| \mathrm{Hg}=0.79 \mathrm{~V}\) \(\mathrm{Cu}^{2+}\left|\mathrm{Cu}=0.34 \mathrm{~V}, \mathrm{Mg}^{2+}\right| \mathrm{Mg}=-2.37 \mathrm{~V}\) With increasing voltage, the sequence of deposit of metals on the cathode will be (a) \(\mathrm{Ag}, \mathrm{Hg}, \mathrm{Cu}, \mathrm{Mg}\) (b) \(\mathrm{Mg}, \mathrm{Cu}, \mathrm{Hg}, \mathrm{Ag}\) (c) \(\mathrm{Ag}, \mathrm{Mg}, \mathrm{Cu}\) (d) \(\mathrm{Cu}, \mathrm{Hg}, \mathrm{Ag}\)

During the electrolysis of an aqueous salt solution, the \(\mathrm{pH}\) in the space near one of the electrode was increased and the other one was decreased. The salt solution was (a) \(\mathrm{NaCl}\) (very dilute) (b) \(\mathrm{ZnCl}_{2}\) (c) \(\mathrm{NaCl}\) (Conc.)

Two electrolytic cells, one containing acidified ferrous chloride and another acidified ferric chloride, are connected in series. The mass ratio of iron deposited at cathodes in the two cells will be (a) \(3: 1\) (b) \(2: 3\) (c) \(1: 1\) (d) \(3: 2\)

A galvanic cell is set up from a zinc bar weighing \(100 \mathrm{~g}\) and \(1.0 \mathrm{~L}\) of \(1.0 \mathrm{M}\) copper sulphate solution. How long would the cell run if it is assumed to deliver a steady current of \(1.0 \mathrm{~A} ?(\mathrm{Zn}=65.4)\) (a) \(53.6 \mathrm{~h}\) (b) \(26.8 \mathrm{~h}\) (c) \(81.97 \mathrm{~h}\) (d) \(40.99 \mathrm{~h}\)

In the lead storage battery, the anode reaction is \(\mathrm{Pb}(\mathrm{s})+\mathrm{HSO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O}\) \(\rightarrow \mathrm{PbSO}_{4}(\mathrm{~s})+\mathrm{H}_{3} \mathrm{O}^{+}+2 \mathrm{e}^{-} .\) How many grams of \(\mathrm{Pb}\) will be used up to deliver \(1 \mathrm{~A}\) for \(100 \mathrm{~h}\) ? \((\mathrm{Pb}=208)\) (a) \(776 \mathrm{~g}\) (b) \(388 \mathrm{~g}\) (c) \(194 \mathrm{~g}\) (d) \(0.1 \mathrm{~g}\)

Three faradays of electricity is passed through molten \(\mathrm{Al}_{2} \mathrm{O}_{3}\), aqueous solutions of \(\mathrm{CuSO}_{4}\) and molten \(\mathrm{NaCl}\). The amounts of \(\mathrm{Al}, \mathrm{Cu}\) and \(\mathrm{Na}\) deposited at the cathodes will be in the molar ratio of (a) \(1: 2: 3\) (b) \(3: 2: 1\) (c) \(1: 1.5: 3\) (d) \(6: 3: 2\)

The number of Faradays required to produce 1 g-atom of \(\mathrm{Mg}\) from \(\mathrm{MgCl}_{2}\) is (a) \(\overline{1}\) (b) 2 (c) \(0.5\) (d) 4

When 12,000 coulombs of electricity is passed through the electrolyte, \(3.0 \mathrm{~g}\) of a metal of atomic mass \(96.5 \mathrm{~g} / \mathrm{mol}\) is deposited. The electro-valency of the metal cation in the electrolyte is (a) \(+4\) (b) \(+3\) (c) \(+2\) (d) \(-4\)

How many electrons flow when a current of \(5 \mathrm{~A}\) is passed through a solution for \(200 \mathrm{~s}\) ? (a) \(6.022 \times 10^{23}\) (b) \(6.24 \times 10^{21}\) (c) \(6.024 \times 10^{21}\) (d) \(6.022 \times 10^{20}\)

The current of \(9.65\) A flowing for \(10 \mathrm{~min}\) deposits \(3.0 \mathrm{~g}\) of a metal. The equivalent weight of the metal is (a) 10 (b) 30 (c) 50 (d) \(96.5\)

The same current was passed successively through solution of zinc-ammonium sulphate and nickel-ammonium sulphate rendered alkaline with ammonia. The weights of zinc and nickel deposited in a certain time were found to be \(22.89 \mathrm{~g}\) and \(20.55 \mathrm{~g}\), respectively. Given that the chemical equivalent weight of zinc is \(32.7\), what is the chemical equivalent weight of nickel? (a) \(58.71\) (b) \(29.36\) (c) \(14.39\) (d) \(36.42\)

Which of the following solutions have highest resistance? (a) \(1 \mathrm{~N}-\mathrm{NaCl}\) (b) \(0.05 \mathrm{~N}-\mathrm{NaCl}\) (c) \(2 \mathrm{~N}-\mathrm{NaCl}\) (d) \(0.1 \mathrm{~N}-\mathrm{NaCl}\)

Variation of molar conductance of an electrolytic solution with temperature is that it (a) increases with increase of temperature (b) decreases with increase of temperature (c) first increases then decreases (d) is not affected by temperature

Which pure substance will not conduct electricity? (a) Molten \(\mathrm{NaCl}\) (b) Molten KOH

The correct order of molar conductance at infinite dilution of \(\mathrm{LiCl}, \mathrm{NaCl}\) and \(\mathrm{KCl}\) is (a) \(\mathrm{LiCl}>\mathrm{NaCl}>\mathrm{KCl}\) (b) \(\mathrm{KCl}>\mathrm{NaCl}>\mathrm{LiCl}\) (c) \(\mathrm{NaCl}>\mathrm{KCl}>\mathrm{LiCl}\) (d) \(\mathrm{LiCl}>\mathrm{KCl}>\mathrm{NaCl}\)

The molar conductance of a strong electrolyte at infinite dilution (a) tends to a finite value, which is above that at higher concentration (b) tends to a finite value, which is below that at higher concentration (c) tends to zero (d) tends to a finite value, which is equal

The best conductor of electricity is a \(0.1 \mathrm{M}\) solution of (a) Boric acid (b) Sulphuric acid (c) Acetic acid (d) Propanoic acid

The specific conductance of \(\mathrm{AgCl}\) solution in water was determined to be \(1.8 \times 10^{-6} \Omega^{-1} \mathrm{~cm}^{-1}\) at \(298 \mathrm{~K}\). The molar conductances at infinite dilution, of \(\mathrm{Ag}^{+}\) and \(\mathrm{Cl}^{-}\) are \(67.9\) and \(82.1 \Omega^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\), respectively. What is the solubility of AgCl in water? (a) \(1.2 \times 10^{-8} \mathrm{M}\) (b) \(1.44 \times 10^{-10} \mathrm{M}\) (c) \(1.2 \times 10^{-5} \mathrm{M}\) (d) \(1.44 \times 10^{-16} \mathrm{M}\)

Equivalence conductance at infinite dilution of \(\mathrm{NH}_{4} \mathrm{Cl}, \mathrm{NaOH}\) and \(\mathrm{NaCl}\) are 129.8, \(217.4\) and \(108.9 \Omega^{-1} \mathrm{~cm}^{2}\) \(\mathrm{mol}^{-1}\), respectively. If the equivalent conductance of \(0.01 \mathrm{~N}\) solution of \(\mathrm{NH}_{4} \mathrm{OH}\) is \(9.532 \Omega^{-1} \mathrm{~cm}^{2} \mathrm{~mol}^{-1}\), then the degree of dissociation of \(\mathrm{NH}_{4} \mathrm{OH}\) at this temperature is (a) \(0.04 \%\) (b) \(2.1 \%\) (c) \(4.0 \%\) (d) \(44.7 \%\)

The resistance of \(1 \mathrm{M}-\mathrm{CH}_{3} \mathrm{COOH}\) solution is \(250 \Omega\), when measured in a cell of cell constant \(125 \mathrm{~m}^{-1}\). The molar conductivity, in \(\Omega^{-1} \mathrm{~m}^{2} \mathrm{~mol}^{-1}\) is (a) \(5.0 \times 10^{-4}\) (b) 500 (c) \(2 \times 10^{-3}\) (d) 200

How does the electrical conductivity of \(20 \mathrm{ml}\) of \(0.2 \mathrm{M}-\mathrm{MgSO}_{4}\) change when \(0.5 \mathrm{M}-\mathrm{Ba}(\mathrm{OH})_{2}\) solution is gradually added in it, to excess? (a) decreases continuously (b) increases continuously (c) increases and then decreases (d) decreases am

The molar conductance of a \(0.01 \mathrm{M}\) solution of acetic acid was found to be \(16.30 \Omega^{-1} \mathrm{~cm}^{-1} \mathrm{~mol}^{-1}\) at \(25^{\circ} \mathrm{C}\). The ionic conductances of hydrogen and acetate ions at infinite dilution are \(349.8\) and \(40.9 \Omega^{-1}\) \(\mathrm{cm}^{-1} \mathrm{~mol}^{-1}\), respectively, at the same temperature. What percentage of acetic acid is dissociated at this concentration? (a) \(0.04172 \%\) (b) \(4.172 \%\) (c) \(41.72 \%\) (d) \(0.4172 \%\)

The distance between two electrodes of a cell is \(2.5 \mathrm{~cm}\) and area of each electrode is \(5 \mathrm{~cm}^{2}\). The cell constant is (a) \(0.5 \mathrm{~m}^{-1}\) (b) \(12.5 \mathrm{~cm}^{3}\) (c) \(2.0 \mathrm{~cm}\) (d) \(50 \mathrm{~m}^{-1}\)

In a conductivity cell, the two platinum electrodes, each of area \(10 \mathrm{~cm}^{2}\) are fixed \(1.5 \mathrm{~cm}\) apart. The cell contained \(0.05 \mathrm{~N}\) solution of a salt. If the two electrodes are just half dipped into the solution which has a resistance of \(50 \Omega\), the equivalent conductance of the salt solution, in \(\Omega^{-1}\) \(\mathrm{cm}^{2} \mathrm{eq}^{-1}\), is (a) 120 (b) 60 (c) 240 (d) 3000