Additional Questions - Chapter 9 - Electro Chemistry - 12th Chemistry Guide Samacheer Kalvi Solutions

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Additional Questions
1 Marks Questions And Answers
I. Choose the best answer and write it.
Question 1.
Which one of the following is an example of conductor?
(a) PVC
(b) Bakelite
(c) Aluminium
(d) Rubber
Answer:
(c) Aluminium
Question 2.
Which one of the following can act as an insulator?
(a) Bakelite
(b) Aluminium
(c) Copper
(d) NaCI Solution
Answer:
(a) Bakelite V
Question 3.
Which form of energy is converted to electrical energy in batteries?
(a) tidal energy
(b) Chemical energy
(c) mechanical energy
(d) atomic energy
Answer:
(b) Chemical energy
Question 4.
Electro chemical reactions are generally
(a) Reduction reactions
(b) oxidation reactions
(c) Redox reactions
(d) condensation reactions
Answer:
(c) Redox reactions

Question 5.
Consider the following statements.
Answer:
(i) Energy can neither be created nor be destroyed but one form of energy can be converted to another form
(ii) In batteries, electrical energy is converted to chemical energy.
(iii) Electrochemjcal reactions are redox reactions.
Which of the above statement is / are not correct?
(a) i \& ii only
(b) ii only
(c) i only
(d) iii only
Answer:
(b) ii only
Question 6.
Which one of the following represents Ohm's law?
(a) $\mathrm{V}=\mathrm{IR}$
(b) $\mathrm{R}=\frac{1}{V}$
(c) $\mathrm{I}=\frac{V}{R}$
(d) $\mathrm{R}=\mathrm{VI}$
Answer:
(a) $V=I R$
Question 7.
The unit of resistivity is
(a) $\Omega \mathrm{m}^{-1}$
(b) $\Omega \mathrm{m}$
(c) $\mathrm{m}^{-1} \mathrm{Ohm}^2$
(d) $\Omega^{-1} \mathrm{~m}^{-1}$
Answer:
(b) $\Omega \mathrm{m}$

Question 8.
When cell constant is unit, the resistance is known as
(a) specific resistance
(b) conductance
(c) specific conductance
(d) equivalent conductance
Answer:
(a) specific resistance
Question 9.
The unit of specific resistance is equal to ..........
(a) Ohm metre
(b) $\mathrm{Ohm}^{-1}$ metre
(c) $\mathrm{Ohm}^{-1}$ metre ${ }^{-1}$
(d) $\mathrm{Ohm}$
Answer:
(a) Ohm metre
Question 10.
Which is the SI unit of conductance?
(a) Siemen ${ }^{-1}$ (or) $\mathrm{S}^{-1}$
(b) Siemen (or) $\mathrm{S}$
(c) $\mathrm{Sm}^{-1}$
(d) $\mathrm{S}^{-1} \mathrm{~m}^{-1}$
Answer:
(b) Siemen (S)

Question 11.
Which one of the following represents specific conductance (kappa)?
(a) $\frac{I}{C} \cdot \frac{l}{a}$
(b) $\frac{I}{P} \cdot \frac{a}{I}$
(c) $\frac{1}{2} \cdot \frac{a}{l^2}$
(d) $\frac{I}{P} \cdot \frac{l}{a}$
Answer:
(d) $\frac{I}{P} \cdot \frac{l}{a}$
Question 12.
Which one is the unit of specific conductance?
(a) $\mathrm{Ohm} \mathrm{m}$
(b) $\mathrm{Ohm}^{-1} \mathrm{~m}$
(c) $\mathrm{Ohm} \mathrm{m}^{-1}$
(d) $\mathrm{Ohm}^{-1} \mathrm{~m}^{-1}$.
Answer:
(d) $\mathrm{Ohm}^{-1} \mathrm{~m}^{-1}$
Question 13.
Which one of the following formula represents equivalent conductance?
(a) $\frac{I}{P} \cdot \frac{l}{a}$
(b) $\frac{I}{P} \cdot \frac{A}{l}$
(c) $\mathrm{Cx} \frac{l}{a}$
(d) $\frac{\kappa \times 10^{-3}}{N}$
Answer:
(d) $\frac{\kappa \times 10^{-3}}{N}$
Question 14.
The unit of equivalent conductance is
(a) $\mathrm{Sm}^2 \mathrm{~g}$ equivalenr'
(b) $\mathrm{Sm}^{-1}$
(c) $\mathrm{Ohm}^{-1} \mathrm{~m}^{-1}$
(d) $\mathrm{Ohm} \mathrm{m}$
Answer:
(a) $\mathrm{Sm}^2$ g equivalent ${ }^{-1}$

Question 15.
Consider the following statements:
(i) Solvent of higher dielectric constant show very low conductance in solution.
(ii) Conductance is directly proportional to viscosity of the medium.
(iii) Molar conductance of a solution increases with increase in dilution. Which of the above statement is / are correct?
(a) (i) \& (ii)
(b) (ii) and (iii)
(c) (iii) only
(d) (i) only
Answer:
(c) (iii) only
Question 16.
Consider the following statements:
(i) If the temperature of the electrolytic solution increases, conductance decreases.
(ii) Conductivity increases with the decrease in viscosity.
(iii) Molar conductance of a solution decreases with increase in dilution.
Which of the above statement is / are not correct?
(a) (i) \& (iii)
(b) (i) and (ii)
(c) (iii) only
(d) (ii) only
Answer:
(a) (i) \& (iii)
Question 17.
Which one of the following is used to measure conductivity of ionic solutions?
(a) metre scale
(b) wheat stone bridge
(c) Dynamo
(d) Ammeter
Answer:
(b) wheat stone bridge

Question 18 .
Which of the following is used to calculate the conductivity of strong electrolytes?
(a) Kohlraush's law
(b) Henderson equation
(c) Debye-Huckel and Onsagar equation
(d) Ostwald's dilution law
Answer:
(c) Debye-Huckel and Onsagar equation
Question 19.
Which one of the following represents Debye-Huckel and Onsagar equation?
(a) $\left(\Lambda_{\mathrm{m}}^{\circ}\right)_{\mathrm{A}_{\mathrm{x}} \mathrm{B}_{\mathrm{y}}}=\mathrm{x}\left(\lambda_{\mathrm{m}}^0\right)_{\mathrm{A}^{\mathrm{y}}}+\mathrm{y}\left(\lambda_{\mathrm{m}}^0\right)_{\mathrm{B}^{x-}}$
(b) $\Lambda_{\mathrm{m}}=\Lambda_{\mathrm{m}^{-}}^{\circ}\left(\mathrm{A}+\mathrm{B} \Lambda_{\mathrm{m}}^{\circ}\right) \sqrt{\mathrm{C}}$
(c) $\mathrm{K}_{\mathrm{a}}=\frac{\alpha^2 \mathrm{C}}{1-\alpha}$
(d) $\Lambda_{\mathrm{m}}^{\circ}=\Lambda_{-}(\mathrm{A}+\mathrm{B}) \Lambda_{\mathrm{m}}^{\circ}-\mathrm{C}$
Answer:
(b) $\Lambda_{\mathrm{m}}=\Lambda_{\mathrm{m}^{-}}^{\circ}\left(\mathrm{A}+\mathrm{B} \Lambda_{\mathrm{m}}^{\circ}\right) \sqrt{\mathrm{C}}$

Question 20.
The value of $\mathrm{A}$ in Debye - Huckel and Onsagar equation is
(a) $\mathrm{A}=\frac{8.20 \times 10^5}{3 \sqrt{\mathrm{DT}}}$
(b) $\mathrm{A}=\frac{8.20 \times 10^{-5}}{\sqrt{\mathrm{DT}}}$
(c) $\mathrm{A}=\frac{82.4}{\sqrt{\mathrm{DT}} \eta}$
(d) $\mathrm{A}=\frac{82.4}{3 \sqrt{\mathrm{DT}}}$
Answer:
(c) $\mathrm{A}=\frac{82.4}{\sqrt{\mathrm{DT}} \eta}$
Question 21.
The value of B in Debye Huckel and onsagar equation is
(a) $\mathrm{B}=\frac{8.20 \times 10^5}{3 \sqrt{\mathrm{DT}}}$
(b) $\mathrm{B}=\frac{8.20 \times 10^{-5}}{\sqrt{\mathrm{DT}}}$
(c) $\mathrm{B}=\frac{82.4}{\sqrt{\mathrm{DT}} \eta}$
(d) $\mathrm{B}=\frac{82.4}{3 \sqrt{\mathrm{DT}}}$
Answer:
(a) $\mathrm{B}=\frac{8.20 \times 10^5}{3 \sqrt{\mathrm{DT}}}$

Question 22.
Kohlrausch's law is applied to calculate
(a) molar conductance at infinite dilution of a weak electrolyte
(b) degree of dissociation of weak electrolyte
(c) solubility of a sparingly soluble salt
(d) all the above
Answer:
(d) all the above
Question 23.
In which of the following interconversion of electrical energy into chemical energy and vice versa take place?
(a) electrochemical cell
(b) electric cell
(c) Dynamo
(d) $\mathrm{AC}$ generator
Answer:
(a) electrochemical cell
Question 24.
Consider the following statements:
(i) In Galvanic cell, chemical energy is'converted into electrical energy.
(ii) In electrolytic cell, electrical energy is converted into chemical energy.
(iii) In voltaic cell, electrical energy is converted into chemical energy.
Which of the above statement is / are not correct?
(a) (i) \& (ii)
(b) (iii) only
(c) (ii) only
(d) (i) only
Answer:
(b) (iii) only
Question 25.
In Galvanic cell, the Zinc metal strip placed gets
(a) Oxidised
(b) reduced
(c) hydrolysed
(d) condensed
Answer:
(a) Oxidised

Question 26.
Consider the following statements:
(i) In Galvanic cell, Zinc is oxidised to $\mathrm{Zn}^{2+}$ ions and $\mathrm{Cu}^{2+}$ ions are reduced to copper
(ii) In Galvanic cell, $\mathrm{Zn}^{2+}$ ions are reduced to $\mathrm{Zinc}$ and copper is oxidised to $\mathrm{Cu}^{2+}$ ions
(iii) In Galvanic cell, $\mathrm{Zn}$ and copper both get oxidised.
Which of the above statement is / are correct?
(a) (i) only
(b) (ii) & (iii)
(c) (ii) only
(d) (iii) only
Answer:
(a) (i) only
Question 27.
The salt bridge used in Daniel cell contains
(a) $\mathrm{Na}_2 \mathrm{SO}_4+\mathrm{NaCl}$
(b) Agar-Agar gel $+\mathrm{Na}_2 \mathrm{SO}_4$
(c) Silica gel $+\mathrm{CuSO}_4$
(d) $\mathrm{ZnSO}_4+\mathrm{CuSO}_4$
Answer:
(b) Agar-Agar gel $+\mathrm{Na}_2 \mathrm{SO}_4$
Question 28 .
Consider the following statements.
(i) In Daniel cell, when the switch (k) closes the circuit, the electrons flow from Zinc strip to copper strip.
(ii) In Daniel cell, when the switch (k) closes the circuit, the electrons flow from copper strip to Zinc strip
(iii) In Daniel cell, when the Switch (k) opens the circuit, the electrons flow from Zinc to copper.
Which of the above statement is / are correct?
(a) (i) only
(b) (ii) \& (iii)
(c) (ii) only
(d) (iii) only
Answer:
(a) (i) only

Question 29.
Which one of the following can act as an inert electrode?
(a) Graphite
(b) Copper
(c) Platinum
(d) either a (or) e
Answer:
(a) either a (or) $\mathrm{c}$
Question 30.
The SI unit of cell potential is
(a) Ampere
(b) $\mathrm{Ohm}$
(c) Volt
(d) $\mathrm{Ohm}^{-1}$
Answer:
(c) Volt
Question 31.
The emf of Daniel cell $\mathrm{Zn}_{(\mathrm{s})}+\mathrm{Zn}^{2+}{ }_{\mathrm{aq}(1 \mathrm{~m})} \| \mathrm{Cu}^{2+}{ }_{\mathrm{aq}(1 \mathrm{~m})} \mid \mathrm{Cu}_{(\mathrm{S})}$ iS equal to
(a) -1.107 Volts
(b) 1.107 Volts
(c) 3.4 Volt
(d) 7.6 Volt
Answer:
(b) 1.107 Volts
Question 32.
Which instrument is used to measure potential difference?
(a) Ammeter
(b) Voltmeter
(c) Wheat stone bridge
(d) metre bridge
Answer:
(b) Voltmeter

Question 33.
The value of $\mathrm{EMF}$ of standard hydrogen electrode at $25^{\circ} \mathrm{C}$ is
(a) maximum
(b) zero
(c) negative
(d) positive
Answer:
(b) zero
Question 34.
The electrode used in SHE is made of
(a) graphite
(b) copper
(c) platinum
(d) iron
Answer:
(c) Platinum
Question 35.
What is the charge of one electron?
(a) $1.602 \times 10^{19} \mathrm{C}$
(b) $1.6 \times 10^{-19} \mathrm{C}$
(c) $9645 \mathrm{C}$
(d) $96488 \mathrm{C}$
Answer:
(b) $1.6 \times 10^{-19} \mathrm{C}$
Question 36.
The maximum work that can be obtained from a galvanic cell is
(a) $+\mathrm{nFE}$
(b) $-\mathrm{nFE}$
(c) $2 \mathrm{~F}$
(d) $96500 \mathrm{~F}$
Answer:
(b) $-\mathrm{nFE}$
Question 37.
For all spontaneous cell reactions, the value of ?G should be
(a) constant
(b) zero
(c) negative
(d) positive
Answer:
(c) negative

Question 38.
The value of one Faraday is equal to
(a) $96400 \mathrm{C}$
(b) $96500 \mathrm{C}$
(c) $1.602 \times 10^{-19} \mathrm{C}$
(d) $1.602 \times 10^{19} \mathrm{C}$
Answer:
(b) $96500 \mathrm{C}$

Question 39.
The relationship between standard free energy change and equilibrium constant is expressed as .........
(a) $\Delta \mathrm{G}^{\circ}=-\mathrm{RTInk}_{\mathrm{eq}}$
(b) $\Delta \mathrm{G}=\mathrm{RT} \ln k_{\mathrm{eq}}$
(c) $\Delta \mathrm{G}^{\circ}=-\frac{1}{\mathrm{RT} \ln \mathrm{k}_{\mathrm{eq}}}$
(d) $\Delta \mathrm{G}=\mathrm{RT} \log _{\mathrm{eq}}$
Answer:
(a) $\Delta \mathrm{G}^{\circ}-\mathrm{RThilc}$
Question 40 .
Which equation relates the cell potential and the concentration of the species involved in an electro chemical reaction?
(a) Henderson equation
(b) Arrhenius equation
(c) Debye Huckel Onsagar equation
(d) Nemst equation
Answer:
(a) Nernst equation
Question 41.
Which one of the following is Nernst equation.
(a) $\mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}+\frac{0.0591}{\mathrm{n}} \log \frac{[\mathrm{C}]^1[\mathrm{D}]^{\mathrm{m}}}{[\mathrm{A}]^{\mathrm{x}}[\mathrm{B}]^{\mathrm{y}}}$
(b) $\mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}-\frac{0.0591}{\mathrm{n}} \log \frac{[\mathrm{A}]^{\mathrm{x}}[\mathrm{B}]^{\mathrm{y}}}{[\mathrm{C}]^{\mathrm{l}}[\mathrm{D}]^{\mathrm{m}}}$
(c) $\mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}-\frac{0.0591}{\mathrm{n}} \log \frac{[\mathrm{C}]^1[\mathrm{D}]^m}{[\mathrm{~A}]^{\mathrm{x}}[\mathrm{B}]^{\mathrm{y}}}$
(d) $\mathrm{E}_{\text {cell }}^{\circ}=\mathrm{E}_{\text {cell }}-\frac{0.0591}{\mathrm{n}} \log \frac{[\mathrm{A}]^{\mathrm{x}}[\mathrm{B}]^{\mathrm{y}}}{[\mathrm{C}]^1[\mathrm{D}]^{\mathrm{m}}}$
Answer:
(c) $\mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}-\frac{0.0591}{\mathrm{n}} \log \frac{[\mathrm{C}]^1[\mathrm{D}]^{\mathrm{m}}}{[\mathrm{A}]^{\mathrm{x}}[\mathrm{B}]^{\mathrm{y}}}$

Question 42.
Gibbs free energy can be related to cell emf as follows.
(a) $\Delta \mathrm{G}^{\circ}=-\mathrm{nFE}_{\text {cell }}$
(b) $\Delta \mathrm{G}^{\circ}=-\mathrm{nFE}^{\circ}$ cell
(c) $\Delta \mathrm{G}=\mathrm{nFE}_{\text {cell }}$
(d) $\Delta \mathrm{G}^{\circ}=\mathrm{nFE}^{\circ}$ cell
Answer:
(b) $\Delta \mathrm{G}^{\circ}=-\mathrm{nFE}^{\circ}$ cell
Question 43.
Which one of the following represents Faraday's first law?
(a) $m=\mathrm{ZIt}$
(b) $\mathrm{m}=\frac{Z}{I t}$
(c) $\mathrm{m}=\frac{I t}{Z}$
(d) $\mathrm{Z}=\mathrm{mIt}$
Answer:
(a) $\mathrm{m}=$ ZIt
Question 44 .
When 1 coulomb of electric current is passed the amount of substance deposited or liberated is known as
(a) equivalent mass
(b) electro chemical equivalent
(c) molar mass
(d) 1 Faraday
Answer:
(b) electro chemical equivalent
Question 45.
The value of electro chemical equivalent is equal to
(a) $\frac{96500}{\text { Equivalent mass }}$
(b) $\frac{96500}{\text { Molar mass }}$
(c) $\frac{\text { Molar mass }}{96500}$
(d) $\frac{\text { Equivalent mass }}{96500}$
Answer:
(d) $\frac{\text { Equivalent mass }}{96500}$

Question 46.
The mathematical expression of Faraday's second law is
(a) $\mathrm{m}=\mathrm{ZIt}$
(b) $\frac{m_1}{E_1}=\frac{m_2}{E_2}=\frac{m_3}{E_3}$
(c) $\frac{m_1}{Z_1}=\frac{m_2}{Z_2}=\frac{m_3}{Z_3}$
(d) $Z=\frac{m}{I t}$
Answer:
(c) $\frac{m_1}{Z_1}=\frac{m_2}{Z_2}=\frac{m_3}{Z_3}$
Question 47.
Which one of the following is used in cell phone, dry cell in flashlight?
(a) $\mathrm{Zn}-\mathrm{Cu}$ battery
(b) $\mathrm{Li}$ - ion battery
(c) $\mathrm{Ag}-\mathrm{Cu}$ battery
(d) $\mathrm{Na}, \mathrm{NaCI}$ battery
Answer:
(b) $\mathrm{Li}$ - ion battery
Question 48.
The primary batteries are
(a) rechargeable
(b) non - rechargeable
(c) reversible
(d) renewable
Answer:
(b) non - rechargeable
Question 49.
Consider the following statements.
(i) The secondary batteries are rechargeable
(ii) Primary batteries are non - rechargeable
(iii) Batteries are used as a source of $\mathrm{AC}$ current at a constant voltage.
Which of the above statement is I are not correct?
(a) (i) \& (ii)
(b) (iii) only
(c) (i) only
(d) (ii) only
Answer:
(b) (iii) only

Question 50 .
The anode and cathode used in Leclanche cell are respectively.
(a) Zinc, Graphite rod with $\mathrm{MnO}_2$
(b) Graphite rod in $\mathrm{MnO}_2$ and Zinc container
(c) $\mathrm{Zn}$ container and copper rod
(d) Copper container and Zinc rod
Answer:
(a) Zinc, Graphite rod with $\mathrm{MnO}_2$
Question 51.
Which electrolyte is used in Leclanche cell?
(a) $\mathrm{ZnSO}_4+\mathrm{CuSO}_4$
(b) $\mathrm{NH}_4 \mathrm{CI}+\mathrm{ZnCl}_2$
(c) $\mathrm{NaCI}+\mathrm{CuSO}_4$
(d) $\mathrm{MnSO}_4+\mathrm{MnO}_2$
Answer:
(b) $\mathrm{NH}_4 \mathrm{Cl}+\mathrm{ZnCl}_2$
Question 52.
Which one of the following is used as cathode in Mercury button cell?
(a) Zinc
(b) Copper
(c) Zinc amalgamated with mercury
(d) $\mathrm{HgO}$ mixed with graphite
Answer:
(c) Zinc amalgamated with mercury
Question 53.
Which one of the following is used as anode in Mercury button cell?
(a) $\mathrm{HgO}$ mixed with graphite
(b) Zinc amalgamated with mercury
(c) Copper amalgamated with Mercury
(d) $\mathrm{HgO}$ mixed with Copper
Answer:
(a) $\mathrm{HgO}$ mixed with graphite.

Question 54.
The value of cell emf of Mercury button cell is
(a) $1.35 \mathrm{~V}$
(b) $-076 \mathrm{~V}$
(c) $0.34 \mathrm{~V}$
(d) $100 \mathrm{~V}$
Answer:
(a) $1.35 \mathrm{~V}$
Which one of the following is used in pacemakers, cameras and electronic watches?
(a) Li-ion battery
(b) Leclanche cell
(c) Galvanic cell
(d) Mercurry button cell
Answer:
(d) Mercury button cell
Question 56.
The electrolyte used in Mercury button cell is
(a) Paste of $\mathrm{kOH}$ and $\mathrm{ZnO}$
(b) $\mathrm{CuSO}_4+\mathrm{ZnSO}_4$
(c) $\mathrm{NaCl}+\mathrm{MgCl}_2$
(d) $\mathrm{NH}_4 \mathrm{CI}+\mathrm{ZnCl}_2$
Answer:
(a) Paste of $\mathrm{kOH}$ and $\mathrm{ZnO}$
Question 57.
Which of the following is an example of secondary batteries?
(a) Mercury button cell
(b) Leclanche cell
(c) Lead storage battery
(d) Daniel cell
Answer:
(c) Lead storage battery

Question 58.
Which of the following act as cathode and anode in Lead storage battery?
(a) Lead plate bearing $\mathrm{PbO}_2$, spongy Lead
(b) Spongy lead, lead plate bearing $\mathrm{PbO}_2$
(c) Lead Copper
(d) Mercury oxide, $\mathrm{PbO}$
Answer:
(a) Lead plate bearing $\mathrm{PbO}_2$, Spongy lead
Question 59.
Which one of the following is used as an electrolyte Lead storage battery?
(a) $\mathrm{PbSO}_4$
(b) $\mathrm{H}_2 \mathrm{SO}_4$
(c) $\mathrm{CuSO}_4$
(d) $\mathrm{HNO}_3$
Answer:
(b) $\mathrm{H}_2 \mathrm{SO}_4$
Question 60 .
The emf of lead storage battery is
(a) $+1.1 \mathrm{~V}$
(b) $2.4 \mathrm{~V}$
(c) $2 \mathrm{~V}$
(d) $11.2 \mathrm{~V}$
Answer:
(c) $2 \mathrm{~V}$
Question 61.
The Lead storage battery is used in
(a) pacemakers
(b) automobiles
(c) electronic watches
(d) flash light
Answer:
(b) automobiles
Question 62.
Which one of the following is used in automobiles, trains and in inverters?
(a) Lithium ion battery
(b) Mercurry button cell
(c) Lead storage battery
(d) Leclanche cell
Answer:
(c) Lead storage battery

Question 63.
Which one of the following is used as an anode in Lithium ion battery?
(a) Porous graphite
(b) Lithium
(c) $\mathrm{CoO}_2$
(d) Copper
Answer:
(a) Porous graphite
Question 64 .
which one of the following is used as cathode in Lithium ion battery?
(a) Porous graphite
(b) Lithium
(c) $\mathrm{CoO}_2$
(d) Chromium
Answer:
(c) $\mathrm{CoO}_2$
Question 65 .
Which one of the following is used in cellular phones, Laptop computers and in digital camera?
(a) Mercury button cell
(b) Lithium - ion battery
(c) $\mathrm{H}_2 \mathrm{O}_2$ fuel cell
(d) Leclanche cell
Answer:
(b) Lithium - ion battery
Question 66.
Which one of the following is used as an electrolyte in $\mathrm{H}_2 \mathrm{O}_2$ fuel cell?
(a) Aqueous $\mathrm{CuSO}_4$
(b) Aqueous $\mathrm{CoO}_2$
(c) Aqueous $\mathrm{KOH}$
(d) $\mathrm{NH}_4 \mathrm{CI}+\mathrm{ZnCI}_2$
Answer:
(c) Aqueous $\mathrm{KOH}$

Question 67.
Which one of the following is an example for electrochemical process?
(a) Chrome plating
(b) Rusting of iron
(c) Galvanisation
(d) All the above
Answer:
(a) All the above
Question 68 .
The formula of rust is
(a) $\mathrm{Fe}_2 \mathrm{O}_3$
(b) $\mathrm{Fe}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}$
(c) $\mathrm{FeO}$
(d) $\mathrm{FeO} \cdot \mathrm{xH}_2 \mathrm{O}$
Answer:
(b) $\mathrm{Fe}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}$
Question 69.
Which one of the following is / are very important for rusting'?
(a) Oxygen
(b) Water
(c) Both a \& b
(d) $\mathrm{H}_2 \mathrm{O}$
Answer:
(c) Both a \& b
Question 70.
The electro plating of Zinc over a metal is called
(a) Electrolysis
(b) Redox reaction
(c) Galvanisation
(d) Passivation
Answer:
(c) Galvanisation

Question 71.
Consider the following statements.
(i) The standard reduction potential $\left(\mathrm{E}^{\circ}\right)$ is a measure of oxidising tendency of the species.
(ii) The standard oxidation potential $\left(\mathrm{E}^{\circ}\right)$ is a measure of oxidising tendency of the species.
(iii) The standard oxidation potential $\left(\mathrm{E}^{\circ}\right)$ is a measure of redox tendency of the species.
Which of the above statement is / are not correct?
(a) (i) only
(b) (ii) only
(c) (ii) \& (iii)
(d) (iii) only
Answer:
(c) (ii) & (iii)
Question 72.
On the basis of the electrochemical theory of aqueous corrosion, the reaction occuring at the cathode is
(a) $\mathrm{O}_{2(\mathrm{~g})}+4 \mathrm{H}_{(\mathrm{aq})}^{+}+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}$
(b) $\mathrm{Fe}_{(\mathrm{s})} \rightarrow \mathrm{Fe}_{(\mathrm{aq})}^{2+}+2 \mathrm{e}^{-}$
(c) $\mathrm{Fe}_{(\mathrm{aq})}^{2+} \rightarrow \mathrm{Fe}_{(\mathrm{aq})}^{3+}+\mathrm{e}^{-}$
(d) $\mathrm{H}_{2(\mathrm{~g})}+2 \mathrm{OH}_{(\mathrm{aq})}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}+2 \mathrm{e}^{-}$
Answer:
(a) $\mathrm{O}_{2(\mathrm{~g})}+4 \mathrm{H}_{(\mathrm{aq}) 2+}^{+}+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}$
Hint:
$
\begin{aligned}
& 2 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \\
& 2 \mathrm{H}^{+}+\frac{1}{2} \mathrm{O}_2 \rightarrow \mathrm{H}_2 \mathrm{O} \\
& 2 \mathrm{H}^{+}+\frac{1}{2} \mathrm{O}_2+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_2 \mathrm{O}
\end{aligned}
$
Balancing the above equation
$
4 \mathrm{H}_{(\mathrm{aq})}^{+}+\mathrm{O}_2+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}
$

Question 73.
The standard reduction potential for the half reactions are as
$
\begin{aligned}
& \mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-} \mathrm{E}^{\circ}=+0.76 \mathrm{~V} \\
& \mathrm{Fe} \rightarrow \mathrm{Fe}^{2+}+2 \mathrm{e}^{-\mathrm{E}^{\circ}}=+041 \mathrm{~V}
\end{aligned}
$
So for cell reaction $\mathrm{F}^{2+}+\mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+\mathrm{Fe}$ is
(a) $-0.35 \mathrm{~V}$
(b) $+0.35 \mathrm{~V}$
(c) $+1.17 \mathrm{~V}$
(d) $-1.117 \mathrm{~V}$
Answer:
(b) $+0.35 \mathrm{~V}$
Hint:
In the reaction $\mathrm{F}^{2+}+\mathrm{Zn}^{\circ} \rightarrow \mathrm{Zn}^{2+}+\mathrm{Fe}^{\circ}$
emf $=\mathrm{E}_{\text {cathode }}-\mathrm{E}_{\text {anode }}$
$=-0.41-(-0.76)$
$=-0.41+0.76$
$\mathrm{emf}=+0.35 \mathrm{~V}$
Question 74.
The standard emf for the given cell reaction $\mathrm{Zn}+\mathrm{Cu}^{2+} \rightarrow \mathrm{Cu}+\mathrm{Zn}^{2+}$ is $1.10 \mathrm{~V}$ at $25^{\circ} \mathrm{C}$. The emf for the cell reaction when $0.1 \mathrm{M} \mathrm{Cu}^{2+}$ and $0.1 \mathrm{M} \mathrm{Zn}^{2+}$ solutions are used at $25^{\circ} \mathrm{C}$ is
(a) $1.10 \mathrm{~V}$
(b) $0.110 \mathrm{~V}$
(c) $-1.10 \mathrm{~V}$
(d) $-110 \mathrm{~V}$
Answer:
(a) $1.10 \mathrm{~V}$
Hint:
$
\begin{aligned}
& \mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}-\frac{0.0592}{2} \log \frac{\left(\mathrm{Zn}^{2+}\right)}{\left(\mathrm{Cu}^{2+}\right)} \\
& =1.10-\frac{0.0592}{2} \log \frac{0.1}{0.1} \\
& =1.10-\frac{0.0592}{2} \log 1 \\
& =1.10-\frac{0.0592}{2} \times 0 \\
& =1.10 \mathrm{~V}
\end{aligned}
$

Question 75.
Which amount of chlorine gas liberated at anode, if 1 ampere current is passed for 30 minutes from $\mathrm{NaCI}$ solution?
(a) 0.66 moles
(b) 0.33 moles
(c) $0.66 \mathrm{~g}$
(d) $0.33 \mathrm{~g}$
Answer:
(c) $0.66 \mathrm{~g}$
Hint:
$
\begin{aligned}
& 2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_2+2 \mathrm{e}^{-} \\
& \mathrm{Q}=\mathrm{It} .
\end{aligned}
$
Amount of current passed $=1 \times 30 \times 60=1800 \mathrm{C}$
The amount of $\mathrm{Cl}_2$ liberated by passing 1800 coulomb of electric charge
$
\begin{aligned}
& =\frac{1 \times 1800 \times 71}{2 \times 96500} \\
& =0.66 \mathrm{~g}
\end{aligned}
$
Question 76.
When Zinc piece is kept in $\mathrm{CuSO}_4$ solution the copper gets precipitated due to standard potential of Zinc is
(a) $>$ copper
(b) < copper
(c) $>$ Sulphate
(d) $<$ Sulphate
Answer:
(b) < copper
Hint:
Standard potential of zinc $<$ copper.
Question 77.
Which equation shows the relation between electrode potential (E) standard electrode potential $\left(\mathrm{E}^{\circ}\right)$ and concentration of ions in solution is
(a) Kohlrausch's equation
(b) Nernst equation
(c) Ohm's equation
(d) Faraday's equation
Answer:
(b) Nernst equation

Question 81.
The correct order of chemical reactivity with water according to electrochemical series
(a) $\mathrm{K}>\mathrm{Mg}>\mathrm{Zn}>\mathrm{Cu}$
(b) $\mathrm{Mg}>\mathrm{Zn}>\mathrm{Cu}>\mathrm{K}$
(c) $\mathrm{K}>\mathrm{Zn}>\mathrm{Mg}>\mathrm{Cu}$
(d) $\mathrm{Cu}>\mathrm{Zn}>\mathrm{Mg}>\mathrm{K}$
Answer:
(a) $\mathrm{K}>\mathrm{Mg}>\mathrm{Zn}>\mathrm{Cu}$
Hint:
The standard reduction potential of $\mathrm{K}^{+}, \mathrm{Mg}^{2+}, \mathrm{Zn}^{2+}, \mathrm{Cu}^{2+}$ increases in this order.
Question 82.
For a spontaneous reaction, the $\Delta \mathrm{G}$, the equilibrium constant $(\mathrm{K})$ and $\mathrm{E}^{\circ}$ cell will be respectively
(a) $\mathrm{ve},>1,+$ ve
(b) + ve $,>1,-$ ve
(c) - ve, $<1,-$ ve (d) $-\mathrm{ve},>1,-$ ve
Answer:
(a) $-\mathrm{ve},>1,+\mathrm{ve}$.
Question 83.
$\mathrm{E}^{\circ}$ values of $\mathrm{mg}^{2+} / \mathrm{mg}$ is $-2.37 \mathrm{~V}, \mathrm{Zn}^{2+} / \mathrm{Zn}$ is $-0.76 \mathrm{~V}$, and $\mathrm{Fe}^{2+} / \mathrm{Fe}$ is $-0.44 \mathrm{~V}$. Which of the following statement is correct?
(a) $\mathrm{Zn}$ will reduce $\mathrm{Fe}^{2+}$
(b) $\mathrm{Zn}$ will reduce $\mathrm{mg}^{2+}$
(c) mg oxidises $\mathrm{Fe}$
(d) Zn oxidises $\mathrm{Fe}$
Answer:
(a) $\mathrm{Zn}$ will reduce $\mathrm{Fe}^{2+}$
Hint:
$\mathrm{E}^0 \mathrm{Zn}^{2+} / \mathrm{Zn}^{<\mathrm{E}^0 \mathrm{Fe}^{2+} / \mathrm{Fe}}$ So $\mathrm{Zn}$ will reduce $\mathrm{Fe}^{2+}$. Zinc cannot reduce $\mathrm{Mg}^{2+}$ because
$\mathbf{E}_{\mathbf{Z n}^{2+} / \mathbf{z n}}^{\circ}>\mathbf{E}_{\mathrm{Mg}^{2+} / \mathrm{Mg}}^{\circ}$ On similar reason $\mathrm{mg}$ and $\mathrm{Zn}$ cannot oxidise $\mathrm{Fe}$.
Question 84 .
In which cell, the free energy of a chemical reaction is directly converted into electricity?
(a) Leclanche cell
(b) Fuel cell
(c) Lead storage battery
(d) Lithium ion battery

Answer:
(b) Fuel cell
Question 85.
Which of the following has the highest electrode potential?
(a) $\mathrm{Li}$
(b) $\mathrm{Cu}$
(c) Au
(d) Al
Answer:
(c) Au
Question 86.
Consider the following statements.
(i) A salt bridge is used to eliminate liquid junction potential
(ii) The Gibbs free energy change $\Delta \mathrm{G}$ is related with electro motive force (E) as $\Delta \mathrm{G}=-\mathrm{nFE}$.
(iii) Nernst equation for a single electrode potential is $\mathrm{E}=\mathrm{E}^{\circ}-\frac{R T}{n F}$ In $a_m n^4$
(iv) The efficiency of a hydrogen oxygen fuel cell is $23 \%$.
Which of the above statement is / are not correct?
(a) (i) \& (ii)
(b) (ii) \& (iii)
(c) (iv) only
(d) (i) only
Answer:
(c) (iv) only
Question 87.
The specific conductance of $0.1 \mathrm{~N} \mathrm{KCl}$ solution at $23^{\circ} \mathrm{C}$ is $0.012 \mathrm{Ohm}^{-1} \mathrm{~cm}^{-1}$. The resistance of the cell containing the solution at the same temperature was found to be $55 \mathrm{Ohm}$. The cell constant will be
(a) $0.142 \mathrm{~cm}^{-1}$
(b) $0.66 \mathrm{~cm}^{-1}$
(c) $0.918 \mathrm{~cm}^{-1}$
(d) $1.12 \mathrm{~cm}^{-1}$
Answer:
(c) $0.66 \mathrm{~cm}^{-1}$
Hint:
$\mathrm{k} \times \frac{1}{R} \mathrm{x}$ cell constant
Cell constant $=\mathrm{k} \times \mathrm{R}$
$=0.012 \times 55$
$=0.66 \mathrm{~cm}^{-1}$

Question 88 .
Which of the following reaction is used to make a fuel cell?
(a) $\mathrm{Cd}_{(\mathrm{s})}+2 \mathrm{Ni}(\mathrm{OH})_{3(\mathrm{~s})} \rightarrow \mathrm{CdO}_{(\mathrm{s})}+2 \mathrm{Ni}(\mathrm{OH})+\mathrm{H}_2 \mathrm{O}_{(1)}$
(b) $\mathrm{Pb}_{(\mathrm{s})}+\mathrm{PbO}_{2(\mathrm{~s})}+2 \mathrm{H}_2 \mathrm{SO}_{4(\mathrm{aq})} \rightarrow 2 \mathrm{PbSO}_{4(\mathrm{~s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)}$
(c) $2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{O}_{(\mathrm{s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)}$
(d) $2 \mathrm{Fe}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{~g})}+4 \mathrm{H}_{(\mathrm{ag})}^{+}+2 \mathrm{Fe}_{4(\mathrm{~s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)}$
Answer:
(c) $2 \mathrm{H}_{2(\mathrm{~g})}+\mathrm{O}_{(\mathrm{s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)}$
When lead storage battery is charged
(a) $\mathrm{PbO}_2$ is dissolved
(b) $\mathrm{PbSO}_4$ is deposited on lead electrode
(c) $\mathrm{PbSO}_4$ is deposited on lead electrode
Question 89.
Which colourless gas evolves when $\mathrm{NH}_4 \mathrm{CI}$ reacts with Zinc in a dry cell battery?
(a) $\mathrm{NH}_3$
(b) $\mathrm{N}_2$
(c) $\mathrm{H}_2$
(d) $\mathrm{Cl}_2$
Answer:
(c) $\mathrm{H}_2$
Hint: $2 \mathrm{NH}_4 \mathrm{Cl}+\mathrm{Zn} \rightarrow 2 \mathrm{NH}_3+\mathrm{ZnCl}_2+\mathrm{H}_2 \uparrow$
Question 91.
A cell from the following which converts electrical energy into chemical energy?
(b) Electro chemical cell
(d) Lithium - ion battery
(a) dry cell
(c) Electrolytic cell

Question 92.
When 9.65 Coulombs of electricity is passed through a solution of silver nitrate (Atomic weight of $\mathrm{Ag}=$ $107.85 \mathrm{~g}$ ), the amount of silver deposited is
(a) $10.8 \mathrm{mg}$
(b) $5.4 \mathrm{mg}$
(c) $16.2 \mathrm{mg}$
(d) $21.2 \mathrm{mg}$
Answer:
(a) $10.8 \mathrm{mg}$
Hint:
$
\begin{aligned}
& \mathrm{W}_{\mathrm{Ag}}=\frac{E_{A g} \times Q}{96500}=\frac{108 \times 9.65}{96500} \\
& =1.08 \times 10^{-2}
\end{aligned}
$

Question 93.
What weight of copper will be deposited by passing 2 Faraday's of electricity through a cupric salt (Atomic weight of $\mathrm{Cu}=63.5$ )
(a) $2.0 \mathrm{~g}$
(b) $3.175 \mathrm{~g}$
(c) $63.5 \mathrm{~g}$
(d) $127.0 \mathrm{~g}$
Answer:
(c) $63.5 \mathrm{~g}$
Hint:
$\mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}$
2 Faraday's will deposit $1 \mathrm{~g}$ atom of $\mathrm{Cu}=63.5 \mathrm{~g}$
Question 94.
In electrolysis of a fused salt, the weight of the deposit on an electrode will not depend on ....
(a) temperature of the bath
(b) current intensity
(c) electro chemical equivalent of ions
(d) time for electrolysis.
Answer:
(a) temperature of the bath
Question 95.
The mass deposited at an electrode is directly proportional to
(a) atomic weight
(b) equivalent weight
(c) molecular weight
(d) atomic number
Answer:
(b) equivalent weight
Question 96.
Which solution will show the highest resistance during the passage of current?
(a) $0.05 \mathrm{~N} \mathrm{NaCl}$
(b) $2 \mathrm{~N} \mathrm{NaCI}$
(c) $0.1 \mathrm{~N} \mathrm{NaCI}$
(d) $1 \mathrm{~N} \mathrm{NaCI}$
Answer:
(b) $2 \mathrm{~N} \mathrm{NaCl}$

Question 97.
In a galvanic cell, the electrons flow from
(a) anode to cathode through the solution
(b) cathode to anode through the solution
(c) anode to cathode through the external circuit
(d) cathode to anode through the external circuit
Answer:
(c) anode to cathode through the external circuit
Question 98.
Rusting of iron is catalysed by which of the following?
(a) $\mathrm{Fe}$
(b) $\mathrm{O}_2$
(c) $\mathrm{Zn}$
(d) $\mathrm{H}$
Answer:
(d) $\mathrm{H}$
Question 99.
The conductivity of strong electrolyte is
(a) increase on dilution slightly
(b) decrease on dilution
(c) does not change with dilution
(d) depend upon density of electrolyte itself
Answer:
(a) increase on dilutions lightly
Question 100 .
Which one is not a conductor of electricity?
(a) $\mathrm{NaCl}_{\text {(aqueous) }}$
(b) $\mathrm{NaCl}_{\text {(solid) }}$
(c) $\mathrm{NaCl}_{(\text {molten) }}$
(d) $\mathrm{Ag}_{\text {(metal) }}$
Answer:
(b) $\mathrm{NaCl}_{(\text {solid) }}$
Hint:
In solid state, $\mathrm{NaCl}$ does not dissociate into ions so it does not conduct electricity.

Question 101.
The molar conductivity is maximum for the solution of concentration
(a) $0.001 \mathrm{~m}$
(b) $0.005 \mathrm{~m}$
(c) $0.002 \mathrm{~m}$
(d) $0.004 \mathrm{~m}$
Answer:
(a) $0.001 \mathrm{~m}$
Hint:
molar conductance $\alpha \frac{1}{\text { molarity }}$
Question 102.
Resistance of $0.2 \mathrm{~m}$ solution of an electrolyte is $50 \mathrm{Ohm}^{-1}$. The specific conductance of the solution is 1.3 $\mathrm{Sm}^{-1}$. If resistance of $0.4 \mathrm{~m}$ solution of the same electrolyte is $260 \mathrm{Ohm}^{-1}$, its molar conductivity is
(a) $62.5 \mathrm{Sm}^2 \mathrm{~mol}^{-1}$
(b) $6250 \mathrm{Sm}^2 \mathrm{~mol}^{-1}$
(c) $6.25 \times 10^{-4} \mathrm{Sm}^2 \mathrm{~mol}^{-1}$
(d) $625 \times 10^{-4} \mathrm{Sm}^2 \mathrm{~mol}^{-1}$
Answer:
(c) $6.25 \times 10^{-4} \mathrm{Sm}^2 \mathrm{~mol}^{-1}$
Question 103.
Saturated solution of $\mathrm{KCI}$ (or) $\mathrm{Na}_2 \mathrm{SO}_4$ is used to make salt bridge because
(a) velocity of $\mathrm{K}^{+}$is greater than that of $\mathrm{Cl}^{-}$
(b) velocity of $\mathrm{Cl}^{-}$is greater than that of $\mathrm{K}^{+}$
(c) velocity of both $\mathrm{K}^{+}$and $\mathrm{Cl}^{-1}$ are nearly the same
(d) $\mathrm{KCI}$ is highly soluble in water.
Answer:
(c) velocity of both $\mathrm{K}^{+}$and $\mathrm{Cl}^{-}$are nearly the same

Question 104.
Which of the following electrolytic solutions has the least specific conductance?
(a) $0.02 \mathrm{~N}$
(b) $0.2 \mathrm{~N}$
(c) $2 \mathrm{~N}$
(d) $0.002 \mathrm{~N}$
Answer:
(d) $0.002 \mathrm{~N}$
Question 105.
An increase in equivalent conductance of a strong electrolyte with dilution is mainly due to
(a) increase in both the number of ions and ionic mobility of ions
(b) increase in number of ions
(c) increase in ionic mobility of ions
(d) $100 \%$ ionization of electrolyte at normal dilution
Answer:
(c) increase in ionic mobility of ions
Question 106.
$\mathrm{Li}$ occupies higher position in the electrochcmical series of metals as compared to $\mathrm{Cu}$, since
(a) the standard reduction potential of $\mathrm{Li}^{+} / \mathrm{Li}$ is lower than that of $\mathrm{Cu}^{2+} / \mathrm{Cu}$
(b) the standard reduction potential of $\mathrm{Cu}^{2+} / \mathrm{Cu}$ is lower than that of $\mathrm{Li}^{+} / \mathrm{Li}$
(c) the standard oxidation potential of $\mathrm{Li} / \mathrm{Li}^{+}$is lower than that $\mathrm{Cu} / \mathrm{Cu}^{2+}$
(d) $\mathrm{Li}$ is smaller in size as compared to $\mathrm{Cu}$.
Answer:
(a) the standard reduction potential of $\mathrm{Li}^{+} / \mathrm{Li}$ is lower than that of $\mathrm{Cu}^{2+} / \mathrm{Cu}$
Question 107.
The one which decreases with dilution is
(a) conductance
(b) specific conductance
(c) equivalent conductance
(d) molar conductance
Answer:
(b) specific conductance
Question 108.
Corrosion of iron is essentially an electrochemical phenomenon where the cell reactions are
(a) $\mathrm{Fe}$ is oxidised to $\mathrm{Fe}^{2+}$ and dissolved oxygen in water is reduced to $\mathrm{OH}^{-}$
(b) $\mathrm{Fe}$ is oxidised to $\mathrm{Fe}^{2+}$ and $\mathrm{H}_2 \mathrm{O}$ is reduced to $\mathrm{O}_2{ }^{2-}$
(c) $\mathrm{Fe}$ is oxidised to $\mathrm{Fe}^{2+}$ and $\mathrm{H}_2 \mathrm{O}$ is reduced to $\mathrm{O}_2^{-}$
(d) $\mathrm{Fe}$ is oxidised to $\mathrm{Fe}^{2+}$ and $\mathrm{H}_2 \mathrm{O}$ is reduced to $\mathrm{O}_2$
Answer:
(a) $\mathrm{Fe}$ is oxidised to $\mathrm{Fe}^{2+}$ and dissolved oxygen in water is reduced to $\mathrm{OH}^{-2}$
Question 109.
A button cell used in watches functions as following.
$
\mathrm{Zn}_{(\mathrm{s})}+\mathrm{Ag}_2 \mathrm{O}_{(\mathrm{s})}+\mathrm{H}_2 \mathrm{O}_{(1)} \rightarrow 2 \mathrm{Ag}_{(\mathrm{s})}+\mathrm{Zn}^{2+}{ }_{(\mathrm{aq})}+2 \mathrm{OHsup}>_{-(\mathrm{aq})} \text {. }
$
If half cell potentials are $\mathrm{Zn}^{2+}{ }_{(\mathrm{aq})}+2 \mathrm{e}^{-} \rightarrow \mathrm{Zn}_{(\mathrm{s})}$
$
\begin{aligned}
& \mathrm{E}^{\circ}=-\mathrm{O} .76 \mathrm{~V} \\
& \mathrm{Ag}_2 \mathrm{O}_{(\mathrm{s})}+\mathrm{H}_2 \mathrm{O}_{(1)}+2 \mathrm{e}^{-} 2 \mathrm{Ag}_{(\mathrm{s})}+2 \mathrm{OH}^{-}{ }_{(\mathrm{aq})} \mathrm{E}^0=0.34 \mathrm{~V}
\end{aligned}
$
The cell potential will be .........
(a) $1.10 \mathrm{~V}$
(b) $0.42 \mathrm{~V}$
(c) $0.84 \mathrm{~V}$
(d) $1.34 \mathrm{~V}$
Answer:
(a) $1.10 \mathrm{~V}$
Hint:
Cell potential $=\mathrm{E}_{\text {cathode }}-\mathrm{E}_{\text {anode }}$
$=0.34-(-0.76)$
$=0.34+0.76$
$=1.10 \mathrm{~V}$
Question 110.
Among the following cells Leclanche cell
(I) Nickel - cadmium cell
(II) Lead storage battery
(III) and Mercury Cell
(IV) primary cells are
(a) I & II
(b) I & III
(c) II & III
(d) I & IV
Answer:
(d) I \& IV

II. Fill in the blanks.
1. .............................. is defined as the resistance of an electrolyte confined between two electrodes having unit cross sectional area and separated by a unit distance
2. The reciprocal of the specific resistance is called the and represented by the symbol ..............
3. The SI unit of specific conductance is ........
4. The relation between equivalent conductance and the specific conductance is given as ................
5. Conductivity increases with the .................... in viscosity.
6. $\mathrm{A}^{\circ} \mathrm{m}$ values of the weak electrolytes can be determined using..................... 
7. .................... is a device in which a spontaneous chemical reaction generates an electric current.
8. ....... is a device that converts electrical energy into chemical energy.
9. The salt bridge contains a agar-agar gel mixed with an inert electrolyte such as ...................
10. The SI unit of cell potential is ...............
11. The reference electrode SHE has emf of exactly volt .................
12. The value of charge of one electron is equal to ................
13. For a spontaneous cell reaction, the should be ....................
14. ...................... is a process in which electrical energy is used to cause a non-spontaneous chemical reaction.
15. The negative $E^{\circ}$ values shows that the reactions are.............................
16. ....... is defined as the amount of a substance deposited or liberated at the electrode by a charge of 1 Coulomb.
17 ................... batteries are used in cell phones.
18. ..................... cell is used in pacemakers, electronic watches and cameras.
19. ........ battery is used in automobiles.
20. Rusting of iron is an ....................... process.

Answer:
1. Specific resistance (or) Resistivity
2. Specific conductance, Kappa(k)
3. $\mathrm{Sm}^{-1}$
4. $\Lambda=\frac{\kappa \times 10^{-3}}{N}$
5. decrease
6. Kohlraush's law
7. Galvanic (or) Voltaic cell
8. Electrolytic cell
9. $\mathrm{KCl}$ (or) $\mathrm{Na}_2 \mathrm{SO}_4$
10. Volt (V)
11. zero
12. $1.6 \times 10^{-19} \mathrm{C}$
13. negative
14. Electrolysis
15. non - spontaneous
16. electro chemical equivalent
17. Li-ion
18. Mercury button
19. Lead storage
20. electro chemical
III. Match the following

Question.1

Answer:
i. $\mathrm{cd} \mathrm{ab}$
Question 2.

Answer:
ii. $c$ a d b
Question 3.

Answer:
iii. $\mathrm{d} \mathrm{c} \mathrm{ab}$
Question 4.

Answer:
iv. $\mathrm{c} \mathrm{a} \mathrm{d} \mathrm{b}$
Question 5.

Answer:
i. b c d a
Question 6.

Answer:
i. $\mathrm{c} \mathrm{a} \mathrm{b}$
IV. Assertion and reasons.
Question 1.
Assertion(A): If the temperature of the electrolytic solution increases, conductance also increases. Reason (R): Increase in temperature increases the kinetic energy of the ions and decreases the attractive force between the oppositely charged ions and hence conductivity increases.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
(b) Both $A$ and $R$ are wrong
(c) $A$ is correct but $R$ is wrong
(d) $\mathrm{A}$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
Question 2.
Assertion(A): Molar conductance of a solution increases with increase in dilution.
Reason (R): For a strong electrolyte, inter ionic forces of attraction decreases with dilution and so conductivity increases. For a weak electrolyte, degree of dissociation increases with dilution and conductivity increases.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$.
(b) $A$ and $\mathrm{R}$ are wrong
(c) $\mathrm{A}$ is correct but $\mathrm{R}$ is not the explanation of $\mathrm{A}$
(d) $\mathrm{A}$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
Question 3.
Assertion(A): AC current is used in wheatstone bridge arrangement to measure conductivity of ionic solution.
Reason (R): If DC current is used in wheatstone bridge arrangement, it will lead to electrolys is of the solution taken in the cell. So AC current is used to prevent electrolysis.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
(b) Both $A$ and $R$ are wrong
(c) $A$ is correct but $R$ is wrong
(d) A is wrong but R is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$

Question 4.
Assertion(A): Strong electrolytes have low molar conductivity at high concentration.
Reason (R): For a strong electrolyte, at high concentration, the number of constituent ions of the electrolyte is high and hence the attractive force between the oppositely charged ions is also high
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
(b) $A$ is correct but $R$ is wrong
(c) $A$ is wrong but $\mathrm{R}$ is correct
(d) Both $A$ and $\mathrm{R}$ are wrong
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
Question 5.
Assertion(A): In Daniel cell, the salt bridge contains an agar-agar gel mixed with an inert electrolyte $\mathrm{KCl}$ (or) $\mathrm{Na}_2 \mathrm{SO}_4$
Reason $(\mathrm{R})$ : The ions of inert electrolyte do not react with other ions present in half cells and they are not either oxidised or reduced at electrodes.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
(b) Both $A$ and $R$ are wrong
(c) $A$ is correct but $\mathrm{R}$ is wrong
(d) $A$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
Question 6.
Assertion(A): Current stops flowing when $\mathrm{E}_{\text {cell }}=0$
Reason (R): At $\mathrm{E}_{\text {cell }}=0$, Equilibrium of the cell reaction is attained.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
(b) Both $A$ and $R$ are wrong
(c) $A$ is correct but $\mathrm{R}$ is wrong
(d) $A$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
Question 7.
Assertion(A): Copper Sulphate can be stored in a Zinc vessel.
Reason (R): Zinc is less reactive than Copper.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
(b) Both $A$ and $R$ are wrong
(c) $\mathrm{A}$ is correct but $\mathrm{R}$ is wrong
(d) $A$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both A and R are correct

Question 8.
Assertion(A): Copper Sulphate can be stored in a Zinc vessel.
Reason (R): Zinc is less reactive than Copper.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
(b) Both $\mathrm{A}$ and $\mathrm{R}$ are wrong
(c) $\mathrm{A}$ is correct but $\mathrm{R}$ is wrong
(d) $A$ is wrong but $R$ is correct
Answer:
(b) Both $\mathrm{A}$ and $\mathrm{R}$ are wrong
Question 9 .
Assertion(A): As a lead storage battery gets discharged. density of electrolyte present in it decreases.
Reason (R): Lead and Lead dioxide both react with sulphuric acid to form lead sulphate.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
(b) $\mathrm{A}$ is correct but $\mathrm{R}$ is wrong
(c) $A$ is wrong but $\mathrm{R}$ is correct
(d) Both $A$ and $R$ are wrong.
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct
Question 10.
Assertion(A): The cell potential of mercury cell is $1.35 \mathrm{~V}$ which remains constant.
Reason (R): In mercury cell, the electrolyte is a paste of $\mathrm{KOH}$ and $\mathrm{ZnO}$.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct, but $\mathrm{R}$ is not the correct explanation of $\mathrm{A}$
(b) Both $\mathrm{A}$ and $\mathrm{R}$ are correct, but $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
(c) $A$ is wrong but $\mathrm{R}$ is correct
(d) $\mathrm{A}$ is correct but $\mathrm{R}$ is wrong
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct, but $\mathrm{R}$ is not the correct explanation of $\mathrm{A}$
Question 11 .
Assertion(A): If an iron rod is dipped in $\mathrm{CuSO}_4$ solution, then blue colour of the solution turns red.
Reason (R): Iron is more reactive than copper and so iron displaces copper from $\mathrm{CuSO}_4$ solution.
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$
(b) Both $\mathrm{A}$ and $\mathrm{R}$ are wrong
(c) $A$ is correct but $\mathrm{R}$ is wrong
(d) $\mathrm{A}$ is wrong but $\mathrm{R}$ is correct
Answer:
(a) Both $\mathrm{A}$ and $\mathrm{R}$ are correct and $\mathrm{R}$ is the correct explanation of $\mathrm{A}$

V. Find the odd one out and give the reasons.
Question 1.
(a) I $\alpha \mathrm{V}$
(b) $\mathrm{I}=\frac{V}{R}$
(c) $\mathrm{V}=\mathrm{IR}$
(d) $\mathrm{R}=\frac{I}{V}$
Answer:
(d) $\mathrm{R}$ is the odd one, and other three represents Ohm's law
Question 2 .
(a) $m=$ Zit
(b) $\mathrm{Z}=\frac{m}{I t}$
(c) $\mathrm{m} \alpha$ It
(c) $\frac{\mathrm{m}_1}{\mathrm{Z}_1} \$=\$ \frac{\mathrm{m}_2}{\mathrm{Z}_2}$
Answer:
(d) $\frac{m_1}{Z_1} \$=\$ \frac{m_2}{Z_2}=$ is the odd one, all the others are Faraday's I law but (ci) is Faraday's $¡ I$ law
Question 3.
(a) Pacemaker
(b) electronic watches
(c) trains
(d) cameras
Answer:
(c) train, Lead storage battery is used in trains, but in all others mercury button cell is used up.
Question 4.
(a) Automobiles
(b) Pacemaker
(c) Train
(d) Inverters
Answer:
(b) Pacemaker. In pacemaker mercury button cell is used whereas in other three, lead storage battery is used up.

Question 5.
(a) Cellular phone
(b) Laptop
(c) Digital Camera
(d) Electronic watch
Answer:
(d) Electronic watch. jn this mercury button cell is used whereas in others Li-ion battery is used up.
2 Mark Questions and Answers
VI. Answer the following.
Question 1.
State Ohm's law.
Answer:
At a constant temperature, the current flowing through the cell (I) is directly proportional to the voltage across the cell (V).
$
\begin{aligned}
& \mathrm{I} \alpha \mathrm{V}\left(\text { or) } \mathrm{I}=\frac{V}{R}\right. \\
& \mathrm{V}=\mathrm{IR}
\end{aligned}
$
Question 2.
Define Resistivity. Give its unit.
$\mathrm{p}$ (rho) is called the specific resistance (or) resistivity and it is defined as the resistance of an electrolyte confined between two electrodes having unit cross sectional area and are separated by a unit distance. Unit of resistivity is $\mathrm{Ohm}$ metre $(\Omega \mathrm{m})$
Question 3.
Define conductance and give its unit.
Answer:
The reciprocal of the resistance $\left(\frac{1}{2}\right)$ is known as the conductance of an electrolytic solution.
The SI unit of conductance is $\mathrm{Ohm}^{-1}$ (or) Siemen (S)

Question 4.
Define specific conductance. Give its SI unit.
Answer:
The specific conductance is defined as the conductance of a cube of an electrolytic solution of unit dimensions. The SI unit of specific
$
\mathrm{k}=\mathrm{C} \cdot \frac{l}{A}
$
conductance is $\mathrm{Sm}^{-1}$
Question 5.
What Is meant by resistance? Give its unit.
Answer:
Resistance is the opposition that a cell offers to the flow of electric current through it.
$\mathrm{R} \alpha \frac{l}{A}$
The SI unit of $\mathrm{R}=\mathrm{Ohm}(\Omega)$
Question 6.
What is molar conductance? Give its SI unit.
Answer:
The conductance of a conductivity cell in which the electrodes are separated by $1 \mathrm{~m}$ and having $\mathrm{V} \mathrm{m}^3$ of electrolytic solution that contains 1 moIe of an electrolyte is known as molar conductance.
$\Lambda_{\mathrm{m}}=\mathrm{kx} \mathrm{V}$
The SI unit of $\Lambda_{\mathrm{m}}=\mathrm{S} \mathrm{m} \mathrm{mol}^{-1}$
Question 7.
Define equivalent conductance. Give its SI unit.
Answer:
Equivalent conductance is defined as the conductance of ' $\mathrm{V}$ ' $\mathrm{m}^3$ of electrolytic solution containing one gram equivalent of electrolyte in a conductivity cell in which the electrodes are one metre apart.
$\Lambda=\frac{\kappa \times 10^{-3}}{N}$
The SI unit of $\mathrm{A}=\mathrm{S} \mathrm{m}^2$ gm equivalent'
Question 8 .
What are electro chemical cells? Mention its types.
Answer:
Electro chemical cell is a device which inter converts chemical energy into electrical energy and vice versa. It consists of two separate electrodes which are in contact with an electrolyte solution. Electro chemical cells are classified into two types.
1. Galvanic cell and
2. Electrolytic cell.

Question 9.
Distinguish between galvanic cell and electrolytic cell.
Answer:
Galvanic Cell
1. It is a device in which a spontaneous chemical reaction generates an electric current.
2. It converts chemical energy into electrical energy. It is commonly known as Battery.
3. e.g., Daniel cell, Dry cell.
4. A salt bridge is used in this.
Electrolytic cell
1. It is a device in which an electric current from an external source drives a non spontaneous reaction
2. It converts electrical energy into chemical energy.
3. e.g., Electrolysis of molten $\mathrm{NaCI}$.
4. Na salt bridge is used.
Question 10.
What is meant by Faraday? How is it calculated?
Answer:
One Faraday is defined as the charge of one mole of electron.
Charge of one electron $=1.6 \times 10^{-19} \mathrm{C}$
Charge of 1 mole of electrons $=6.023 \times 10^{23} \times 1.602 \times 10^{-19} \mathrm{C}$
$=6.023 \times 10^{23} \times 1.602 \times 10^{-19} \mathrm{C}$
$=96488 \mathrm{C}$
i.e., $\mathrm{IF} \simeq 965 \mathrm{O} 0 \mathrm{C}$
Question 11.
Define corrosion. Give one example.
Answer:
The redox process which causes the deterioration of metal is called corrosion. Rusting of iron is an example of corrosion. It is an electro chemical process.
Question 12.
Can you store copper sulphate solution in a zinc pot?
Answer:
Zinc is more reactive than copper. Hence, it displaces copper from copper sulphate solution as follows $\mathrm{Zn}(\mathrm{s})+\mathrm{CuSO}_4(\mathrm{aq}) \rightarrow \mathrm{ZnSO}_4(\mathrm{aq})+\mathrm{Cu}$ (s) So, we cannot store copper sulphate solution in a zinc pot.

Question 13.
Why does the conductivity of a solution decrease with dilution?
Answer:
Conductivity of a solution is the conductance of ions present in a unit volume of solution. On dilution the number of ions per unit volume decreases. Hence, the conductivity decrease.
Question 14.
Suggest a way to determine $10 \mathrm{~m}$ value of water.
$
\lambda_{\mathrm{m}}^{\circ}\left(\mathrm{H}_2 \mathrm{O}\right)=\lambda_{\mathrm{H}^{+}}+\lambda_{\mathrm{OH}^{-}}
$
We find out
$
\lambda_m^{\circ}(\mathrm{HCl}), \lambda_m^{\circ}(\mathrm{NaOH}) \text { and } \lambda_{\mathrm{m}}^{\circ}(\mathrm{NaCl})
$
Then
$
\lambda_{\mathrm{m}}^{\circ}\left(\mathrm{H}_2 \mathrm{O}\right)=\lambda_{\mathrm{m}}^{\circ}(\mathrm{HCl})+\lambda_{\mathrm{m}}^{\circ}(\mathrm{NaOH})-\lambda_{\mathrm{m}}^{\circ}(\mathrm{NaCl})
$

Question 15.
Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging? .

Answer:
A lead storage battery consists of anode made up of lead, cathode made up of grid of lead packed with lead dioxide $\left(\mathrm{PbO}_2\right)$ and $38 \%$ solution of sulphuric acid is used as an electrolyte. When the battery is in use, the following reaction take place:
Anode: $\mathrm{Pb}(\mathrm{s})+\mathrm{SO}_4^{2-}(\mathrm{aq}) \rightarrow \mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{e}^{-}$
Cathode $: \mathrm{PbO}_2(\mathrm{~s})+\mathrm{SO}_4{ }^{--}(\mathrm{aq})+4 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{H}_2 \mathrm{O}(1)$
On charging the battery, the reverse reaction takes place, i.e. $\mathrm{PbSO}_4$ deposited on the electrode is converted back into $\mathrm{Pb}$ and $\mathrm{PbO}_2$ and $\mathrm{H}_2 \mathrm{SO}_4$ regenerated.
Question 16.
What is meant by cell constant?
Answer:
Cell constant is the ratio of the distance between the electrodes (1) and the area of cross-section (A). It is denoted by 1 . Its unit is $\mathrm{cm}^{-1}$. Its SI unit is $\mathrm{m}^{-1}$.
Question 17.
State two advantages of $\mathrm{H}_2-\mathrm{O}_2$ fuel cell over ordinary cells.
Answer:
1. It is highly efficient.
2. It is pollution free
Question 18.
Why $\mathrm{Om}$ for $\mathrm{CH}_3 \mathrm{COOH}$ cannot be determined experimentally?
Answer:
Molar conductivity of weak electrolytes keeps on increasing with dilution and does not become constant even at very large dilution.
Question 19.
Which will have greater molar conductivity and why?
Answer:
Sol. (A) $1 \mathrm{~mol} \mathrm{KCI}$ dissolved in $200 \mathrm{cc}$ of the solution.
Sol. (B) $1 \mathrm{~mol} \mathrm{KCI}$ dissolved in $500 \mathrm{cc}$ of the solution.
Sol. (B) will have greater molar conductivity because
$
\lambda_{\mathrm{m}}=\mathrm{k} \times \mathrm{V}
$
with dilution $\mathrm{K}$ decreases but $\mathrm{V}$ increases, so that product will increase more.

Question 20.
Raju and his father were going in a boat in the river. Raju's father was going to throw away the cell used in watches and hearing aids into the water. Raju prevented him doing so.
1. As a student of chemistry, why would you advise Raju's father not to throw the cell in the water body?
2. What is the value associated with the above decision?
Answer:
1. The watch cells are made up of mercury. This mercury will pollute the water. Water contaminated with mercury leads to accumulation of mercury in the body of fishes and other aquatic life.
2. It helps in keeping the environment safe from pollution due to mercury.
3 Mark Questions And Questions
VII.Answer the following questions.
Question 1.
Explain about conductivity cell with an example.
Answer:
1. Sodium chloride (or) potassium chloride is dissolved in a solvent like water, the electrolyte is completely dissociated to give its constituent ions (cations and anions).
2. When an electric field is applied to such an electrolytic solution, the ions present in the solution carry charge from one electrode to another. PLattnium electrode and thereby they conduct electricity. electrode
3. The conductivity of the electrolytic solution is measured using a conductivity cell, solution

Question 2.
Explain about the factors affecting electrolytic conductance. Conductivily Cell

Answer:
1. If the interionic attraction between the oppositely charged ions ofsolute increases, the conductance will decrease.
2. Solvent of high dielectric constant show high conductance in solution.
3. Conductance is inversely proportional to the viscosity of the medium. i.e., conductivity increases with the decrease in viscosity.
4. If the temperature of the electrolytic solution increases, conductance also increases.
5. Molar conductance of a solution increases with increase in dilution. This is because, for a strong electrolyte, inter ionic force of attraction decrease with dilution.
6. For a weak electrolyte, degree of dissociation increases with dilution.
Question 3.
Explain about the variation of molar conductivity with concentration by Kohiraush studies?
Answer:
Kohiraush observed that, increase of molar conductance of an electrolytic solution with the increase in dilution. He deduced the following empirical relationship between the molar conductance $\left(\Lambda_{\mathrm{m}}\right)$ and
concentration of the
$
\Lambda_{\mathrm{m}}=\Lambda_{\mathrm{m}}^0-\mathrm{k} \sqrt{c}
$
For strong electrolytes such as $\mathrm{KCl}, \mathrm{NaCl}$ the plot $\Lambda_{\mathrm{m}} V_{\mathrm{s}} \sqrt{c}$, gives a straight line. It is also observed that the plot is not a linear one for weak electrolyte.

Question 4 .
For strong electrolytes the molar conductivity increases on dilution and reaches a maximum value at infinite dilution. Justify this statement.
Answer:
For a strong electrolyte, at high concentration, the number of constituent ions of the electrolyte in a given volume is high and hence the attractive force between the oppositely charged ions is also high. The ions also experienced a viscous drag due to greater solvation. These factors attribute for the low molar conductivity at high concentration.
When the dilution increases, the ions are far apart and the attractive forces decreases. At infinite dilution, the ions are so far apart, the interaction between them becomes insignificant and hence the molar conductivity increases and reaches a maximum value at infinite dilution.
Question 5.
For weak electrolyte, sudden increase In molar conductance with dilution. Prove this statement.
Answer:
For a weak electrolyte, at high concentration the plot is almost parallel to concentration axis with slight increase in conductivity as the dilution increases. When the concentration approaches zero, there is a sudden increase in the molar conductance and the curve is almost parallel to Am axis. This is due to the fact that the dissociation of the weak electrolyte increases with the increase in dilution (Ostwald's dilution law).
Question 6.
Explain about Debye-Huckel and Onsagar equation
Answer:
The influence of ion-ion interactions on the conductivity of strong electrolytes was studied by Debye and Huckel
They considered that each ion is surrounded by an ionic atmosphere of opposite sign, and derived an expression relating the molar conductance of strong electrolytes with the concentration by It was further developed by Onsagar. For a uni - univalent electrolyte the Debye Huckel and Onsagar equation is given below.
$
\Lambda_{\mathrm{m}}=\Lambda_{\mathrm{m}}^{\circ}\left(\mathrm{A}+\mathrm{B} \Lambda^{\circ} \mathrm{m}\right) \sqrt{c}
$
Where A and B are constants which depend only in the nature of the solvent and temperature.

Question 7.
What are the values of $\mathrm{A}$ and $\mathrm{B}$ in Debye Huckel and Onsagar equation?
Answer:
Debye Huckel and Onsagar equation is
$
\Lambda_{\mathrm{m}}=\Lambda_{\mathrm{m}}\left(\mathrm{A}+\mathrm{B} \Lambda^{\circ} \mathrm{m}\right) \sqrt{c}
$
Where
$
\begin{aligned}
& \mathrm{A}=\frac{82.4}{\sqrt{\mathrm{DTn}}} \\
& B=\frac{8.20 \times 10^5}{3 \sqrt{D T}} \\
& \mathrm{D}=\text { Dielectric constant of the medium } \\
& \eta=\text { Viscosity of the medium } \\
& \mathrm{T}=\text { Temperature in Kelvin }
\end{aligned}
$

Question 8 .
How will you calculate degree of dissociation of weak electrolytes and dissociation constant using Kohlrausch's law?
Answer:
1. The degree of dissociation of weak electrolyte can be calculated from the molar conductivity at a given concentration and the molar conductivity in infinite dilution using the formula
2. According to Ostwald's dilution law $\mathrm{K}_{\mathrm{a}}=\frac{\alpha^2 C}{1-\alpha}$
Substituting a value in the above equation
$
\mathrm{K}_{\mathrm{a}}=\frac{\Lambda_{\mathrm{m}}^2 \cdot \mathrm{C}}{\Lambda_{\mathrm{m}}^2 \cdot\left[1-\frac{\Lambda_{\mathrm{m}}}{\Lambda_{\mathrm{m}}^0}\right]} \Rightarrow \mathrm{K}_{\mathrm{a}}=\frac{\Lambda_{\mathrm{m}}^2 \mathrm{C}}{\Lambda_{\mathrm{m}}^2 \cdot\left(\frac{\Lambda_{\mathrm{m}}^0-\Lambda_{\mathrm{m}}}{\Lambda_{\mathrm{m}}^0}\right)} \Rightarrow \mathrm{K}_{\mathrm{a}}=\frac{\Lambda_{\mathrm{m}}^2 \mathrm{C}}{\Lambda_{\mathrm{m}}^{\circ} \cdot\left(\Lambda_{\mathrm{m}}^0-\Lambda_{\mathrm{m}}\right)}
$

Question 9.
How would you calculate the solubility of sparingly soluble salt using Kohlrausch's law?

Answer:
1. Substances like $\mathrm{AgCl}, \mathrm{PbSO}_4$ are sparingly soluble in water. The solubility product can be determined using conductivity experiments.
2. Let us consider $\mathrm{AgCl}$ as an example
$
\begin{aligned}
& \mathrm{AgCI}_{(\mathrm{s})} \rightarrow \mathrm{Ag}^{+}+\mathrm{Cl}^{-} \\
& \mathrm{K}_{\mathrm{sp}}=\left[\mathrm{Ag}^{+}\right]\left[\mathrm{Cl}^{-}\right]
\end{aligned}
$
3. Let the concentration of $\left[\mathrm{Ag}^{+}\right]$be ' $\mathrm{C}$ ' $\mathrm{mol} \mathrm{L}^{-1}$.
If $\left[\mathrm{Ag}^{+}\right]=\mathrm{C}$, then $\left[\mathrm{Cl}^{-}\right]$is also equal to $\mathrm{C} \mathrm{mol} \mathrm{L}^{-1}$.
$\mathrm{K}_{\mathrm{sp}}=\mathrm{C} . \mathrm{C}$
$\mathrm{K}_{\mathrm{sp}}=\mathrm{C}^2$.
4. The relationship between molar conductance and equivalent conductance is
$
\Lambda_0=\frac{\kappa \times 10^{-3}}{\mathrm{C}\left(\mathrm{molL}^{-1}\right)} \text { (or) } \mathrm{C}=\frac{\kappa \times 10^{-3}}{\Lambda^{\circ}}
$
Substitute the concentration value in the relation $\mathrm{K}_{\mathrm{sp}}=\mathrm{C}^2$
$
\mathrm{K}_{\mathrm{sp}}=\left[\frac{\kappa \times 10^{-3}}{\Lambda^{\circ}}\right]^2
$

Question 10.
What is the relationship between molar mass and electro chemical equivalent. Derive the equation.

Answer:
1. Consider the following general electro chemical redox reaction
$
\mathrm{M}^{\mathrm{n}+}(\mathrm{aq})+\mathrm{ne}^{-} \rightarrow \mathrm{M}_{(\mathrm{s})}
$
2. We can infer from the above equation that ' $n$ ' moles of electrons are required to precipitate
3. The quantity of charge required to precipitate 1 mole of $M^{n+}=$ Charge of ' $n$ ' moles of electrons $=n F$
4. In other words, the mass of the substance deposited by one coulomb of charge. Molar mass (M) Electro chemical equivalent $\mathrm{M}^{\mathrm{n}+}=\frac{\text { Molar mass }(\mathrm{M})}{\mathrm{n}(96500)}$
(or)
$
\mathrm{Z}=\frac{\text { Equivalent mass }}{96500}
$

Question 11.
What is meant by standard reduction potential? What is its application?
Answer:
1. The standard reduction potential $\left(\mathrm{E}^{\circ}\right)$ is a measure of the oxidising tendency of the species.
2. The greater the $E^{\circ}$ value means greater is the tendency shown by the species to accept electrons and undergo reduction.
3. So higher the $\mathrm{E}^{\circ}$ values, lesser is the tendency to undergo corrosion.
Question 12.
What is meant by Electro chemical series? Mention the top most and the least placed element in that series.
Answer:
1. The standard aqueous electrode potential at $298 \mathrm{~K}$ for various metal-metal ion electrodes are arranged in the decreasing order of their standard reduction potential values is known as electro chemical series.
2. The strongest reducing agent is $\mathrm{Li}$ which has $\mathrm{E}^{\circ}$ value as -3.05 and it is in bottom of the series.
3. The strongest oxidising agent is $F$ which has $\mathrm{E}^{\circ}$ value as +2.87 is the first element in that series.
Question 13.
Calculate the emf of the cell in which the following reaction takes place
$\mathrm{Ni}(\mathrm{s})+2 \mathrm{Ag}^{+}(0.002 \mathrm{M})-{ }^{\prime} \mathrm{Ni}^{2+}(0.160 \mathrm{M})+2 \mathrm{Ag}(\mathrm{s})$
Given that $\mathrm{E}^{\circ}$ cell $=1.05 \mathrm{~V}$
Answer:
Applying Nernst equation to the given cell reaction:

$
\begin{aligned}
& \mathrm{E}_{\text {cell }}=\mathrm{E}_{\text {cell }}^{\circ}-\frac{0.0591}{x} \log \frac{\mathrm{Ni}^{2+}}{\left[\mathrm{Ag}^{+}\right]^2}=1.05 \mathrm{~V}-\frac{0.0591}{2} \log \frac{0.160}{(0.002)^2} \\
&=1.05-\frac{0.0591}{2} \log \left(4 \times 10^4\right)=1.05-\frac{0.0591}{2} \times 4.6021 \\
&=1.05-0.14 \mathrm{~V}=0.91 \mathrm{~V}
\end{aligned}
$
Question 14.
If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?
Answer:
$\mathrm{Q}$ (coulomb) $=1$ (ampere) $\mathrm{xt}(\mathrm{sec})$
$=0.5$ ampere $\times 2 \times 60 \times 60=3600 \mathrm{C}$
A flow of IF, i.e., $96500 \mathrm{C}$ is equivalent to the flow of 1 mole of electrons
i.e., $6.023 \times 10^{23}$ electrons
$3600 \mathrm{C}$ is equivalent to flow of electrons
$=\frac{6.02 \times 10^{23}}{96500} \times 36002.246 \times 10^{22}$ electrons,
Question 15.
What are fuel cells? Write the electrode reactions of a fuel cell which uses the reaction of hydrogen with oxygen?
Answer:
A fuel cell is similar to a galvanic cell, it generates electricity directly by the electrochemical conversion of gaseous or liquid fuels fed into the cell as required.
At anode: $\mathrm{H}_2(\mathrm{~g})+2 \mathrm{OH}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})+2 \mathrm{e}^{-}$
At cathode: $\mathrm{O}_2(\mathrm{~g})+2 \mathrm{H}_2 \mathrm{O}(1)+4 \mathrm{e}^{-} \rightarrow 4 \mathrm{OH} \_$_(aq)
Overall reaction : $2 \mathrm{H}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})$

Question 18 .
How much copper is deposited on the cathode of an electrolytic cell If a current of 5 ampere is passed through a solution of copper sulphate for 45 minutes?
Answer:
[Molar mass of $\mathrm{Cu}=63.5 \mathrm{~g} \mathrm{~mol}^{-1}, \mathrm{IF}=96,500 \mathrm{C} \mathrm{mol}^{-1}$ ]
$\mathrm{Cu}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}(\mathrm{s})$
$\mathrm{m}=\mathrm{Z} \times \mathrm{xI}$
$=\frac{63.5}{2 \times 96500} \times 5 \mathrm{amp} \times 45 \times 60=\frac{857250}{193000}=4.44 \mathrm{~g}$
Question 19.
How much time would it take in minutes to deposit $1.18 \mathrm{~g}$ of metallic copper on a metal object when a current of $2.0 \mathrm{~A}$ is passed through the electrolytic cell containing $\mathrm{Cu}^{2+}$ ions?
Answer:
[Molar mass of $\mathrm{Cu}=63.5 \mathrm{~g} \mathrm{~mol}^{-1}, \mathrm{IF}=96,500 \mathrm{C} \mathrm{mol}^{-1}$ ]
$\mathrm{m}=\mathrm{Z} \times \mathrm{I} \times \mathrm{t}$
$1.18=\frac{63.5}{2 \times 96500}$
$\mathrm{t}=\frac{1.18 \times 2 \times 96500}{2 \times 63.5}$
$=1793.23 \mathrm{sec}$
$=\frac{1793.23}{60}=29.88 \mathrm{~min}$
Question 20.
What is a salt bridge? What is it used for?
Answer:
A salt bridge is a $\mathrm{U}$ - shaped tube containing concentrated solution of an inert electrolyte like $\mathrm{KCl}, \mathrm{KNO}_3$, $\mathrm{K}_2 \mathrm{SO}_4$, etc., or a solidified solution of an electrolyte such as agar-agar and gelatine. It is used,
1. To complete the electrical circuit by allowing ions to flow from one solution to the other without mixing the two solutions.
2. To maintain the electrical neutrality of the solutions in the two half cells.
Question 21.
Calculate emf of the following cell of $25^{\circ} \mathrm{C}$.
Answer:
$\mathrm{Fe}\left|\mathrm{Fe}^{2+}(0.001 \mathrm{M}) \| \mathrm{H}^{+}(0.01 \mathrm{M})\right| \mathrm{H}_2$ (g) (1 bar) $\mathrm{pt}$
$\mathrm{E}^0\left(\mathrm{Fe}^{2+} / \mathrm{Fe}\right)=-0.44 \mathrm{~V}$
$\mathrm{E}^0\left(\mathrm{H}^{+} / \mathrm{H}_2\right)=0.00 \mathrm{~V}$
Cell reaction
$
\begin{aligned}
& \mathrm{Fe}+2 \mathrm{H}^{+} \mathrm{Fe}^{2+}+\mathrm{H}_2 \\
& \mathrm{E}_{\text {cell }}^0=\mathrm{E}_{\text {cathode }}^0-\mathrm{E}_{\text {anode }}^0
\end{aligned}
$

suitable detector is connected between the junctions $\mathrm{B}$ and $\mathrm{D}$.

Schematic diagram of a conductivity cell in a wheatstone bridge circuit
4. The variable resistance $S$ is adjusted until the bridge is balanced and in this canditions, there is no current flow through the detector.
5. Under balanced condition
$\mathrm{P} / \mathrm{Q}=\mathrm{R} / \mathrm{S}$
$\mathrm{R}=\mathrm{P} / \mathrm{Q} \times \mathrm{S}$
The resistance of the electrolytic solution (R) is calculated from the known resistance values $P, Q$ and the measured $\mathrm{S}$ value using the equation (1).
6. Specific conductance (or) conductivity of an electrolyte can be calculated from the resistance value (R) using the following expression
7. The value of cell constant is usually provided by the cell manufacturer. Alternatively the cell constant may be determined using KCI solution whose concentration and specific conductance are known.
Question 2.
Explain about SHE (Standard Hydrogen Electrode).
Answer:
1. It is impossible to measure the emf of a single electrode, but we can $\mathrm{H}_2$ out $\mathrm{H}_2$ measure the potential difference between two electrodes $\left(\mathrm{E}_{\text {cell }}\right)$ using a voltmeter.
2. To calculate the emf of a single electrode, we need a reference electrode whose emf is known. For that purpose, Standard Hydrogen Electrode (SHE) is used as the reference electrode.
3. SHE has been assigned an orbitary emf of exactly zero volt.

4. It consists of platinum electrode in contact with $1 \mathrm{M} \mathrm{HC} 1$ solution and $1 \mathrm{~atm}$ hydrogen gas.
5. The hydrogen gas bubbled through the solution at $25^{\circ} \mathrm{C}$. $\mathrm{SHE}$ can act as cathode as well as an anode.
6. The Half cell reactions are given below:
If SHE is used as a cathode, the reduction reaction is $2 \mathrm{H}^2+2 \mathrm{e}^{-}+\mathrm{H}_{2(\mathrm{~g}, 1 \mathrm{~atm})} \mathrm{E}^{\circ}=0$ volt If SHE is used as an anode, the oxidation reaction is $\mathrm{H}_{2(\mathrm{~g}, 1 \mathrm{~atm})} 2 \mathrm{H}_{(\mathrm{aq}, 1 \mathrm{M})}^{+}+2 \mathrm{e}^{-} \mathrm{E}^{\circ}=0$ volt.

Question 3.
How would you determine the reduction potential of $\mathrm{Zn} / \mathrm{Zn}^{2+}$ (aq)? (or) How will you calculate the reduction potential of Half cell?
Answer:
1. Consider the zinc electrode dipped in zinc sulphate solution using SHE

2. Step 1:
The following galvanic cell is constructed using SHE
$
\mathrm{Zn}_{(\mathrm{s})} \mid \mathrm{Zn}^{2+} \text { (aq.1M) }\left|\mathrm{H}_{2(\mathrm{~g} \cdot 1 \mathrm{~atm})}\right| \mathrm{Pt}_{(\mathrm{s})}
$
3. Step 2 :
The emf of the above galvanic cell is measured using a voltmeter. In this case the measured emf of the above galvanic cell is $0.76 \mathrm{~V}$
4. Calculation:
We know that.
$
\begin{aligned}
& \mathrm{E}_{\text {cell }}^{\circ}=\left(\mathrm{E}^{\circ}{ }_{\mathrm{ox}}\right)_{\mathrm{Zn} \mid \mathrm{zn}^{2+}}+\left(\mathrm{E}_{\text {red }}^{\circ}\right)_{\mathrm{SHE}} \\
& \mathrm{E}^{\circ} \text { cell }=0.76+0 \mathrm{~V} \\
& =0.76 \mathrm{~V}
\end{aligned}
$
This oxidation potential corresponds to the below mentioned half cell reaction which takes place at the cathode
$
\mathrm{Zn} \rightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-} \text {(oxidation) }
$
(y) The emf of the reverse reaction will give the reduction potential
$
\begin{aligned}
& \mathrm{Zn}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Zn} \\
& \left.\left(\mathrm{E}^{\circ}{ }_{\mathrm{red}}\right)_{\mathrm{Zn}^{2+}}\right|_{\mathrm{zn}}=-0.76 \mathrm{~V}
\end{aligned}
$

Question 4.
Derive the relationship between Gibb's free energy and maximum work obtained from galvanic cell and equilibrium constant.
Answer:
1. In a galvanic cell, chemical energy is converted into electrical energy. The electrical energy produced by the cell is equal to the product of the total charge of the electrons and emf of the cell which drives these electrons between the electrodes.
2. If ' $n$ ' is the number of moles of electrons exchanged between the oxidising and reducing agent in the overall cell reaction, then the electrical energy produced by the cell is given as below.
Electrical energy $=$ change of ' $n$ ' moles of electrons $x E_{\text {cell }}$
Charge of I mole of electrons $=$ one Faraday $=1 \mathrm{~F}$
Charge of $\mathrm{n}$ moles of electrons $=\mathrm{nF}$
3. Electrical energy $=n \mathrm{nE}_{\text {cell }}$
This energy is used to do electric work. Therefore the maximum work that can be obtained from a galvanic cell is
Here the - ve sign is introduced to indicate that work is done by the system on the surroundings.
4. Second law of thermodynamics states that the maximum work done by the system is equal to the change in Gibbs free energy of the system
$\mathrm{W}_{\max }=\Delta \mathrm{G}$
5. $\Delta \mathrm{G}=-\mathrm{nFE}_{\text {cell }}(6)$
For a spontaneous cell reactions, the $\mathrm{AG}$ should be negative. The above expression indicates that $\mathrm{E}_{\text {cell }}$ should be positive to get a negative $A G$ value.
6. When all the cell components are in their standard state, the equation (6) becomes
$
\Delta \mathrm{G}^{\circ}=-\mathrm{nFE}^{\circ} \text { cell }
$
7. The standard free energy change is related to the equilibrium constant as per the following equation. $\Delta \mathrm{G}^{\circ}=-\mathrm{RT}$ In $\mathrm{K}_{\text {eq }}$ (8)
Comparing equations (7) and (8)
$\mathrm{nFE}^{\circ}$ cell $=\mathrm{RT}$ In $\mathrm{K}_{\text {eq }}$
(9)
$\mathrm{nFE}_{\text {cell }}^{\circ}=\frac{2.303 R T}{n F} \log \mathrm{K}_{\mathrm{eq}}$

Question 5.
Describe about the working principle of Leclanche cell.

Answer:

1. Leclanche cell:
Anode: Zinc container
Cathode: Graphite rod in contact with $\mathrm{MnO}_2$
Electrolyte: Ammonium chloride and Zinc chloride in water.
emf of the cell $=1.5 \mathrm{~V}$
2. Cell reaction:
Oxidation at anode
$\mathrm{Zn}_{(\mathrm{s})} \rightarrow \mathrm{Zn}^{2+}(\mathrm{aq})+2 \mathrm{e}_{-}$
Reduction at cathode
$
2 \mathrm{NH}_{4(\mathrm{aq})}^{+}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{NH}_{3(\mathrm{aq})}+\mathrm{H}_{2(\mathrm{aq})}
$
3. The hydrogen gas is oxidised to water by $\mathrm{MnO}_2$
$
\mathrm{H}_{2(\mathrm{~g})}+2 \mathrm{MnO}_{2(\mathrm{~s})} \rightarrow \mathrm{Mn}_2 \mathrm{O}_{3(\mathrm{~s})}+\mathrm{H}_2 \mathrm{O}_{(1)} \ldots \text {...(3) }
$
Adding equations $1,2,3$ the overall redox reaction
$
\mathrm{Zn}_{(\mathrm{s})}+2 \mathrm{NH}_{4(\mathrm{aq})}^{+}+2 \mathrm{MnO}_{2(\mathrm{~s})} \rightarrow \mathrm{Zn}^{2+}{ }_{(\mathrm{aq})}+\mathrm{Mn}_2 \mathrm{O}_{3(\mathrm{~s})}+\mathrm{H}_2 \mathrm{O}_{(1)}+2 \mathrm{NH}_3
$
4. The ammonia produced at the cathode combines with $\mathrm{Zn}^{2+}$ to form a complex ion $\left[\mathrm{Zn}\left(\mathrm{NH}_3\right)_4\right]_{2+}(\mathrm{aq})$.
As the reaction proceeds, the concentration of $\mathrm{NH}_4{ }^{+}$will decrease and the aqueous $\mathrm{NH}_3$ will increase which lead to the decrease in the emf of the cell.

Question 6.
Explain about the construction and uses of mercury button cell.
Answer:
1. Mercury button cell:
Anode: Zinc Amalgamated with mercury
Cathode: $\mathrm{HgO}$ mixed with graphite
Electrolyte: Paste of $\mathrm{KOH}$ and $\mathrm{ZnO}$.
2. Oxidation occurs at anode:
$
\mathrm{Zn}_{(\mathrm{s})}+2 \mathrm{OH}_{(\mathrm{aq})}^{-} \rightarrow \mathrm{ZnO}_{(\mathrm{s})}^{+2}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{l})}+2 \mathrm{e}^{-}
$
3. Reduction occurs at cathode
$
\begin{aligned}
& \mathrm{HgO}_{(\mathrm{s})}+\mathrm{H}_2 \mathrm{O}_{(1)}+2 \mathrm{e}^{-} \rightarrow \mathrm{Hg}_{(1)}+2 \mathrm{OH}_{(\mathrm{aq})}^{-} \\
& \mathrm{Hg}_{(\mathrm{s})}+2 \mathrm{OH}^{-}(\mathrm{aq})
\end{aligned}
$
Overall reaction is
$
\mathrm{Zn}_{(\mathrm{s})}+\mathrm{HgO}_{(\mathrm{s})} \rightarrow \mathrm{ZnO}_{(\mathrm{s})}+\mathrm{Hg}_{(1)}
$
4. Cell emf: about $1.35 \mathrm{~V}$

5. Uses:
It has higher capacity and longer life. It is used in pacemakers, electronic watches, cameras.
Question 7.
Describe about lead storage battery construction and its uses.
Answer:
Lead storage battery:
1. Anode - Spongy lead
Cathode - Lead plate bearing $\mathrm{PbO}_2$
Electrolyte $-38 \%$ by mass of $\mathrm{H}_2 \mathrm{SO}_4$ with density $1.2 \mathrm{~g} / \mathrm{ml}$
2. Oxidation occurs at the anode
$
\mathrm{Pb}_{(\mathrm{s})} \rightarrow \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-}
$
The $\mathrm{Pb}^{2+}$ ions combine with $\mathrm{SO}_4^{2-}$ to form $\mathrm{PbSO}_4$ precipitate
$
\mathrm{Pb}^{2+}(\mathrm{aq})+\mathrm{SO}_4^{2-} \rightarrow \mathrm{PbSO}_{4(\mathrm{~s})}
$
3. Reduction occurs at the cathode
$
\mathrm{PbO}_{2(\mathrm{~s})}+4 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow+2 \mathrm{H}_2 \mathrm{O}_{(1)}
$
The $\mathrm{Pb}^{2+}$ ions also combines with $\mathrm{SO}_4^{2-}$ ions to form sulphuric acid to form $\mathrm{PbSO}_4$ Precipitate
$
\mathrm{Pb}^{2+}(\mathrm{aq})+\mathrm{SO}_{2+}^{2-} \rightarrow \mathrm{PbSO}
$

4. The overall reaction is,
$
\begin{aligned}
& (1)+(2)+(3)+(4) \\
& \mathrm{Pb}_{(\mathrm{s})}+\mathrm{pbO}_{2(\mathrm{~s})}+4 \mathrm{H}^{+}{ }_{(\mathrm{s})}+2 \mathrm{SO}_{4(\mathrm{~s})}^{2-} \rightarrow 2 \mathrm{PbSO}_{4(\mathrm{~s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)}
\end{aligned}
$
5. The emf of a single cell is about 2V. Usually six such cells are combined in series to produce 12 volts.
6. The emf of the cell depends on the concentration of $\mathrm{H}_2 \mathrm{SO}_4$. As the cell reaction uses $\mathrm{SO}_4{ }^{2-}$ ions, the concentration $\mathrm{H}_2 \mathrm{SO}_4$ decreases. When the cell potential falls to about $1.8 \mathrm{~V}$, the cell has to be recharged.

7. Recharge of the cell - During recharge process, the role of anode and cathode is reversed and $\mathrm{H}_2 \mathrm{SO}_4$ is regenerated. Oxidation occurs at cathode (now anode)

Reduction occurs at anode (now cathode)
$
\mathrm{PbSO}_4(\mathrm{~s})+2 \mathrm{e}^{-} \rightarrow \mathrm{Pb}_{(\mathrm{s})}+\mathrm{SO}_{4(\mathrm{sq})}^{2-}
$
Overall reaction
$
2 \mathrm{pbSO}_{4(\mathrm{~s})}+2 \mathrm{H}_2 \mathrm{O}_{(1)} \rightarrow \mathrm{pb}_{(\mathrm{s})}+\mathrm{pbO}_2(\mathrm{~s})+4 \mathrm{H}^{+}(\mathrm{aq})+2 \mathrm{SO}^{2-} 4(\mathrm{aq})
$
The above reaction is exactly the reverse of redox reaction which takes place while discharging.
8. Uses: Lead storage battery is used in automobiles, trains, inverters.
Question 8.
Describe about lithium-ion battery and its uses.
Answer:
1. Lithium-ion battery
Anode - Porous graphite
Cathode - Transition metal oxide as $\mathrm{CoO}_2$
Electrolyte - Lithium salt in an organic solvent

2. At the anode oxidation occurs
$
\mathrm{Li}_{(\mathrm{s})} \rightarrow \mathrm{Li}_{(\mathrm{aq})}^{+}+\mathrm{e}^{-}
$
At the cathode reduction Occurs.
$
\mathrm{Li}^{+}+\mathrm{CoO}_{2(\mathrm{~s})}+\mathrm{e}^{-} \rightarrow \mathrm{LiCoO}_{2(\mathrm{~s})}
$
3. Overall reactions
$
\mathrm{Li}(s)+\mathrm{CoO}_2 \rightarrow \mathrm{Li} \mathrm{CoO}_{2(s)}
$
4. Both electrodes allow $\mathrm{Li}$ ions to move in and out of their structures. During discharge the $\mathrm{Li}$ ions produced at the anode moves towards cathode through the non-aquaeous electrolyte.
5. When a potential greater than the emf produced by the cell is applied across the electrode, the cell reaction is reversed and now the $\mathrm{Li}^{+}$ions move from cathode to anode where they become embedded on the porous electrode. This is known as intercalation.
6. Uses: This Li-ion battery is used in cellular phones, Laptop computer and digital camera.

Question 9.
What is corrosion? Explain about the electrochemical mechanism of corrosion.
Answer:
1. The metal is oxidised by oxygen in the presence of moisture. The redox process which causes the deterioration of metal is called corrosion.
2. Corrosion of iron is known as Rusting and it is an electrochemical process.
3. Electrochernical mechanism of corrosion - The formation of rust requires both oxygen and water. Since it is an electrochemical redox process, it requires both an anode and cathode in different places on the iron. The iron surface and a droplet of water on the surface form a tiny galvanic cell.
The region enclosed by water is exposed to low amount of oxygen and it act as anode. The remaining area has high amount of oxygen and it act as cathode. So based on oxygen amount, an electrochem leal cell is formed.
$
\begin{aligned}
& \mathrm{Fe}_{(\mathrm{s})} \rightarrow \mathrm{Fe}^{2+}{ }_{(\mathrm{aq})}+2 \mathrm{e}^{-} \\
& \mathrm{O}_{2(\mathrm{~g})}+4 \mathrm{H}_{(\mathrm{aq})}+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(1)}
\end{aligned}
$
4. At anode:
$
2 \mathrm{Fe}_{(\mathrm{s})} \rightarrow 2 \mathrm{Fe}^{2+}{ }_{(\mathrm{aq})}+4 \mathrm{e}^{-} \mathrm{E}^{\circ}=1.23 \mathrm{~V}
$
The electrons move through the iron metal from the anode to the cathode area where the oxygen dissolved in water is reduced to water.
5. At cathode:
The reaction of atmospheric carbondioxide with water gives carbonic acid which furnishes the $\mathrm{H}^{+}$ions for reduction.
$
\begin{aligned}
& \mathrm{O}_{2_{(\mathrm{s})}}+4 \mathrm{H}^{+}{ }_{(\mathrm{g})}+4 \mathrm{H}_{(\mathrm{aq})}^{+} \rightarrow 2 \mathrm{H}_2 \mathrm{O}_{(1)} \\
& \mathrm{E}^{\circ}=1.23 \mathrm{~V} \\
& =+1.67 \mathrm{~V}
\end{aligned}
$
6. The electrical circuit is completed by the migration of ions through water droplet. The overall redox reaction is

$\begin{aligned}
& 2 \mathrm{Fe}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{~g})}+4 \mathrm{H}^{+}{ }_{(\mathrm{aq})} \rightarrow 2 \mathrm{Fe}^{3+}{ }_{(\mathrm{aq})}+2 \mathrm{H}_2 \mathrm{O}(1) \\
& \mathrm{E}^{\circ}=0.44+1.23 \\
& =+1.67 \mathrm{~V}
\end{aligned}$

7. The positive emf value indicates that the reaction is spontaneous.
8. The $\mathrm{Fe}^{2+}$ ions are further oxidised to $\mathrm{Fe}^{3+}$ which on further reaction with oxygen to form rust.

Question 10 .
Explain about the various protection methods to prevent corrosion.
1. Coating metal surface by paint
2. Galvanizing - By Coating with another metal such as zinc. Zinc is stronger oxidising agent than iron and hence it can be more easily corroded than iron. i.e., instead of iron, zinc is oxidised.
3. Cathodic protection: In this technique, unlike galvanizing, the entire surface of the metal to be protected need not be covered with a protecting metal instead, metals such as $\mathrm{Mg}$ (or) $\mathrm{Zn}$ which is corroded more easily than iron can be used as sacrificial anode and the iron material act as cathode. So iron protected but $\mathrm{Mg}$ or $\mathrm{Zn}$ gets corroded.
4. Passivation - The metal is treated with strong oxidising agent such as Conc. $\mathrm{HNO}_3$. As a result, a protective layer is formed on the surface of the metal.
5. Alloy formation - The oxidising tendency of iron can be reduced by forming its alloy with other more anodic metals. Example - Stainless steel, an alloy of $\mathrm{Fe}$ and $\mathrm{Cr}$
Question 11.
(a) Give reasons for the following
- Rusting of iron is quicker in saline water than in ordinary water.
- Aluminium metal cannot be produced by the electrolysis of aqueous solution of aluminium salt.
(b) Resistance of a conductivity cell filled with $0.1 \mathrm{M} \mathrm{KCI}$ solution is $100 \mathrm{ohms}$. If the resistance of the sanie cell when filled with $0.02 \mathrm{M} \mathrm{KCI}$ solution is $520 \mathrm{ohms}$, calculate the conductivity and molar conductivity of $0.02 \mathrm{M} \mathrm{KCI}$ solution. Conductivity of $0.01 \mathrm{M} \mathrm{KCI}$ solution is $1.29 \mathrm{~S} \mathrm{~m}^{-1}$.
Answer:
(a)
1. It is because in saline water, there are inore $\mathrm{H}_4$ ions. Greater the number of $\mathrm{H}_4$ ions, quicker the rusting will take place.
2. It is because aluminium metal is more reactive than hydrogen and it will react with $\mathrm{H}_2 \mathrm{O}$.
(b)
Cell constant $=$ Conductivity (k) $\mathrm{x}$ Resistance (R)
$=1.29 \mathrm{~S} \mathrm{~m}^{-1} \times 100 \Omega$

$
\begin{aligned}
& =1.29 \mathrm{~m}^{-1}=1.29 \mathrm{~cm}^{-1} \\
& \lambda_{\mathrm{m}}=\frac{100 \mathrm{k}}{M} \\
& \mathrm{k}=\frac{1}{R} \times \frac{l}{A} \\
& \mathrm{k}=\frac{1}{520 \Omega} \times 1.29 \mathrm{~cm}^{-1}, \text { where } \\
& \mathrm{k}=2.48 \times 10^{-3} \mathrm{~S} \mathrm{~cm}^{-1} \\
& \lambda_{\mathrm{m}}=\frac{100 \times 0.248 \times 10^{-2}}{0.02} \\
& =124 \mathrm{~S} \mathrm{~cm}^2 \mathrm{~mol}^1
\end{aligned}
$
Question 12 .
1. State two advantages of $\mathrm{H}_2-\mathrm{O}_2$ fuel cell over ordinary cell.
2. Silver is electron deposited on a metallic vessel of total surface area $900 \mathrm{~cm}^2$ by passing a current of 0.5 amp for two hours. Calculate the thickness of silver metal deposited. [Given: Density of silver $=10.5 \mathrm{~g}$ $\mathrm{cm}^{-3}$ Atomic mass of silver $\left.=108 \mathrm{u} . \mathrm{IF}=96500 \mathrm{C} \mathrm{mol}^{-1}\right]$
Answer:
1.
- It is highly efficient and do not produce pollution.
- The $\mathrm{H}_2 \mathrm{O}$ so produced can be used by astronauts for drinking purpose.
2.
$
\begin{aligned}
& \mathrm{m}=\mathrm{Z} \times 1 \times \mathrm{t} \\
& \mathrm{m}=\frac{108}{96500} \times 0.5 \times 2 \times 60 \times 60 \\
& =\frac{108 \times 5}{965 \times 10} \times 2 \times 6 \times 6=4.03 \mathrm{~g} \\
& 4.03 \mathrm{~g}=\mathrm{V} \times \mathrm{d} \\
& 4.03 \mathrm{~g}=\mathrm{V} \times 10.5 \mathrm{~g} \mathrm{~cm}^{-3} \\
& \mathrm{~V}=\text { Area } \times \text { thickness } \\
& \mathrm{v}=4.03 \\
& =900 \mathrm{~cm}^2 \times \text { thickness } \\
& \text { Thickness }=\frac{4.03}{10.5} \\
& \frac{0.338 \mathrm{~cm}^3}{900 \mathrm{~cm}^2}=4.26 \times 10^{-4} \mathrm{~cm}
\end{aligned}
$
Question 13.
Distinguish between Leclanche cell and Lead storage battery.
Answer:
Leclanche Cell
1. It is a primary cell
2. It is a non-rechargeable cell
3. Anode: Zinc container
Cathode : Graphite rod in contact with $\mathrm{MnO}_2$

4. Electrolytes: Ammonium chloride and zinc chloride in water
5. Emf of the cell $=1.5 \mathrm{~V}$
Lead storage battery
1. It is a secondary cell
2. It is rechargeable cell
3. Anode : Spongy lead Cathode : Lead plate bearing $\mathrm{PbO}_2$
4. Electrolytes: $38 \%$ by mass of $\mathrm{H}_2 \mathrm{SO}_4$ with density $1.2 \mathrm{~g} / \mathrm{ml}$ 5. emf of the cell $2 \mathrm{~V}$.
Question 14.
Account for the following
1. Aluminium undergo slow corrosion than iron.
2. $\mathrm{H}_2-\mathrm{O}_2$ fuel cell js more useful than other cells.
Answer:
1. Aluminium, copper, silver also undergo corrosion but at a slower rate than iron. For eg., let us consider the reduction of Aluminium
$
\mathrm{Al}_{(\mathrm{s})} \rightarrow \mathrm{Al}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-}
$
$\mathrm{Al}^{3+}$ which reacts with oxygen in air to form a protective coating of $\mathrm{AI}_2 \mathrm{O}_3$. This coating act as a protective film for the inner surface. So further corrosion is prevented.
2. $\mathrm{H}_2-\mathrm{O}_2$ fuel cell is more advanced. Because it is highly efficient. it is pollution free. In this, $\mathrm{H}_2-\mathrm{O}_2$ fuel cell, energy of combustion of fuel is directly converted to electrical energy.
Common Errors
1. Units of electrical quantities may get confused.
2. Writing cell notation may be difficult.

Rectifications
1.Resistance - $\mathrm{R} \mathrm{ohm}(\Omega)$
Potential difference $-\mathrm{V}=$ Volt
Amount of current $-1=$ ampere
Specific resistance $(\mathrm{ohm} \mathrm{m})(\Omega \mathrm{m})$
Conductivity $=$ Siemen $=S$
Specific conductance $-\mathrm{k}=\mathrm{S} \mathrm{m}^{-1}$
Molar conductance $=\mathrm{S} \mathrm{m}^2 \mathrm{~mol}^{-1}$
Equivalent conductance $=\mathrm{S} \mathrm{m}^2$ gram equivalent ${ }^{-1}$
Cell constant $=\mathrm{m}^{-1}$
2. Easy way is (AC)
solid I aqueous solution II aqueous solution I soLid