NCERT Exemplar Class 12 Chemistry Chapter 3 Electrochemistry

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: MCQ (Type 1)

Question:1

Which cell will measure standard electrode potential of copper electrode?
$(i)Pt(s)|H_2(g,0.1bar)|H^{+}(aq.,1M)||C{u}^{2+}(aq.,1M)|Cu$
$(ii)Pt(s)|H_2(g,1bar)|H^{+}(aq.,1M)||C{u}^{+2}(aq.,2M)|Cu$
$(iii)Pt(s)|H_2(g,1bar)|H^{+}(aq.,1M)||C{u}^{2+}(aq.,1M)|Cu$
$(iv)Pt(s)|H_2(g,1bar)|H^{+}(aq.,0.1M)||C{u}^{2+}(aq.,1M)|Cu$

Answer:

The answer is the option (iii) On connecting copper electrode to standard hydrogen electrode, it acts as cathode and its standard electrode potential can be measured.
$E^0=E_R^0-E_L^0=E_R^0-0=E_R^0$
$Pt(s)|H_2(g,1bar)|H^{+}(aq.,1M)\parallel C{u}^{2+}(aq.,1M)\mid Cu$
will measure standard electrode potential of copper electrode.
The standard electrode potential is measured for a given cell by coupling it with the standard hydrogen electrode where pressure of hydrogen gas is maintained at one bar. Concentration of the H+ ion in the solution is one molar and so is the concentration of the oxidized and reduced forms of the species.

Question:2

Electrode potential for Mg electrode varies according to the equation
$E_{M{g}^{2+}/Mg}=E_{M{g}^{2+}/Mg}^{⊝}-\frac{0.0591}{2}log\frac{1}{[M{g}^{2+}]}$ The graph of $E_{M{g}^{2+}/Mg}$ Vs log $[M{g}^{2+}]$ is

Answer:

The answer is the option (ii) $E_{\frac{Mg2+}{Mg}}=E_{\frac{M{g}^{2+}}{Mg}}^o-\frac{0.059}{2}log[M{g}^{2+}]$
The given equation is that of a straight line with a positive slope and a non-zero intercept

Question:3

Which of the following statement is correct?
(i) E_Cell and ?_rG of cell reaction both are extensive properties.
(ii) E_Cell and ?_rG of cell reaction both are intensive properties.
(iii) E_Cell is an intensive property while ?_rG of cell reaction is an extensive property.
(iv) E_Cell is an extensive property while ?_rG of cell reaction is an intensive property.
Answer:

The answer is the option (iii) While E_cell is independent of the mass of species or the number of particles, it is an intensive property, whereas Δ_rG depends on the number of particles and is an extensive property.

Question:4

The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called ___________.
(i) Cell potential
(ii) Cell emf
(iii) Potential difference
(iv) Cell voltage
Answer:

The answer is the option (ii) when no current is drawn through the cell, the difference between the electrode potentials of two electrodes is EMF.

Question:5

Which of the following statement is not correct about an inert electrode in a cell?
(i) It does not participate in the cell reaction.
(ii) It provides surface either for oxidation or for the reduction reaction.
(iii) It provides a surface for conduction of electrons.
(iv) It provides a surface for a redox reaction.
Answer:

The answer is the option (iv) Inert electrodes act only as source or sink for electrons. They do not undergo redox reaction and merely provide the surface for the reaction.

Question:6

An electrochemical cell can behave like an electrolytic cell when ____________.
(i) E_cell = 0
(ii) E_cell > E_ext
(iii) E_ext > E_cell
(iv) E_cell = E_ext

Answer:

The answer is the option (iii) An electrochemical cell can behave like an electrolytic cell when there is an application of an external opposite potential on the galvanic cell and reaction is not inhibited until the opposing voltage reaches the value 1.1 V. No current flows through the cell when this happens. Reaction will function in the opposite direction on increasing the external potential any further.

Question:7

Which of the statements about solutions of electrolytes is not correct?
(i) The conductivity of the solution depends upon the size of ions.
(ii) Conductivity depends upon the viscosity of the solution.
(iii) Conductivity does not depend upon solvation of ions present in solution.
(iv) The conductivity of the solution increases with temperature.
Answer:

The answer is the option (iii) Conductivity decreases with an increasing salvation of ions.

Question:8

Using the data given below to find out the strongest reducing agent.
$E_{C{r}_{2}O{{}_7}^{2-}/C{r}^{3+}}^{⊝}=1.33V$
$E_{C{l}_2/C{l}^{-}}^{⊝}=1.36V$
$E_{MnO{{}_4}^{-}/M{n}^{2+}}^{⊝}=1.51V$
$E_{C{r}^{3+}/Cr}^{⊝}=-0.74V$
$(i)C{l}^{-}$
$(ii)Cr$
$(iii)C{r}^{3+}$
$(iv)M{n}^{+2}$
Answer:

The answer is the option $(ii)Cr$ is the strongest reducing agent as it is the only one with a negative standard reduction potential

Question:9

Use the data given in Q.8 and find out which of the following is the strongest oxidising agent.
$(i)C{l}^{-}$
$(ii)M{n}^{2+}$
$(iii)Mn{O}_4^{-}$
$(iv)C{r}^{3+}$
Answer:

The answer is the option (iii). Oxidizing capacity increases with a positive increase in the standard reduction potential. $Mn{O}^{4-}$ with the highest standard reduction potential is the strongest oxidizing agent.

Question:10

Using the data given in Q.8 find out in which option the order of reducing power is correct.
$(i)C{r}^{3+}<C{l}^{-}<M{n}^{2+}<Cr$
$(ii)M{n}^{2+}<C{l}^{-}<C{r}^{+3}<Cr$
$(iii)C{r}^{3+}<C{l}^{-}<C{r}_2{O}_7^{2-}<Mn{O}_4^{-}$
$(iv)M{n}^{2+}<C{r}^{3+}<C{l}^{-}<Cr$
Answer:

The answer is the option (ii). A decrease in reduction potential corresponds with an increase in reduction power. The order of reducing power is $(ii)M{n}^{2+}<C{l}^{-}<C{r}^{+3}<Cr$

Question:11

Use the data given in Q.8 and find out the most stable ion in its reduced form.
$(i)C{l}^{-}$
$(ii)C{r}^{3+}$
$(iii)Cr$
$(iv)M{n}^{2+}$
Answer:

The answer is the option (iv) Due to a higher $E^o$ value, $M{n}^{2+}$ is most stable in its reduced form.

Question:12

Use the data of Q.8 and find out the most stable oxidised species.
$(i)C{r}^{3+}$
$(ii)Mn{O}_4^{-}$
$(iii)C{r}_2{O}_7^{2-}$
$(iv)M{n}^{2+}$
Answer:

The answer is the option (i). Due to the lowest $E^o$value, $C{r}^{3+}$ is most stable in its oxidized form.

Question:13

The quantity of charge required to obtain one mole of aluminium from $A{l}_2{O}_3$ is ___________.
(i) 1F
(ii) 6F
(iii) 3F
(iv) 2F
Answer:

The answer is the option (iii) $A{l}_2{O}_3\to 2A{l}^{3+}+3O^{2-}$
$A{l}^{3+}+3e^{-}\to Al$ (for 1 mole)
To obtain 1 mole $Al$ from $A{l}_2{O}_3$, we require 3F charge

Question:14

The cell constant of a conductivity cell _____________.
(i) changes with the change of electrolyte.
(ii) changes with the change of concentration of electrolyte.
(iii) changes with the temperature of the electrolyte.
(iv) remains constant for a cell.
Answer:

The answer is the option (iv) The cell constant of a conductivity cell remains constant for a cell.

Question:15

While charging the lead storage battery ______________.
(i) $PbS{O}_4$ anode is reduced to $Pb$
(ii) $PbS{O}_4$ cathode is reduced to $Pb$
(iii) $PbS{O}_4$ cathode is oxidised to $Pb$
(iv) $PbS{O}_4$ anode is oxidised to $Pb{O}_2$
Answer:

The answer is the option (i)
Reduction at Anode: $PbS{O}_4(s)+2e^{-}\to Pb(s)+S{O}_4^{2-}(aq)(Reduction)$
Oxidation at Cathode: $PbS{O}_4(s)+2H_{2}O\to Pb{O}_2(s)+S{O}_4^{2-}+4H^{+}+2e^{-}$
Overall reaction : $2PbS{O}_4(s)+2H_{2}O\to Pb(s)+Pb{O}_2(s)+4H^{+}+2S{O}_4^{2-}$

Question:16

${\wedge }_{m(N{H}_{4}OH)}^0$ is equal to ______________.
$(i){\wedge }_{m(N{H}_{4}OH)}^0+{\wedge }_{m(N{H}_{4}Cl)}^0-{\wedge }_{(HCl)}^0$
$(ii){\wedge }_{m(N{H}_{4}Cl)}^0+{\wedge }_{m(NaOH)}^0-{\wedge }_{(NaCl)}^0$
$(iii){\wedge }_{m(N{H}_{4}Cl)}^0+{\wedge }_{m(NaCl)}^0-{\wedge }_{(NaOH)}^0$
$(iv){\wedge }_{m(NaOH)}^0+{\wedge }_{m(NaCl)}^0-{\wedge }_{(N{H}_{4}Cl)}^0$
Answer:

The answer is the option (ii) $N{H}_{4}Cl\rightleftharpoons N{H}_4^{+}+C{l}^{-}$
$NaCl\rightleftharpoons N{a}^{+}+C{l}^{-}$
$NaOH\rightleftharpoons N{a}^{+}+O{H}^{-}$
$N{H}_{4}OH\rightleftharpoons N{H}_4^{+}+O{H}^{-}$
${\wedge }_{m(N{H}_{4}Cl)}^0+{\wedge }_{m(NaOH)}^0-{\wedge }_{(NaCl)}^0$

Question:17

In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?

$(i)N{a}^{+}(aq)+e^{-}\to Na(s);E_{Cell}^o=-2.71V$

$(ii)2H_{2}O(l)\to O_2(g)+4H^{+}(aq)+4e^{-};E_{Cell}^o=1.23V$

$(iii)H^{+}(aq)+e^{-}\to \frac{1}{2}{H}_2(g);E_{Cell}^o=0.00V$

$(iv)C{l}^{-}(aq)\to \frac{1}{2}C{l}_2(g)+e^{-};E_{Cell}^o=1.36V$
Answer:

The answer is the option (ii) Upon electrolysis H₂O gives-

$2H_{2}O\to O_2+4H^{+}+4e^{-};E_{cell}^0=1.23V$

Since, $E_{cell}^0=1.23V$. Hence this half cell reaction occurs at anode.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: MCQ (Type 2)

Question:18

The positive value of the standard electrode potential of ${Cu^{2+} / Cu$ indicates that ____________.
(i) this redox couple is a stronger reducing agent than the ${H^{+}/{H_{2}}$ couple.
(ii) this redox couple is a stronger oxidising agent than ${H^{+}/{H_{2}}$.
(iii) $Cu$ can displace $H_2$ from acid.
(iv) $Cu$ cannot displace $H_2$ from acid.
Answer:

The answer is the option (ii, iv) Decrease in E° indicates an increase in reducing power
$$\begin{gathered} C{u}^{2+}+2e^{-}\to Cu;E^0=0.34V \\ 2H^{+}+2e^{-}\to H_2;E^0=0.00V \end{gathered}$$
As, E° value for $C{u}^{2+}$is higher -
(i) It is the stronger oxidizing agent
(ii) It can't displace $H_2$

Question:19

$E_{cell}^{\mathrm{\Theta }}$ for some half cell reactions are given below. Based on these mark the correct answer.
$(i)H^{+}(aq)+e^{-}\to \frac{1}{2}{H}_2(g);E_{cell}^o=0.00V$
$(ii)2H_{2}O(l)\to O_2(g)+4H^{+}(aq)+4e^{-};E_{cell}^o=1.23V$
$(iii)2S{O}_4^{2-}(aq)\to S_2{O}_8^{2-}(aq)+2e^{-};E_{cell}^o=1.96V$
(i) In dilute sulphuric acid solution, hydrogen will be reduced at the cathode.
(ii) In concentrated sulphuric acid solution, water will be oxidised at the anode.
(iii) In dilute sulphuric acid solution, water will be oxidised at the anode.
(iv) In dilute sulphuric acid solution, $S{O}_4^{2-}$ ion will be oxidised to tetrathionate ion at the anode.
Answer:

The answer is the option (ii, iii) In dilute sulphuric acid solution -
Reduction at cathode: $H^{+}+e^{-}\to \frac{1}{2}{H}_2$
Oxidation at anode : $2H_{2}O\to O_2+4H^{+}+4e^{-}$
In concentrated sulphuric acid solution, sulphate $(SO{{}_4}^{2-})$ ions oxidize to form tetrathionate $(S_{2}O{{}_8}^{2-})$ ions.

Question:20

$E_{Cell}^{\mathrm{\Theta }}=1.1V$ for Daniel cell. Which of the following expressions are correct description of state of equilibrium in this cell?
$(i)1.1=K_c$
$(ii)\frac{2.303RT}{2F}log{K}_c=1.1$
$(iii)log{K}_c=2.2/0.059$
$(iv)log{K}_c=1.1$
Answer:

The answer is the option (ii,iii)
$E_{cell}^0=\frac{2.303RT}{nF}log{K}_c=\frac{0.059}{2}log{K}_c$
$1.1=\frac{0.059}{2}log{K}_c$
$log{K}_c=\frac{2.2}{0.059}$

Question:21

Conductivity of an electrolytic solution depends on ____________.
(i) nature of electrolyte.
(ii) the concentration of electrolyte.
(iii) power of AC source.
(iv) distance between the electrodes.
Answer:

The answer is the option (i, ii). Mobile ions are responsible for the conductivity of electrolyte solution and this phenomenon is termed ionic conductance. It depends only on the following factors–

1. the nature of electrolyte added

2. size of the ion produced and their solvation

3. concentration of electrolyte

4. nature of solvent and its viscosity

5. temperature

Question:22

${\wedge }_{m(H_{2}O)}^0$ is equal to ______________.
$(i){\wedge }_{m(HCl)}^0+{\wedge }_{m(NaOH)}^0-{\wedge }_{m(NaCl)}^0$
$(ii){\wedge }_{m(HN{O}_3)}^0+{\wedge }_{m(NaN{O}_3)}^0-{\wedge }_{m(NaOH)}^0$
$(iii){\wedge }_{m(HN{O}_3)}^0+{\wedge }_{m(NaOH)}^0-{\wedge }_{m(NaN{O}_3)}^0$
$(iv){\wedge }_{m(N{H}_{4}OH)}^0+{\wedge }_{m(HCl)}^0-{\wedge }_{m(N{H}_{4}Cl)}^0$
Answer:

The answer is the option (i,iv)
${\wedge }_{m(H_{2}O)}^0={\wedge }_{m(HCl)}^0+{\wedge }_{m(NaOH)}^0-{\wedge }_{m(NaCl)}^0$
${\wedge }_{m(N{H}_{4}OH)}^0+{\wedge }_{m(HCl)}^0-{\wedge }_{m(N{H}_{4}Cl)}^0={\wedge }_{m(H_{2}O)}^0$
Molar conductivity of water is equal to the sum of the molar conductivities of constituent ions. However, $N{H}_{4}OH$ doesn’t undergo complete decomposition as it is a weak electrolyte.

Question:23

What will happen during the electrolysis of an aqueous solution of $CuS{O}_4$ by using platinum electrodes?
(i) Copper will deposit at the cathode.
(ii) Copper will deposit at the anode.
(iii) Oxygen will be released at anode.
(iv) Copper will dissolve at the anode.
Answer:

The answer is the option (i,iii)
$CuS{O}_4\rightleftharpoons C{u}^{2+}+S{O}_4^{2-}$
$H_{2}O\rightleftharpoons H^{+}+O{H}^{-}$
At cathode : $C{u}^{2+}+2e^{-}\to Cu;E_{cell}^0=0.34V$
$H^{+}+e^{-}\to \frac{1}{2}{H}_2;E_{cell}^0=0.00V$
At cathode, the reaction with higher $E^0$ is preferred
At anode :$2S{O}_4^{2-}-2e^{-}\to S_2{O}_8^{2-};E_{cell}^0=1.96V$
$2H_{2}O\to O_2+4H^{+}+4e^{-};E_{cell}^0=1.23V$
At anode, the reaction with lower $E^o$ is preferred.

Question:24

What will happen during the electrolysis of an aqueous solution of $CuS{O}_4$ in the presence of $Cu$ electrodes?
(i) Copper will deposit at the cathode.
(ii) Copper will dissolve at the anode.
(iii) Oxygen will be released at anode.
(iv) Copper will deposit at the anode.
Answer:

The answer is the option (i,ii)
At Cathode : $C{u}^{2+}+2e^{-}\to Cu(s)$
At anode : $Cu(s)\to C{u}^{2+}+2e^{-}$
Cathode will witness deposite of $Cu$ and Anode will witness its dissolution

Question:25

Conductivity κ , is equal to ____________.
$(i)\frac{1}{R}\frac{l}{A}$
$(ii)\frac{G^{\ast }}{R}$
$(iii){\wedge }_m$
$(iv)\frac{l}{A}$
Answer:

The answer is the option (i,ii)
$(i)\frac{1}{R}\frac{l}{A}$
$(ii)\frac{G^{\ast }}{R}$

Question:26

Molar conductivity of ionic solution depends on ___________.
(i) temperature.
(ii) distance between electrodes.
(iii) the concentration of electrolytes in solution.
(iv) the surface area of electrodes.
Answer:

The answer is the option (i, iii). Temperature and concentration of electrolytes determine the molar conductivity of an ionic solution

Question:27

For the given cell, $Mg\left|M{g}^{2+}\right|\left|C{u}^{2+}\right|Cu$
(i) $Mg$ is cathode
(ii) $Cu$ is cathode
(iii) The cell reaction is $Mg+C{u}^{2+}\to M{g}^{2+}+Cu$
(iv) Cu is the oxidising agent
Answer:

The answer is the option (ii, iii). At cathode, Cu is reduced and at anode, Mg is oxidized.
(ii) $Cu$ is cathode
(iii) The cell reaction is $Mg+C{u}^{2+}\to M{g}^{2+}+Cu$

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: Short Answer Type

Question:28

Can absolute electrode potential of an electrode be measured?

Answer:

No, absolute electrode potential of an electrode cannot be measured.

Question:29

Can $E_{cell}^{\mathrm{\Theta }}$ or ${\mathrm{\Delta }}_r{G}^{\mathrm{\Theta }}$ for cell reaction ever be equal to zero?

Answer:

$E^o$and $\mathrm{\Delta }{G}^o$can never be zero for a cell reaction.

Question:30

Under what condition is $E_{cell}=0$ or ${\mathrm{\Delta }}_{r}G=0?$
Answer:

Upon completely discharging or at equilibrium, $E_{cell}=0$ and ${\mathrm{\Delta }}_{r}G=0$.

Question:31

What does the negative sign in the expression $E_{Z{n}^{2+}/Zn}^{\mathrm{\Theta }}=-0.76V$ mean ?
Answer:

$E_{Z{n}^{2+}/Zn}^{\mathrm{\Theta }}=-0.76V$
Zinc has a higher reducing power than Hydrogen Sa it has a negative $E^0$ while it is zero for Hydrogen
$Zn+H_{2}S{O}_4\to ZnS{O}_4+H_2$

Question:32

Aqueous copper sulphate solution and aqueous silver nitrate solution are electrolysed by 1 ampere current for 10 minutes in separate electrolytic cells. Will, the mass of copper and silver, deposited on the cathode be the same or different? Explain your answer.
Answer:

According to Faraday's second law of electrolysis amount of different substance liberated by same quantity or electricity passes through electrolyte solution is directly proportional to their chemcial equivalent weight.
W₁/W₂=E₁/E₂
where, E₁ and E₂ have different values depending upon number of electrons required to reduce the metal ion.
Hence, massess of Cu and Ag deposited will be different.

Question:33

Depict the galvanic cell in which the cell reaction is $Cu+2A{g}^{+}\to 2Ag+C{u}^{2+}$
Answer:

$Cu\left|C{u}^{2+}\right|\left|A{g}^{+}\right|Ag$

Question:34

Value of standard electrode potential for the oxidation of $C{l}^{-}$ ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why is $C{l}^{-}$ oxidised at anode instead of water?

Answer:

Under the conditions of electrolysis of aqueous sodium chloride, oxidation of water at anode requires overpotential hence Cl^- is oxidised instead of water

Question:35

What is electrode potential?
Answer:

The electrical potential difference set up between the metal and its solution is called electrode potential.

Question:36

Consider the following diagram in which an electrochemical cell is coupled to an electrolytic cell. What will be the polarity of electrodes ‘A’ and ‘B’ in the electrolytic cell?


Answer:

‘A’ has negative and ‘B’ has positive polarity.

Question:37

Why is alternating current used for measuring the resistance of an electrolytic solution?
Answer:

Direct current will lead to electrolysis of the solution, which will change the concentration of ions in the solution. Use of Alternating current will prevent this from happening.

Question:38

A galvanic cell has an electrical potential of 1.1V. If an opposing potential of 1.1V is applied to this cell, what will happen to the cell reaction and current flowing through the cell?
Answer:

Cell reaction ceases if the opposing potential is equal to the electrical potential.

Question:39

How will the pH of brine (aq. NaCl solution) be affected when it is electrolyzed?
Answer:

Upon electrolysis of Brine solution, the following reactions take place:
Cathode :$2H^{+}+2e^{-}\to H_2$
Anode : $2C{l}^{-}\to C{l}_2+2e^{-}$
The remaining $N{a}^{+}$ and $O{H}^{-}$ ions are responsible for turning the solution basic and thus increase the pH.

Question:40

Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?

Answer:

The mercury cell has a constant cell potential throughout its useful life because the Ions are not involved in the overall cell reaction of mercury cells.

Question:41

Solutions of two electrolytes ‘A’ and ‘B are diluted. The ${\mathrm{\Lambda }}_m$ of ‘B’ increases 1.5 times while that of A increases 25 times. Which of the two is a strong electrolyte? Justify your answer.
Answer:

The lower increase of ${\wedge }_m$ for Electrolyte B is due to complete ionization of the same. Hence, It is the stronger electrolyte.

Question:42

When acidulated water (dil.$H_{2}S{O}_4$ solution) is electrolysed, will the pH of the solution be affected? Justify your answer.
Answer:

The following reaction occur :
At Anode : $2H_{2}O\to O_2+4H^{+}+4e^{-}$
At cathode : $4H^{+}+4e^{-}\to 2H_2(\uparrow )$
As the concentration of H⁺ ions is maintained, there will be no change in pH.

Question:43

In an aqueous solution how does specific conductivity of electrolytes change with the addition of water?
Answer:

Concentration of ions will decrease on addition of water, which in turn will reduce the electrical conductivity.

Question:44

Which reference electrode is used to measure the electrode potential of other electrodes?
Answer:

The standard hydrogen electrode is used as the reference electrode. For other electrodes, we measure the electrode potential considering the electrode potential for standard hydrogen electrode to be zero.

Question:45

Consider a cell given below
$Cu\left|C{u}^{2+}\right|\left|C{l}^{-}\right|C{l}_2,Pt$
Write the reactions that occur at anode and cathode.
Answer:

The given cell is :
$Cu(s)\left|C{u}^{2+}\right|\left|C{l}^{-}\right|C{l}_2(pt)$
Anode : $Cu(s)\to C{u}^{2+}+2e^{-}$
Cathode : $C{l}_2(g)+2e^{-}\to 2C{l}^{-}$

Question:46

Write the Nernst equation for the cell reaction in the Daniel cell. How will the E_Cell be affected when the concentration of $Z{n}^{2+}$ ions is increased?
Answer:

Daniel Cell :
$Zn(s)\left|Z{n}^{2+}\right|\left|C{u}^{2+}\right|Cu(s)$
Anode :$Zn(s)\to Z{n}^{2+}+2e^{-}$
Cathode : $C{u}^{2+}+2e^{-}\to Cu(s)$
Overall cell reaction : $Zn(s)+C{u}^{2+}\rightleftharpoons Z{n}^{2+}+Cu(s)$
$Q=\frac{[Z{n}^{2+}]}{[C{u}^{2+}]}$
$E_{cell}=E_{cell}^0-\frac{0.059}{2}log\frac{[Z{n}^{2+}]}{[C{u}^{2+}]}$
Therefore, with increasing concentration of $Z{n}^{2+}$, the cell potential decreases.

Question:47

What advantage do the fuel cells have over primary and secondary batteries?
Answer:

Primary battery come with limited number of reactants and can’t be reused once they are discharged. Secondary batteries take a considerable amount of time to recharge. Fuel cell is superior to both primary and secondary batteries as they operate without any breaks as long as you keep supplying the reactants

Question:48

Write the cell reaction of a lead storage battery when it is discharged. How does the density of the electrolyte change when the battery is discharged?
Answer:

During Discharge: $Pb+Pb{O}_2+2H_{2}S{O}_4\to 2PbS{O}_4+2H_{2}O$
As water is formed during the discharge process, the concentration of electrolyte reduces.

Question:49

Why on dilution the ${\wedge }_m$ of $C{H}_{3}COOH$ increases drastically, while that of $C{H}_{3}COONa$ increases gradually?
Answer:

For weak electrolytes like $C{H}_{3}COOH,$ on dilution, the concentration of ions increases due to the increase in degree of dissociation, but for strong electrolytes like $C{H}_{3}COONa$, the number of ions remain constant upon dilution

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: Matching Type

Question:50

Match the terms given in Column I with the units given in Column II.

Answer:

(i —> c), (ii —> d), (iii —> a), (iv —> b)

Question:51

Match the terms given in Column I with the items given in Column II.

Answer:

(i -> d), (ii -> a), (iii -> b), (iv -> c)

Question:52

Match the items of Column I and Column II.

Answer:

(i —> d), (ii -> c) (iii -> a), (iv -> b)

Question:53

Match the items of Column I and Column II.

Answer:

(i -> d), (ii -> c), (iii -> b), (iv -> a)

Question:54

Match the items of Column I and Column II.

Answer:

(i -> d), (ii -> c), (iii —> a, e), (iv -> b)

Question:55

Match the items of Column I and Column II on the basis of data given below:
$E_{F_2/F^{-}}^{⊝}=2.87V,$ $E_{L{i}^{+}/Li}^{⊝}=-3.5V,$ $E_{A{u}^{3+}/Au}^{⊝}=1.4V,$ $E_{B{r}_2/B{r}^{-}}^{⊝}=1.09V,$

Answer:

(i->c),(ii->a),(iii->g),(iv->e),(v->d),(vi->b),(vii->g,f)

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: Assertion and Reason Type

Question:56

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion:$Cu$ is less reactive than hydrogen.

Reason:$E_{C{u}^{2+}/Cu}^{⊝}$ is negative
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (iii) As $E_{C{u}^{2+}/Cu}^{⊝}$ is positive, Copper is less reactive than hydrogen.

Question:57

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion:$E_{Cell}$ should have a positive value for the cell to function.

Reason:$E_{cathode}<E_{anode}$
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (iii) $E_{cell}=E_{cathode}-E_{anode}$. To have a positive value of $E_{cell},E_{cathode}>E_{anode}$

Question:58

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: Conductivity of all electrolytes decreases on dilution.
Reason: On dilution number of ions per unit volume decreases.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (i) Upon dilution, the concentration of ions decreases and hence, conductivity also decreases.

Question:59

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: ${\wedge }_m$ for weak electrolytes shows a sharp increase when the electrolytic solution is diluted.
Reason: For weak electrolytes degree of dissociation increases with dilution of solution.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (i) Degree of dissociation of weak electrolytes increases on dilution, which results in a sharp increase in ${\wedge }_m$ values.

Question:60

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: Mercury cell does not give steady potential.
Reason: In the cell reaction, ions are not involved in solution.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (v). Mercury cell maintains a constant cell potential because the electrolyte isn’t consumed in the cell process

Question:61

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: Electrolysis of $NaCl$ solution gives chlorine at anode instead of $O_2$.
Reason: Formation of oxygen at anode requires overvoltage.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (i). Though the $E^o$ value for the formation of oxygen is lower than that for the formation of chlorine, it is not formed because it requires overvoltage.

Question:62

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: For measuring resistance of an ionic solution an AC source is used.
Reason: Concentration of ionic solution will change if DC source is used.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (i). Direct current will lead to electrolysis of the solution, which will change the concentration of ions in the solution. Use of Alternating current will prevent this from happening

Question:63

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: Current stops flowing when $E_{cell}=0.$
Reason: Equilibrium of the cell reaction is attained.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (i) At equilibrium, $E_{cell}=0$ and no current flows.

Question:64

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion:$E_{A{g}^{+}/Ag}$ increases with increase in concentration of $A{g}^{+}$ ions.
Reason:$E_{A{g}^{+}/Ag}$ has a positive value.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion

Question:65

In the following question, a statement of Assertion (i) followed by a statement of Reason (R) is given. Choose the correct option out of the following choices:
Assertion: Copper sulphate can be stored in zinc vessel.
Reason: Zinc is less reactive than copper.
(i) Both Assertion and Reason are true and the Reason is the correct explanation for Assertion.
(ii) Both Assertion and Reason are true and the Reason is not correct explanation for Assertion
(iii) Assertion is true but the Reason is false.
(iv) Both Assertion and Reason are false.
(v) Assertion is false but Reason is true.
Answer:

The answer is the option (iv) As Zinc is more reactive than Copper, Zinc dissolves in $CuS{O}_4$ solution.

NCERT Exemplar Class 12 Chemistry Solutions Chapter 3: Long Answer Type

Question:66

Consider the following figure and answer the following questions.

(i) Cell ‘A’ has E_cell = 2 V and cell ‘B’ has E_cell = 1.1 V which of the two cells ‘A’ or ‘B’ will act as an electrolytic cell. Which electrode reactions will occur in this cell?
(ii) If cell ‘A’ has E_cell = 0.5 V and cell ‘B’ has E_cell = 1.1 V, what will be the reactions at anode and cathode?
Answer:

(i) As the potential of ‘B’ is lower than the potential of ‘A’, it will act as the electrolytic cell. The reactions at electrode ‘B’ are shown below:
Cathode : $Z{n}^{2+}+2e^{-}\to Zn(s)$
Anode: $Cu(s)\to C{u}^{2+}+2e^{-}$
(ii) At higher potential, Cell ‘B’ acts as a galvanic cell and the reactions will be:
Anode :$Zn(s)\to Z{n}^{2+}+2e^{-}$
Cathode : $C{u}^{2+}+2e^{-}\to Cu(s)$

Question:67

Consider the figure given below and answer the questions (i) to (vi) that follow.

(i) Redraw the diagram to show the direction of electron flow.
(ii) Is silver plate anode or cathode?
(iii) What will happen if salt bridge is removed?
(iv) When will the cell stop functioning?
(v) How will concentration of $Z{n}^{+2}$ ions and $A{g}^{+}$ ions be affected when the cell functions ?
(vi) How will the concentration of $Z{n}^{+2}$ ions and $A{g}^{+}$ ions be affected after the cell becomes ‘dead’?

Answer:

(i) The cell reaction can be summarised as:
$Zn(s)\left|Z{n}^{+2}\right|\left|A{g}^{+}\right|Ag$
Electrons move from Zn to Ag.
(ii) Due to a higher standard reduction potential, Silver will act as Cathode and in the external circuit, electrons will flow from zinc anode to silver cathode.
(iii) Removal of salt bridge will lead to a sudden drop in potential to zero.
(iv) If the potential reaches zero (or the cell is discharged), all reactions will cease and the cell will stop functioning.
(v) Nernst equation for the cell is: 0.059,
$E=E^0-\frac{0.059}{2}log\frac{[Z{n}^{2+}]}{[A{g}^{+}{]}^2}$
With increase in concentration of $[Z{n}^{+2}]$, cell potential will decrease, and with an increase in concentration of $[A{g}^{+}]$, cell potential will increase.

(vi) At equilibrium (discharged state, potential drop to zero), the concentration of $[Z{n}^{+2}]$ and $[A{g}^{+}]$ will not change.

Question:68

What is the relationship between Gibbs free energy of the cell reaction in a galvanic cell and the emf of the cell? When will the maximum work be obtained from a galvanic cell?
Answer:

The required relationship between Gibbs free energy and the emf in a galvanic cell is $\mathrm{\Delta }G=-nFE$
The maximum work will be obtained from a galvanic cell $W_{max}=nF{E}^0$ where,
E=cell potential
$E^0$ = Standard emf of the cell