Electrochemistry
Multiple Choice Questions (MCQs)
1. Which cell will measure standard electrode potential of copper electrode?
(a) Pt (s)
(b) Pt (s)
(c)
(d)
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Answer
(c) Standard electrode potential of copper electrode can be calculated by constructing a concentration cell composed of two half cell reactions in which concentration of species on left hand and right hand side are unity. In such case cell potential is equal to standard electrode potential.
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Option (a): The hydrogen gas pressure is 0.1 bar instead of the standard 1 bar, which means it does not meet the standard conditions required for measuring the standard electrode potential.
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Option (b): The concentration of ( \text{Cu}^{2+} ) is 2 M instead of the standard 1 M, which means it does not meet the standard conditions required for measuring the standard electrode potential.
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Option (d): Both the hydrogen gas pressure is 0.1 bar and the concentration of ( \text{H}^+ ) is 0.1 M, neither of which meet the standard conditions required for measuring the standard electrode potential.
2. Electrode potential for
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Thinking Process
This problem includes concept of Nernst equation and its transformation to equation of straight line.
Answer
Electrode potential for Mg electrode varies according to the equation
This equation represents equation of straight line. It can be correlated as
So, intercept
Thus, equation can be diagramatically represented as
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Option 1:
- The graph in Option 1 shows a negative slope, which implies that the electrode potential decreases as the concentration of ( \text{Mg}^{2+} ) increases. However, according to the given equation ( E_{Mg^{2+} / Mg} = E_{Mg^{2+} / Mg}^{\circ} + \frac{0.059}{2} \log [Mg^{2+}] ), the slope should be positive (( \frac{0.059}{2} )), indicating that the electrode potential increases with an increase in ( \text{Mg}^{2+} ) concentration.
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Option 2:
- The graph in Option 2 shows a horizontal line, which implies that the electrode potential is constant and does not change with the concentration of ( \text{Mg}^{2+} ). This contradicts the given equation, which indicates a linear relationship between ( E_{Mg^{2+} / Mg} ) and ( \log [Mg^{2+}] ) with a positive slope.
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Option 3:
- The graph in Option 3 shows a curve, which implies a non-linear relationship between the electrode potential and the concentration of ( \text{Mg}^{2+} ). However, the given equation ( E_{Mg^{2+} / Mg} = E_{Mg^{2+} / Mg}^{\circ} + \frac{0.059}{2} \log [Mg^{2+}] ) represents a linear relationship, not a curved one. Therefore, this option is incorrect as it does not represent a straight line.
3. Which of the following statement is correct?
(a)
(b)
(c)
(d)
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Thinking Process
This problem is based on thermodynamical concept of intensive and extensive property. During answering this question must keep in mind that intensive property is independent on number of particles and extensive property is dependent on number of particles.
Answer
(c)
-
(a)
and of cell reaction both are extensive properties: This is incorrect because (cell potential) is an intensive property, meaning it does not depend on the amount of substance or the size of the system. In contrast, (Gibbs free energy change) is an extensive property, meaning it does depend on the amount of substance. -
(b)
and of cell reaction both are intensive properties: This is incorrect because while is indeed an intensive property, is an extensive property. Intensive properties do not depend on the size or amount of material in the system, whereas extensive properties do. -
(d)
is an extensive property while of cell reaction is an intensive property: This is incorrect because is an intensive property, not an extensive one. Conversely, is an extensive property, not an intensive one.
4. The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called…..
(a) cell potential
(b) cell emf
(c) potential difference
(d) cell voltage
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Answer
(b) Cell emf The difference between the electrode potential of two electrodes when no current is drawn through the cell is called cell emf.
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(a) Cell potential: This term is often used interchangeably with cell emf, but it can also refer to the potential difference under conditions where current is flowing, which is not the case in the given scenario.
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(c) Potential difference: This is a general term that refers to the difference in electric potential between two points. It does not specifically refer to the condition where no current is drawn through the cell.
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(d) Cell voltage: This term typically refers to the voltage across the cell when it is operating and current is flowing. It does not specifically describe the condition where no current is drawn through the cell.
5. Which of the following statement is not correct about an inert electrode in a cell?
(a) It does not participate in the cell reaction
(b) It provides surface either for oxidation or for reduction reaction
(c) It provides surface for conduction of electrons
(d) It provides surface for redox reaction
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Answer
(d) An inert electrode in a cell provide surface for either oxidation or for reduction reaction by conduction of electrons through its surface but does not participate in the cell reaction.
It does not provide surface for redox reaction.
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(a) It does not participate in the cell reaction: This statement is correct. An inert electrode does not participate in the chemical reaction itself; it only provides a surface for the reaction to occur.
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(b) It provides surface either for oxidation or for reduction reaction: This statement is correct. An inert electrode provides a surface for either the oxidation or reduction reaction to take place.
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(c) It provides surface for conduction of electrons: This statement is correct. An inert electrode conducts electrons, allowing the redox reactions to occur at its surface.
6. An electrochemical cell can behave like an electrolytic cell when…… .
(a)
(c)
(b)
(d)
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Answer
(c) If an external opposite potential is applied on the galvanic cell and increased reaction continues to take place till the opposing voltage reaches the value
At this stage no current flow through the cell and if there is any further increase in the external potential then reaction starts functioning in opposite direction.
Hence, this works as an electrolytic cell.
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(a) ( E_{\text{cell}} = 0 ): When the cell potential is zero, it means that the cell is at equilibrium and no net reaction occurs. This does not cause the cell to behave like an electrolytic cell, as there is no driving force for the reaction to proceed in either direction.
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(b) ( E_{\text{cell}} > E_{\text{ext}} ): In this case, the cell potential is greater than the external potential, which means the galvanic cell will continue to operate normally, driving the spontaneous reaction forward. It will not behave like an electrolytic cell because the external potential is not sufficient to reverse the reaction.
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(d) ( E_{\text{cell}} = E_{\text{ext}} ): When the cell potential is equal to the external potential, the system is in a state of equilibrium where no net current flows. This does not cause the cell to behave like an electrolytic cell, as there is no external force driving the reaction in the reverse direction.
7. Which of the statements about solutions of electrolytes is not correct?
(a) Conductivity of solution depends upon size of ions
(b) Conductivity depends upon viscosity of solution
(c) Conductivity does not depend upon solvation of ions present in solution
(d) Conductivity of solution increases with temperature
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Answer
(c) Solution consists of electrolytes is known as electrolytic solution and conductivity of electrolytic solution depends upon the following factors
(i) Size of ions As ion size increases, ion mobility decreases and conductivity decreases.
(ii) Viscosity of solution Greater the viscosity of the solvent lesser will be the conductivity of the solution.
(iii) Solvation of ions Greater the solvation of ions of an electrolyte lesser will be the electrical conductivity of the solution.
(iv) Temperature of medium Conductivity of solution increases with increase in temperature.
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(a) Conductivity of solution depends upon size of ions: This statement is correct because as the size of ions increases, their mobility decreases, leading to a decrease in conductivity.
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(b) Conductivity depends upon viscosity of solution: This statement is correct because greater viscosity of the solvent results in lower ion mobility, thereby reducing the conductivity of the solution.
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(d) Conductivity of solution increases with temperature: This statement is correct because increasing the temperature generally increases the mobility of ions, which in turn increases the conductivity of the solution.
8. Using the data given below find out the strongest reducing agent.
(a)
(b)
(c)
(d)
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Thinking Process
This problem includes concept of electrochemical series and standard reduction potential of the metal.
Higher the negative value of standard reduction potential, strongest will be the reducing agent.
As value of SRP increases from negative to positive value nature of species changes from reducing to oxidising nature.
Answer
(b) Here, out of given four options standard reduction potential of chromium has highest negative value hence most powerful reducing agent is chromium.
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(a) Cl⁻: Chloride ion (Cl⁻) has a standard reduction potential of 1.36 V for the Cl₂/Cl⁻ couple, which is a positive value. This indicates that Cl⁻ is more likely to gain electrons and be reduced rather than lose electrons and act as a reducing agent. Therefore, it is not the strongest reducing agent.
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(c) Cr³⁺: The standard reduction potential for the Cr³⁺/Cr couple is -0.74 V. While this is a negative value, indicating that Cr³⁺ can act as a reducing agent, it is not as negative as the reduction potential for Cr (which is -0.74 V for Cr³⁺/Cr). Therefore, Cr³⁺ is not the strongest reducing agent compared to Cr.
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(d) Mn²⁺: The standard reduction potential for the MnO₄⁻/Mn²⁺ couple is 1.51 V, which is a positive value. This indicates that Mn²⁺ is more likely to gain electrons and be reduced rather than lose electrons and act as a reducing agent. Therefore, it is not the strongest reducing agent.
9. Use the data given in Q. 8 and find out which of the following is the strongest oxidising agent?
(a)
(b)
(c)
(d)
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Answer
(c) Higher the positive value of standard reduction potential of metal ion higher will be its oxidising capacity.
Since,
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(a)
: The standard reduction potential of is lower than that of , indicating that is a weaker oxidising agent compared to . -
(b)
: The standard reduction potential of is lower than that of , indicating that is a weaker oxidising agent compared to . -
(d)
: The standard reduction potential of is lower than that of , indicating that is a weaker oxidising agent compared to .
10. Using the data given in 0.8 find out in which option the order of reducing power is correct.
(a)
(b)
(c)
(d)
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Answer
(b)
Species (ions) | SRP values |
---|---|
On moving top to bottom SRP value decreases from positive to negative value which will increase the reducing capacity. So, the correct option is (b).
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Option (a):
- Incorrect because
has a higher SRP value (1.51 V) than (1.36 V), so should come before in the order of reducing power.
- Incorrect because
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Option (c):
- Incorrect because
and are not included in the given SRP values table, making it impossible to determine their correct order relative to and .
- Incorrect because
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Option (d):
- Incorrect because
has a higher SRP value (1.51 V) than (1.33 V), so should come after in the order of reducing power.
- Incorrect because
11. Use the data given in Q. 8 and find out the most stable ion in its reduced form.
(a)
(b)
(c)
(d)
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Answer
(d)
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(a)
: The standard reduction potential for is +1.36 V, which is lower than the +1.51 V for . Therefore, is less stable in its reduced form compared to . -
(b)
: The standard reduction potential for is +1.33 V, which is also lower than the +1.51 V for . Hence, is less stable in its reduced form compared to . -
(c)
: The standard reduction potential for is -0.74 V, which is significantly lower than the +1.51 V for . This makes much less stable in its reduced form compared to .
12. Use the data of
(a)
(b)
(c)
(d)
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Answer
(a)
-
(b)
: The value is highly positive, indicating that is a strong oxidizing agent and not a stable oxidized species. -
(c)
: The value is also positive, suggesting that is a strong oxidizing agent and not a stable oxidized species. -
(d)
: The value is less negative than , indicating that is less stable as an oxidized species compared to .
13. The quantity of charge required to obtain one mole of aluminium from
(a)
(b)
(c)
(d)
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Answer
(c) The quantity of charge required to obtain one mole of aluminium from
Hence, total
-
Option (a)
: This is incorrect because (Faraday) corresponds to the charge required to deposit or liberate one mole of a monovalent ion. Since aluminium is trivalent ( ), it requires 3 moles of electrons (3 Faradays) to reduce one mole of to aluminium metal. -
Option (b)
: This is incorrect because it overestimates the charge required. For one mole of aluminium, only 3 Faradays are needed, as each aluminium ion requires 3 electrons for reduction. Therefore, 6 Faradays would be double the necessary amount. -
Option (d)
: This is incorrect because it underestimates the charge required. Since each ion needs 3 electrons to be reduced to aluminium metal, 2 Faradays would not be sufficient to reduce one mole of ions.
14. The cell constant of a conductivity cell…… .
(a) changes with change of electrolyte
(b) changes with change of concentration of electrolyte
(c) changes with temperature of electrolyte
(d) remains constant for a cell
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Answer
(d) Cell constant is defined as the ratio of length of object and area of cross section.
Since,
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(a) The cell constant does not change with the change of electrolyte because it is a geometric property of the cell, dependent only on the physical dimensions (length and area) of the cell, not on the type of electrolyte used.
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(b) The cell constant does not change with the change of concentration of electrolyte because it is independent of the properties of the solution. It is solely determined by the physical dimensions of the cell.
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(c) The cell constant does not change with the temperature of the electrolyte because temperature affects the conductivity of the electrolyte, not the physical dimensions of the cell. The cell constant is a fixed value based on the cell’s geometry.
15. While charging the lead storage battery…… .
(a)
(c)
(b)
(d)
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Answer
(a) While charging the lead storage battery the reaction occurring on cell is reversed and
Hence, option (a) is the correct choice
The electrode reactions are as follows
At cathode
At anode
Overall reaction
-
Option (c) is incorrect because during the charging process, the
at the cathode is reduced to , not oxidized. Oxidation would involve the loss of electrons, but in this case, the cathode gains electrons. -
Option (b) is incorrect because it states the correct process for the cathode but is listed as option (b) instead of option (a). The correct reduction reaction at the cathode is indeed
being reduced to . -
Option (d) is incorrect because during the charging process, the
at the anode is oxidized to , not . The anode reaction involves the conversion of to , which is an oxidation process.
Q.16
(a)
(b)
(c)
(d)
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Thinking Process
This question is based on the concept of Kohlrausch law and can be solved by using the concept involved in calculation of limiting molar conductivity of any salt. According to Kohlrausch law limiting molar conductivity of any salt is equal to sum of limiting molar conductivity of individual molar conductivity of cations and anions of electrolyte.
Answer
(b)
Hence, option (b) is correct choice.
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Option (a): This option is incorrect because it incorrectly includes
on both sides of the equation, which is not mathematically valid. The correct approach should involve combining the molar conductivities of different ions to form , not including it directly. -
Option (c): This option is incorrect because it incorrectly combines the molar conductivities of
, , and subtracts . This combination does not correctly account for the ions present in . Specifically, it does not correctly balance the contributions of and ions. -
Option (d): This option is incorrect because it incorrectly combines the molar conductivities of
, , and subtracts . This combination does not correctly account for the ions present in . Specifically, it does not correctly balance the contributions of and ions.
17. In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?
(a)
(b)
(c)
(d)
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Answer
(d) In case of electrolysis of aqueous
But due to lower
However, the actual reaction taking place in the concentrated solution of
This unexpected result is explained on the basis of the concept of ‘overvoltage’, i.e., water needs greater voltage for oxidation to
-
(a)
: This reaction represents the reduction of sodium ions to sodium metal, which would occur at the cathode, not the anode. The anode is where oxidation occurs. -
(b)
: Although this is an oxidation reaction that could occur at the anode, in the case of concentrated NaCl solution, the oxidation of chloride ions to chlorine gas is preferred due to the overvoltage effect. Water oxidation is kinetically slower and requires a higher voltage. -
(c)
; : This reaction represents the reduction of hydrogen ions to hydrogen gas, which would occur at the cathode, not the anode. The anode is where oxidation occurs.
Multiple Choice Questions (More Than One Options)
18. The positive value of the standard electrode potential of
(a) this redox couple is a stronger reducing agent than the
(b) this redox couple is a stronger oxidising agent than
(c)
(d)
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Answer
‘Lesser the
Since,
(i) This redox couple is a stronger oxidising agent than
(ii)
Hence, (b) and (d) are correct.
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(a) this redox couple is a stronger reducing agent than the
couple: This is incorrect because a higher standard electrode potential ( ) indicates a stronger oxidizing agent, not a stronger reducing agent. Since has a higher value than , it means is a stronger oxidizing agent, not a stronger reducing agent. -
(c)
can displace from acid: This is incorrect because for to displace from acid, would need to be a stronger reducing agent than . However, since has a higher value, it is a weaker reducing agent compared to . Therefore, cannot displace from acid.
Q.19
(a)
(b)
(c)
(a) In dilute sulphuric acid solution, hydrogen will be reduced at cathode
(b) In concentrated sulphuric acid solution, water will be oxidised at anode
(c) In dilute sulphuric acid solution, water will be oxidised at anode
(d) In dilute sulphuric acid solution,
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Answer
(a, c)
During the electrolysis of dilute sulphuric acid above given three reaction occurs each of which represents particular reaction either oxidation half cell reaction or reduction half cell reaction.
Oxidation half cell reactions occur at anode are as follows
Reaction having lower value of
Hence, oxidation of water occur preferentially reduction half cell reaction occurs at cathode
Hence, options (a) and (b) are correct.
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Option (b) is incorrect: In concentrated sulfuric acid solution, the oxidation of sulfate ions (
) to peroxodisulfate ( ) is more favorable due to its higher standard electrode potential ( ) compared to the oxidation of water ( ). Therefore, sulfate ions will be oxidized at the anode rather than water. -
Option (d) is incorrect: In dilute sulfuric acid solution, the oxidation of water to oxygen gas (
) is more favorable due to its lower standard electrode potential ( ) compared to the oxidation of sulfate ions to peroxodisulfate ( ). Therefore, water will be oxidized at the anode rather than sulfate ions being oxidized to tetrathionate ions.
Q.20
(a)
(b)
(c)
(d)
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Answer
At state of equilibrium
Hence, options (b) and (c) are the correct choices.
-
Option (a) is incorrect because (1.1) is the standard cell potential ((E_{\text{cell}}^{\circ})) and not the equilibrium constant ((K_C)). The equilibrium constant is a dimensionless quantity and cannot be directly equated to a voltage.
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Option (d) is incorrect because (\log K_C) is not equal to the standard cell potential ((E_{\text{cell}}^{\circ})). The correct relationship involves the logarithm of the equilibrium constant being proportional to the standard cell potential, as shown in the correct expressions (b) and (c).
21. Conductivity of an electrolytic solution depends on
(a) nature of electrolyte
(b) concentration of electrolyte
(c) power of AC source
(d) distance between the electrodes
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Answer
Conductivity of electrolytic solution is due to presence of mobile ions in the solution. This type of conductance is known as ionic conductance. Conductivity of these type of solutions depend upon
(i) the nature of electrolyte added
(ii) size of the ion produced and their solvatian
(iii) concentration of electrolyte
(iv) nature of solvent and its viscosity
(v) temperature
While power of source or distance between electrodes has no effect on conductivity of electrolyte solution.
Hence, options (a) and (b)are the correct choices.
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Power of AC source: The power of the AC source does not affect the conductivity of the electrolytic solution because conductivity is determined by the intrinsic properties of the solution, such as the nature and concentration of the electrolyte, and not by the external power applied.
-
Distance between the electrodes: The distance between the electrodes does not affect the conductivity of the electrolytic solution because conductivity is a property of the solution itself. While the distance between electrodes can affect the resistance measured in a specific setup, it does not change the inherent conductivity of the solution.
Q.22
(a)
(c)
(b)
(d)
Show Answer
Thinking Process
This problem includes concept of Kohlrausch law and its application in determination of molar conductivity of species. This problem can be solved by following three steps.
(i) Write the molar conductance of each species in terms of sum of their constituent ions.
(ii) Now operate the equation of each option given above by using information provided in the question.
(iii) At last if the sum of molar conductivity remaining constituent ions is equal to the molar conductivity of species asked (here
Answer
(a, c)
(a)
(d)
This type of decomposition is not possible due to weak basic strength of
(b)
(b) is incorrect
(c)
Hence, Options (a) and (c) are the correct choices.
-
Option (b) is incorrect because the expression (\Lambda_{m(HNO_3)}^{\circ} + \Lambda_{m(NaNO_3)}^{\circ} - \Lambda_{m(NaOH)}^{\circ}) simplifies to (\Lambda_{m(H^{+})}^{\circ} + 2\Lambda_{m(NO_3^{-})}^{\circ} - \Lambda_{m(OH^{-})}^{\circ}), which does not result in (\Lambda_{m(H_2O)}^{\circ}). Instead, it includes an extra term (\Lambda_{m(NO_3^{-})}^{\circ}).
-
Option (d) is incorrect because the decomposition involving (\Lambda_{m(NH_4OH)}^{\circ}) is not valid due to the weak basic strength of (NH_4OH). The expression (\Lambda_{m(NH_4OH)}^{\circ} + \Lambda_{m(HCl)}^{\circ} - \Lambda_{m(NH_4Cl)}^{\circ}) would theoretically simplify to (\Lambda_{m(H^{+})}^{\circ} + \Lambda_{m(OH^{-})}^{\circ}), but the weak basic nature of (NH_4OH) makes this decomposition impractical.
23. What will happen during the electrolysis of aqueous solution of
(a) Copper will deposit at cathode
(b) Copper will deposit at anode
(c) Oxygen will be released at anode
(d) Copper will dissolve at anode
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Thinking Process
This problem is based on electrolysis of electrolytes.
Answer
(a, c)
For electrolysis of aqueous solution of
-
(b) Copper will deposit at anode: This is incorrect because, in the electrolysis of an aqueous solution of
using platinum electrodes, the anode reaction involves the oxidation of water to produce oxygen gas, not the deposition of copper. Copper deposition occurs at the cathode. -
(d) Copper will dissolve at anode: This is incorrect because the anode reaction in this setup involves the oxidation of water to release oxygen gas. Copper dissolution at the anode would occur if the anode itself were made of copper, but in this case, platinum electrodes are used.
24. What will happen during the electrolysis of aqueous solution of
(a) Copper will deposit at cathode
(b) Copper will dissolve at anode
(c) Oxygen will be released at anode
(d) Copper will deposit at anode
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Answer
Electrolysis of
Here, Cu will deposit at cathode while copper will dissolved at anode.
Hence, options (a) and (b) are the correct choices.
-
Option (c): Oxygen will be released at anode
- This option is incorrect because in the presence of copper electrodes, the copper anode will dissolve into the solution as Cu²⁺ ions rather than releasing oxygen. The dissolution of copper at the anode is more favorable than the oxidation of water to release oxygen.
-
Option (d): Copper will deposit at anode
- This option is incorrect because at the anode, copper actually dissolves into the solution as Cu²⁺ ions. Deposition of copper occurs at the cathode, not the anode.
25. Conductivity
(a)
(b)
(c)
(d)
Show Answer
Answer
As we know that, conductance is reciprocal of resistance and conductivity is the conductance of
Hence, options (a) and (b) are the correct choices.
-
Option (c)
is incorrect because represents molar conductivity, which is different from conductivity . Molar conductivity is defined as the conductivity of an electrolyte solution divided by the molar concentration of the electrolyte, whereas conductivity is a measure of a material’s ability to conduct electric current. -
Option (d)
is incorrect because it represents the ratio of the length to the cross-sectional area of a material, which is related to the geometry of the material rather than its intrinsic property of conductivity. Conductivity is a material property and is not directly given by the ratio .
26. Molar conductivity of ionic solution depends on…… .
(a) temperature
(b) distance between electrodes
(c) concentration of electrolytes in solution
(d) surface area of electrodes
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Answer
(a, c)
Molar conductivity is the conductivity due to ions furnished by one mole of electrolyte in solution. Molar conductivity of ionic solution depends on
(i) Temperature Molar conductivity of electrolyte solution increases with increase in temperature.
(iii) Concentration of electrolytes in solution As concentration of electrolyte increases, molar conductivity decreases.
-
Distance between electrodes: The distance between electrodes affects the overall resistance of the solution but does not directly influence the molar conductivity, which is an intrinsic property of the electrolyte solution.
-
Surface area of electrodes: The surface area of electrodes can affect the current and the measured conductivity in practical setups, but it does not change the intrinsic molar conductivity of the solution itself.
27. For the given cell,
(a)
(b) Cu is cathode
(c) The cell reaction is
(d)
Show Answer
Answer
Left side of cell reaction represents oxidation half cell i.e., oxidation of
(ii)
(iii)
(iv) whole cell reaction can be written as
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Hence, options (b) and (c) both are correct choices.
-
Option (a) is incorrect because in the given cell,
is the anode where oxidation occurs, not the cathode. The cathode is where reduction occurs, and in this case, it is . -
Option (d) is incorrect because
is the species being reduced, which means it is the oxidizing agent. However, the statement is misleading as it does not clearly distinguish between the element and the ion . The correct statement should be that is the oxidizing agent.
Short Answer Type Questions
28. Can absolute electrode potential of an electrode be measured?
Show Answer
Answer
No, only the difference in potential between two electrodes can be measured. This is due to the reason that oxidation or reduction cannot occur alone. So, when we measure electrode potential of any electrode we have to take a reference electrode.
29. Can
Show Answer
Answer
No, otherwise the reaction become non-feasible.
The reaction is feasible only at
when
30. Under what condition is
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Answer
At the stage of chemical equilibrium in the cell.
31. What does the negative sign in the expression
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Answer
Greater the negative reactivity of standard reduction potential of metal greater is its reactivity. It means that
Thus, zinc electrode will be the anode of the cell and hydrogen electrode will be the cathode of the cell.
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 same or different? Explain your answer.
Show Answer
Answer
Different masses of
where,
33. Depict the galvanic cell in which the cell reaction is
Show Answer
Answer
In a galvanic cell, oxidation half reaction is written on left hand side and reduction half reaction is on right hand side. Salt bridge is represented by parallel lines
34. Value of standard electrode potential for the oxidation of
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Answer
Under the condition of electrolysis of aqueous sodium chloride, oxidation of water at anode requires over potential.
Possible oxidation half cell reactions occurring at anode are
Species having lower
35. What is electrode potential?
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Answer
The potential difference between the electrode and the electrolyte in an electrochemical cell is called electrode potential.
36. Consider the following diagram in which an electrochemical cell is coupled to an electrolytic cell. What will be the polarity of electrodes ’
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Answer
The cell drawn above represents electrochemical cell in which two different electrodes are fitted in their respective electrolytic solution and cell drawn at bottom represents electrolytic cell.
Cell representation can be represented as
Charge on electrode
Charge on electrode
37. Why is alternating current used for measuring resistance of an electrolytic solution?
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Answer
Alternating current is used in electrolysis so that concentration of ions in the solution remains constant and exact value of resistance is measured.
38. A galvanic cell has electrical potential of 1.1V. If an opposing potential of
Show Answer
Answer
When an opposing potential of
39. How will the
Show Answer
Answer
The
Chemical reaction occurring at cell when aqueous brine solution is electrolysed are as follows
40. Unlike dry cell, the mercury cell has a constant cell potential throughout its useful life. Why?
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Answer
Life time of any cell depends upon ions present in cell. lons are not involved in the overall cell reaction of mercury cell. Hence, mercury cell has a constant cell potential throughout its useful life.
41. Solutions of two electrolytes
Show Answer
Answer
Strong electrolytes dissociate almost completely even on high concentration. Therefore, concentration of such solutions remain almost same on dilution. Electrolyte ’
Therefore,
42. When acidulated water (dil.
Show Answer
Answer
Since
43. In an aqueous solution how does specific conductivity of electrolytes change with addition of water?
Show Answer
Answer
Conductivity of solution due to total ions present in per unit volume of solution is known as specific conductivity. Specific conductivity decreases due to decrease in the number of ions per unit volume. We add water to aqueous solution, number of ions present in per unit volume decreases.
44. Which reference electrode is used to measure the electrode potential of other electrodes?
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Answer
Standard hydrogen electrode (SHE) is the reference electrode whose electrode potential is taken to be zero. The electrode potential of other electrodes are measured with respect to it .
45. Consider a cell given below
Write the reactions that occur at anode and cathode.
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Answer
Cell reaction represented in the question is composed of two half cell reactions. These reactions are as follows
Copper is getting oxidised at anode.
46. Write the Nernst equation for the cell reaction in the Daniel cell. How will the
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Answer
According to this equation
47. What advantage do the fuel cells have over primary and secondary batteries?
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Answer
Primary batteries contain a limited amount of reactants and are discharged when the reactants have been consumed. Secondary batteries can be recharged but it take a long time. Fuel cell run continuously as long as the reactants are supplied to it and products are removed continuously.
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?
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Answer
When a lead storage battery is discharged then the following cell reaction takes place
Density of electrolyte depends upon number. of constituent ions present in per unit volume of electrolyte solution. In this case density of electrolyte decreases as water is formed and sulphuric acid is consumed as the product during discharge of the battery.
49. Why on dilution the
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Answer
In the case of
In case of strong electrolyte, the number of ions remains the same but the interionic attraction decreases.
Matching The Columns
50. Match the terms given in Column I with the units given in Column II.
Column I | Column II | ||
---|---|---|---|
A. | 1. | ||
B. | 2. | ||
C. | 3. | ||
D. | 4. |
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Answer
A.
B.
C.
D.
Column I | Column II (Unit of parameter) | |
---|---|---|
A. | ||
B. | ||
C. | ||
D. |
51. Match the terms given in Column I with the items given in Column II.
Column I | Column II | ||
---|---|---|---|
A. | 1. | Intensive property | |
B. | 2. | Depends on number of < ions/volume | |
C. | 3. | Extensive property | |
D. | 4. | Increases with dilution |
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Answer
A.
B.
C.
D.
A.
B.
C.
D.
52. Match the items of Column I and Column II.
Column I | Column II | ||
---|---|---|---|
A. | Lead storage battery | 1. | Maximum efficiency |
B. | Mercury cell | 2. | Prevented by galvanisation |
C. | Fuel cell | 3. | Gives steady potential |
D. | Rusting | 4. |
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Answer
A.
B.
C.
D.
A. Chemical reaction occurring on lead storage battery can be represented as
At anode
At cathode
Thus,
B. Mercury cell does not include ions during their function hence produce steady current.
C. Fuel cell has maximum efficiency as they produce energy due to combustion reaction of fuel.
D. Rusting is prevented by corrosion.
53. Match the items of Column I and Column II.
Column I | Column II | ||
---|---|---|---|
A. | 1. | ||
B. | 2. | ||
C. | 3. | ||
D. | 4. |
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Answer
A.
B.
C.
D.
A. Conductivity
B. Molar conductivity
C. Degree of dissociation
D. Charge
where,
54. Match the items of Column I and Column II.
Column I | Column II | ||
---|---|---|---|
A. | Lechlanche cell | 1. | Cell reaction |
B. | 2. | Does not involve any ion in solution and is used in hearing aids. | |
C. | Fuel cell | 3. | Rechargeable |
D. | Mercury cell | 4. | Reaction at anode, |
5. Converts energy of combustion into electrical energy |
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Answer
A.
B).
C.
D.
A. Lechlanche cell The electrode reaction occurs at Lechlanche cell are
At cathode
B. Ni-Cd cell is rechargeable. So, it has more life time.
C. Fuel cell produces energy due to combustion. So, fuel cell converts energy of combustion into electrical energy e.g.,
D. Mercury cell does not involve any ion in solution and is used in hearing aids.
55. Match the items of Column I and Column II on the basis of data given below
Column I | Column II | ||
---|---|---|---|
A. | 1. | Metal is the strongest reducing agent | |
B. | 2. | Metal ion which is the weakest oxidising agent | |
C. | 3. | Non-metal which is the best oxidising agent | |
D. | 4. | Unreactive metal | |
E. | 5. | Anion that can be oxidised by |
|
F. | 6. | Anion which is the weakest reducing agent | |
G. | 7. | Metal ion which is an oxidising agent |
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Answer
A.
B.
C.
D.
E.
F.
G.
A.
B.
C.
D.
E. Au is an unreactive metal.
F.
G.
Assertion and Reason
In the following questions a statement of assertion (A) followed by a statement of reason (
(a) Both assertion and reason are true and the reason is the correct explanation of assertion.
(b) Both assertion and reason are true and reason is not the correct explanation of assertion.
(c) Assertion is true but the reason is false.
(d) Both assertion and reason are false.
(e) Assertion is false but reason is true.
56. Assertion (A)
Reason (R)
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Answer
(c) Assertion is true but the reason is false. Electrode potential of
Hence, correct reason is due to positive value of
57. Assertion (A)
Reason (R)
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Answer
(c) Assertion is true but the reason is false. Feasibility of chemical reaction depends on Gibbs free energy which is related to
When value of
Correct reason is
58. Assertion (A) Conductivity of all electrolytes decreases on dilution.
Reason (R) On dilution number of ions per unit volume decreases.
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Answer
(a) Both assertion and reason are correct and reason is the correct explanation of assertion. Since, conductivity depends upon number of ions per unit volume. Therefore, the conductivity of all electrolytes decreases on dilution due to decrease in number of ions per unit volume.
59. Assertion (A)
Reason (R) For weak electrolytes degree of dissociation increases with dilution of solution.
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Answer
(a) Assertion and reason are true and the reason is the correct explanation of the assertion.
Molar conductivity of weak electrolytic solution increases on dilution, because as we add excess water to increase the dilution degree of dissociation increases which lead to increase in number of ions in the solution. Thus,
60. Assertion (A) Mercury cell does not give steady potential. Reason (R) In the cell reaction, ions are not involved in solution.
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Answer
(e) Assertion is false but reason is true. Correct assertion is mercury cell gives steady potential.
Reason is correct as ions are not involved in cell reaction.
61. Assertion (A) Electrolysis of
Reason (R) Formation of oxygen at anode requires over voltage.
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Answer
(a) Both assertion and reason are correct and reason is the correct explanation of assertion.
Explanation Electrolysis of
62. Assertion (A) For measuring resistance of an ionic solution an
Reason (R) Concentration of ionic solution will change if DC source is used.
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Answer
(a) Both assertion and reason are correct and reason is the correct explanation of assertion
Concentration of ionic solution changes on using DC current as a source of energy while on passing AC current concentration does not change. Hence, AC source is used for measuring resistance
63. Assertion (A) Current stops flowing when
Reason (R) Equilibrium of the cell reaction is attained.
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Answer
(a) Both assertion and reason are correct and reason is the correct explanation of assertion.
Current stop flowing when
As at
64. Assertion (A)
Reason(
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Answer
(b) Both assertion and reason are correct but reason is not the correct explanation of assertion.
Thus,
65. Assertion (A) Copper sulphate can be stored in zinc vessel.
Reason (R) Zinc is less reactive than copper.
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Answer
(d) Both assertion and reason are false.
Copper sulphate can’t be stored in zinc vessel as zinc is more reactive than copper due to negative value of standard reduction potential of
Long Answer Type Questions
66. Consider the figure and answer the following questions.
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(i) Cell ’
(ii) If cell ’
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Thinking Process
This problem includes concept of electrochemical cell, electrolytic cell and charge on electrode. To solve this problem identify the charge on each electrode first.
Answer
(i) Cell ’
The electrode reactions will be
At cathode
At anode
(ii) If cell ’
Now it will push electrons into cell ’
In this case, the reactions will be
67. Consider figure from the above question and answer the questions (i) to (vi) given below.

(i) Redraw the diagram to show the direction of electron flow.
(ii) Is silver plate the anode or cathode?
(iii) What will happen if salt bridge is removed?
(iv) When will the cell stop functioning?
(v) How will concentration of
(vi) How will the concentration of
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Answer
(i) Electrons move from

(ii)
(iii) Cell will stop functioning because cell potential drops to zero. At
(v) Concentration of
(vi) When
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?
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Answer
If concentration of all reacting species is unity, then
If we want to obtain maximum work from a galvanic cell then charge has to be passed reversibly.
The reversibly work done by a galvanic cell is equal to decrease in its Gibbs energy.
As
For reaction,