Assertion A: The conductivity of an electrolyte solution falls on dilution. Reason R: The molar conductivity of an electrolyte rises on dilution. Choose the correct answer.

Both A and R are correct but R is not the correct explanation of A

A is not correct but R is correct

A is correct but R is not correct

Both A and R are correct and R is the correct explanation of A

Electrochemistry

32 NEET-UG practice questions on Electrochemistry, part of Chemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Silver and copper voltameters are connected in series. If 2.16 g of Ag is deposited from Ag⁺, what mass of Cu is deposited from Cu²⁺? (Ag = 108, Cu = 63.5 g/mol.)
1. A0.635 g
2. B1.27 g
3. C0.318 g
4. D3.67 g
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Answer: A · 0.635 g
Ag deposited = 2.16/108 = 0.020 mol, so charge = 0.020 mol e⁻. Cu²⁺ needs 2 e⁻, so Cu = 0.010 mol = 0.635 g. Check by equivalents: 2.16/108 = m/31.75 gives m = 0.635 g.
- B: Takes one mole of Cu per mole of electrons, ignoring the 2+ charge.
- C: Divides by the charge of 2 twice.
- D: Inverts the ratio of molar masses.
Remember this
In series the same charge passes, so masses deposited are in the ratio of molar mass divided by ion charge.
Question 2 · Medium
A cell reaction involving two electrons has E°cell = 0.295 V at 298 K. What is the equilibrium constant of the reaction? (Take 2.303RT/F = 0.059 V.)
1. A10²⁰
2. B10¹⁰
3. C10⁵
4. D10⁻¹⁰
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Answer: B · 10¹⁰
log K = nE°/0.059 = (2 × 0.295)/0.059 = 10, so K = 10¹⁰. Check: ΔG° = −2 × 96500 × 0.295 ≈ −56.9 kJ/mol, and 56900/(2.303 × 8.314 × 298) ≈ 10.
- A: Applies the factor n = 2 twice.
- C: Leaves out n in the expression for log K.
- D: Takes the wrong sign; a positive E° gives K above 1.
Remember this
A positive E° means negative ΔG° and K above 1, linked by ΔG° = −nFE° = −RT ln K.
Question 3 · Medium
Using the data E°(Mg²⁺/Mg) = −2.37 V, E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = −0.76 V and E°(Ag⁺/Ag) = +0.80 V, arrange the metals in increasing order of reducing power. A. Mg B. Cu C. Zn D. Ag
1. AB, D, C, A
2. BA, C, B, D
3. CD, C, B, A
4. DD, B, C, A
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Answer: D · D, B, C, A
A more negative reduction potential means the metal gives up electrons more readily and is a stronger reducing agent. Going from +0.80 V to −2.37 V gives Ag, Cu, Zn, Mg.
- A: Places copper below silver, though its E° is the lower.
- B: Gives the decreasing order, the reverse of what is asked.
- C: Places zinc below copper, ignoring the sign of its potential.
Remember this
Lower E° means stronger reducing agent; the metal with the most negative value reduces the ions of the others.
Question 4 · Easy
Given E°(Zn²⁺/Zn) = −0.76 V and E°(Ag⁺/Ag) = +0.80 V, what is the standard EMF of the cell Zn | Zn²⁺ || Ag⁺ | Ag?
1. A1.56 V
2. B0.04 V
3. C−1.56 V
4. D2.36 V
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Answer: A · 1.56 V
E°cell = E°cathode − E°anode = 0.80 − (−0.76) = 1.56 V. Silver is reduced at the cathode and zinc is oxidised at the anode.
- B: Adds the two values with their signs instead of subtracting.
- C: Subtracts in the wrong order, cathode from anode.
- D: Doubles the silver potential because two Ag⁺ appear in the equation.
Remember this
E° is intensive, so never multiply it by the coefficients in the balanced equation.
Question 5 · Medium
Assertion A: The conductivity of an electrolyte solution falls on dilution. Reason R: The molar conductivity of an electrolyte rises on dilution. Choose the correct answer.
1. AA is not correct but R is correct
2. BA is correct but R is not correct
3. CBoth A and R are correct but R is not the correct explanation of A
4. DBoth A and R are correct and R is the correct explanation of A
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Answer: C · Both A and R are correct but R is not the correct explanation of A
Conductivity depends on the ions per unit volume, which fall on dilution, so A is true. Molar conductivity rises because the volume holding one mole of electrolyte increases, so R is true. R is a separate trend and does not explain A.
- A: A is true; conductivity does fall on dilution.
- B: R is true; molar conductivity does rise on dilution.
- D: R is true but only states a companion trend; the fall in ions per volume explains A.
Remember this
κ falls with dilution from fewer ions per cm³; Λm = κ/c rises because c falls faster.
Question 6 · Easy
In a lead storage battery during discharge, which substance is oxidised at the anode?
1. APb
2. BH₂SO₄
3. CPbSO₄
4. DPbO₂
Answer and explanation in LearnFree account
Question 7 · Medium
For the cell Zn | Zn²⁺ (0.1 M) || Cu²⁺ (0.001 M) | Cu at 298 K, E°cell = 1.10 V. Calculate E_cell. (Take 2.303RT/F = 0.059 V.)
1. A0.982 V
2. B1.041 V
3. C1.159 V
4. D1.100 V
Answer and explanation in LearnFree account
Question 8 · Hard
At 298 K the limiting molar conductivities (in S cm² mol⁻¹) are HCl = 425, KCl = 150 and KX = 120. A 0.02 M solution of the weak acid HX has a molar conductivity of 79 S cm² mol⁻¹. What is the K_a of HX?
1. A8.0 × 10⁻⁴
2. B4.0 × 10⁻³
3. C1.0 × 10⁻³
4. D2.9 × 10⁻⁴
Answer and explanation in LearnFree account
Question 9 · Easy
The figure plots molar conductivity against √c for two electrolytes in water. Given below are two statements: Statement I: Curve I can be extrapolated to zero concentration to obtain the limiting molar conductivity, but curve II cannot. Statement II: Curve II is the type of curve obtained for KCl. Choose the correct answer.
Figure: MedExams
1. ABoth Statement I and Statement II are correct
2. BStatement I is correct but Statement II is incorrect
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are incorrect
Answer and explanation in LearnFree account
Question 10 · Hard
The three cells in the figure carry the same charge, and each metal ion is reduced at its cathode with 100% efficiency. While 3.24 g of silver deposits in Cell I, what masses deposit in Cell II and Cell III? (Atomic masses: Ag = 108, Cu = 63.5, Au = 197)
Figure: MedExams
1. ACu 0.95 g, Au 5.91 g
2. BCu 0.95 g, Au 1.97 g
3. CCu 1.91 g, Au 5.91 g
4. DCu 1.91 g, Au 1.97 g
Answer and explanation in LearnFree account
Question 11 · Medium
A cell at 298 K follows the line shown, with E°cell at log₁₀ Q = 0. Taking 2.303RT/F = 0.06 V and F = 96500 C mol⁻¹, find ΔG° for the cell reaction as written.
Figure: MedExams
1. A+212.3 kJ mol⁻¹
2. B−106.2 kJ mol⁻¹
3. C−424.6 kJ mol⁻¹
4. D−212.3 kJ mol⁻¹
Answer and explanation in LearnFree account
Question 12 · Easy
A solution of an electrolyte of concentration 0.10 mol L⁻¹ has a conductivity of 1.2 × 10⁻² S cm⁻¹. What is its molar conductivity?
1. A1.2 S cm² mol⁻¹
2. B12 S cm² mol⁻¹
3. C0.12 S cm² mol⁻¹
4. D120 S cm² mol⁻¹
Answer and explanation in LearnFree account
Question 13 · Hard
Consider the cell at 298 K: Ag | Ag⁺(0.001 M) || Ag⁺(0.1 M) | Ag Taking 2.303RT/F = 0.059 V, which option gives the EMF of the cell and identifies its anode?
1. A0.059 V; the silver rod in 0.001 M Ag⁺ is the anode
2. B0.118 V; the silver rod in 0.1 M Ag⁺ is the anode
3. C0 V; no current flows because E°cell is zero
4. D0.118 V; the silver rod in 0.001 M Ag⁺ is the anode
Answer and explanation in LearnFree account
Question 14 · Medium
Water is electrolysed with a steady current of 2.0 A. How long will it take to liberate 1.12 L of oxygen measured at STP? (Molar volume at STP = 22.4 L; F = 96500 C mol⁻¹)
1. A9650 s
2. B19300 s
3. C4825 s
4. D2412.5 s
Answer and explanation in LearnFree account
Question 15 · Medium
Limiting molar conductivities at 298 K (in S cm² mol⁻¹) are: HCl 426, CH₃COOK 114 and KCl 150. A certain acetic acid solution has a molar conductivity of 19.5 S cm² mol⁻¹. Find the degree of dissociation of acetic acid in it.
1. A0.028
2. B0.042
3. C0.050
4. D0.12
Answer and explanation in LearnFree account
Question 16 · Medium
Given below are two statements: Statement I: When a KCl solution is diluted, its conductivity decreases but its molar conductivity increases. Statement II: For a strong electrolyte, a plot of molar conductivity against √c is a straight line with a negative slope. Choose the correct answer.
1. AStatement I is incorrect but Statement II is correct
2. BStatement I is correct but Statement II is incorrect
3. CBoth Statement I and Statement II are correct
4. DBoth Statement I and Statement II are incorrect
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Question 17 · Hard
Consider the cell Cu(s) | Cu²⁺(1.0 M) || Ag⁺(x M) | Ag(s) at 298 K, with E°(Cu²⁺/Cu) = +0.34 V and E°(Ag⁺/Ag) = +0.80 V. The measured EMF is 0.40 V. Taking 2.303RT/F = 0.06 V, find x.
1. A10
2. B0.1
3. C0.32
4. D0.01
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Question 18 · Medium
Given below are two statements: Statement I: When aqueous sodium chloride is electrolysed with platinum electrodes, sodium metal is deposited at the cathode. Statement II: When molten sodium chloride is electrolysed, sodium is formed at the cathode and chlorine at the anode. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is incorrect but Statement II is correct
3. CStatement I is correct but Statement II is incorrect
4. DBoth Statement I and Statement II are incorrect
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Question 19 · Easy
How many faradays of electricity are needed to reduce one mole of MnO₄⁻ ions to Mn²⁺ ions?
1. A3 F
2. B2 F
3. C7 F
4. D5 F
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Question 20 · Medium
A hydrogen electrode, with hydrogen gas at 1 bar, dips into a solution of pH 3 at 298 K. Taking 2.303RT/F = 0.059 V, what is its reduction potential?
1. A−0.059 V
2. B−0.177 V
3. C−0.0885 V
4. D+0.177 V
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Question 21 · Medium
Limiting molar conductivities of two ions at 298 K are λ°(Al³⁺) = 189 S cm² mol⁻¹ and λ°(SO₄²⁻) = 160 S cm² mol⁻¹. Using Kohlrausch's law, what is the limiting molar conductivity of Al₂(SO₄)₃?
1. A538 S cm² mol⁻¹
2. B887 S cm² mol⁻¹
3. C349 S cm² mol⁻¹
4. D858 S cm² mol⁻¹
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Question 22 · Hard
Using E°(Fe²⁺/Fe) = −0.44 V and E°(Fe³⁺/Fe²⁺) = +0.77 V, calculate the standard reduction potential of the Fe³⁺/Fe couple.
1. A−0.11 V
2. B−0.037 V
3. C+0.33 V
4. D+0.165 V
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Question 23 · Hard
Taking E°(Mg²⁺/Mg) = −2.37 V, E°(Cu²⁺/Cu) = +0.34 V and 2.303RT/F = 0.059 V, what is the EMF at 298 K of the cell Mg | Mg²⁺(0.01 M) || Cu²⁺(0.10 M) | Cu?
1. A2.03 V
2. B2.77 V
3. C2.68 V
4. D2.74 V
Answer and explanation in LearnFree account
Question 24 · Medium
A zinc rod dips into 0.01 M ZnSO₄ solution at 298 K. Using E°(Zn²⁺/Zn) = −0.76 V and 2.303RT/F = 0.059 V, find its reduction potential.
1. A−0.701 V
2. B−0.819 V
3. C−0.760 V
4. D−0.878 V
Answer and explanation in LearnFree account
Question 25 · Easy
What is the SI unit of conductivity (κ) of an electrolytic solution?
1. AS m² mol⁻¹
2. BS m⁻¹
3. CΩ m
4. DS m
Answer and explanation in LearnFree account

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Electrochemistry

Silver and copper voltameters are connected in series. If 2.16 g of Ag is deposited from Ag⁺, what mass of Cu is deposited from Cu²⁺? (Ag = 108, Cu = 63.5 g/mol.)

A cell reaction involving two electrons has E°cell = 0.295 V at 298 K. What is the equilibrium constant of the reaction? (Take 2.303RT/F = 0.059 V.)

Using the data E°(Mg²⁺/Mg) = −2.37 V, E°(Cu²⁺/Cu) = +0.34 V, E°(Zn²⁺/Zn) = −0.76 V and E°(Ag⁺/Ag) = +0.80 V, arrange the metals in increasing order of reducing power. A. Mg B. Cu C. Zn D. Ag

Given E°(Zn²⁺/Zn) = −0.76 V and E°(Ag⁺/Ag) = +0.80 V, what is the standard EMF of the cell Zn | Zn²⁺ || Ag⁺ | Ag?

Assertion A: The conductivity of an electrolyte solution falls on dilution. Reason R: The molar conductivity of an electrolyte rises on dilution. Choose the correct answer.

In a lead storage battery during discharge, which substance is oxidised at the anode?

For the cell Zn | Zn²⁺ (0.1 M) || Cu²⁺ (0.001 M) | Cu at 298 K, E°cell = 1.10 V. Calculate E_cell. (Take 2.303RT/F = 0.059 V.)

At 298 K the limiting molar conductivities (in S cm² mol⁻¹) are HCl = 425, KCl = 150 and KX = 120. A 0.02 M solution of the weak acid HX has a molar conductivity of 79 S cm² mol⁻¹. What is the K_a of HX?

The three cells in the figure carry the same charge, and each metal ion is reduced at its cathode with 100% efficiency. While 3.24 g of silver deposits in Cell I, what masses deposit in Cell II and Cell III? (Atomic masses: Ag = 108, Cu = 63.5, Au = 197)

A cell at 298 K follows the line shown, with E°cell at log₁₀ Q = 0. Taking 2.303RT/F = 0.06 V and F = 96500 C mol⁻¹, find ΔG° for the cell reaction as written.

A solution of an electrolyte of concentration 0.10 mol L⁻¹ has a conductivity of 1.2 × 10⁻² S cm⁻¹. What is its molar conductivity?

Consider the cell at 298 K: Ag | Ag⁺(0.001 M) || Ag⁺(0.1 M) | Ag Taking 2.303RT/F = 0.059 V, which option gives the EMF of the cell and identifies its anode?

Water is electrolysed with a steady current of 2.0 A. How long will it take to liberate 1.12 L of oxygen measured at STP? (Molar volume at STP = 22.4 L; F = 96500 C mol⁻¹)

Limiting molar conductivities at 298 K (in S cm² mol⁻¹) are: HCl 426, CH₃COOK 114 and KCl 150. A certain acetic acid solution has a molar conductivity of 19.5 S cm² mol⁻¹. Find the degree of dissociation of acetic acid in it.

Given below are two statements: Statement I: When a KCl solution is diluted, its conductivity decreases but its molar conductivity increases. Statement II: For a strong electrolyte, a plot of molar conductivity against √c is a straight line with a negative slope. Choose the correct answer.

Consider the cell Cu(s) | Cu²⁺(1.0 M) || Ag⁺(x M) | Ag(s) at 298 K, with E°(Cu²⁺/Cu) = +0.34 V and E°(Ag⁺/Ag) = +0.80 V. The measured EMF is 0.40 V. Taking 2.303RT/F = 0.06 V, find x.

How many faradays of electricity are needed to reduce one mole of MnO₄⁻ ions to Mn²⁺ ions?

A hydrogen electrode, with hydrogen gas at 1 bar, dips into a solution of pH 3 at 298 K. Taking 2.303RT/F = 0.059 V, what is its reduction potential?

Limiting molar conductivities of two ions at 298 K are λ°(Al³⁺) = 189 S cm² mol⁻¹ and λ°(SO₄²⁻) = 160 S cm² mol⁻¹. Using Kohlrausch's law, what is the limiting molar conductivity of Al₂(SO₄)₃?

Using E°(Fe²⁺/Fe) = −0.44 V and E°(Fe³⁺/Fe²⁺) = +0.77 V, calculate the standard reduction potential of the Fe³⁺/Fe couple.

Taking E°(Mg²⁺/Mg) = −2.37 V, E°(Cu²⁺/Cu) = +0.34 V and 2.303RT/F = 0.059 V, what is the EMF at 298 K of the cell Mg | Mg²⁺(0.01 M) || Cu²⁺(0.10 M) | Cu?

A zinc rod dips into 0.01 M ZnSO₄ solution at 298 K. Using E°(Zn²⁺/Zn) = −0.76 V and 2.303RT/F = 0.059 V, find its reduction potential.

What is the SI unit of conductivity (κ) of an electrolytic solution?