JEE Chemistry Electrochemistry MCQs Set 21

Practice MCQs for JEE Chemistry Electrochemistry

Review structured MCQ sets for JEE Chemistry Electrochemistry. Built according to official JEE guidelines, these downloadable questions support daily revision and core concept reinforcement.

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Multiple Choice Questions

Question 1: Strong electrolytes are those which:
(a) dissolve readily in water
(b) conduct electricity
(c) dissociate into ions even at high concentration
(d) dissociate into ions at high dilution only
Show Answer & Explanation

Answer: (c) dissociate into ions even at high concentration

Explanation:
1. A strong electrolyte is almost completely ionised at all concentrations.
2. Solubility and the ability to conduct do not define strength.
3. Answer: (c)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 2: Molten sodium chloride conducts electricity due to the presence of:
(a) free electrons
(b) free ions
(c) free molecules
(d) free atoms of Na and Cl
Show Answer & Explanation

Answer: (b) free ions

Explanation:
1. Melting frees Na+ and Cl− ions from the lattice; their movement carries current.
2. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 3: Electrolytic conduction is due to the movement of:
(a) molecules
(b) atoms
(c) ions
(d) electrons
Show Answer & Explanation

Answer: (c) ions

Explanation:
1. In electrolytes, charge is carried by ions, unlike metals where electrons carry it.
2. Answer: (c)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 4: Which of the following solutions of KCl has the lowest value of equivalent conductance?
(a) 1 M
(b) 0.1 M
(c) 0.01 M
(d) 0.001 M
Show Answer & Explanation

Answer: (a) 1 M

Explanation:
1. Equivalent conductance rises on dilution because inter-ionic attraction falls.
2. The most concentrated solution (1 M) has the lowest value.
3. Answer: (a)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 5: In the equation Λ = specific conductance × V, V is the volume in cc containing 1 equivalent of the electrolyte. V for an N/10 solution will be:
(a) 10 cc
(b) 100 cc
(c) 1000 cc
(d) 10,000 cc
Show Answer & Explanation

Answer: (d) 10,000 cc

Explanation:
1. N/10 means 0.1 equivalent per litre, so 1 equivalent is in 10 L = 10,000 cc.
2. Answer: (d)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 6: The specific conductances in ohm−1 cm−1 of four electrolytes P, Q, R and S are: P (5.0 × 10−5), Q (7.0 × 10−8), R (1.0 × 10−10), S (9.2 × 10−3). The one that offers the highest resistance to the passage of electric current is:
(a) P
(b) S
(c) R
(d) Q
Show Answer & Explanation

Answer: (c) R

Explanation:
1. Resistance is inversely related to conductance.
2. R has the smallest specific conductance (10−10), so it has the highest resistance.
3. Answer: (c)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 7: The molar conductivity of HCl is greater than that of NaCl at a particular temperature because:
(a) The molecular mass of HCl is less than that of NaCl
(b) The velocity of H+ ions is more than that of Na+ ions
(c) HCl is strongly acidic
(d) Ionisation of HCl is larger than that of NaCl
Show Answer & Explanation

Answer: (b) The velocity of H+ ions is more than that of Na+ ions

Explanation:
1. Both are strong electrolytes and fully ionised.
2. H+ has a very high ionic mobility (proton transfer through water), so λ(H+) is much more than λ(Na+).
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 8: Which statement is NOT correct?
(a) Equivalent conductance of an electrolytic solution increases with dilution
(b) Equivalent conductance of an electrolytic solution decreases with dilution
(c) Specific conductance of an electrolytic solution decreases with dilution
(d) Molar conductance of an electrolytic solution increases with dilution
Show Answer & Explanation

Answer: (b) Equivalent conductance of an electrolytic solution decreases with dilution

Explanation:
1. On dilution the number of ions per unit volume falls, so specific conductance (κ) decreases.
2. But ionisation increases and inter-ionic attraction decreases, so equivalent and molar conductance increase.
3. Hence statement (b) is incorrect.
4. Answer: (b)

Teacher's Note:
1. Λ rises on dilution while κ falls.
2. Λ = 1000κ/C: C falls faster than κ.

Question 9: The resistance of a 0.01 N solution of an electrolyte was found to be 210 ohm at 298 K using a conductivity cell of cell constant 0.66 cm−1. The equivalent conductance of the solution is:
(a) 314.28 mho cm2 eq−1
(b) 3.14 mho cm2 eq−1
(c) 314.28 mho−1 cm2 eq−1
(d) 3.14 mho−1 cm2 eq−1
Show Answer & Explanation

Answer: (a) 314.28 mho cm2 eq−1

Explanation:
1. κ = cell constant/R = 0.66/210 = 3.143 × 10−3 mho cm−1.
2. Λeq = 1000κ/N = 1000 × 3.143 × 10−3/0.01 = 314.3 mho cm2 eq−1.
3. Answer: (a)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 10: Electrolytic conduction differs from metallic conduction in that in the former:
(a) The resistance increases with increasing temperature
(b) The resistance decreases with increasing temperature
(c) The resistance remains constant with increasing temperature
(d) The resistance is independent of the length of the conductor
Show Answer & Explanation

Answer: (b) The resistance decreases with increasing temperature

Explanation:
1. Higher temperature lowers viscosity and increases ionisation and ion mobility, so the resistance of an electrolyte falls.
2. Metals show the opposite trend.
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 11: At infinite dilution, the equivalent conductances of CH3COONa, HCl and CH3COOH are 91, 426 and 391 mho cm2 eq−1 respectively at 25°C. The equivalent conductance of NaCl at infinite dilution will be:
(a) 126
(b) 209
(c) 391
(d) 908
Show Answer & Explanation

Answer: (a) 126

Explanation:
1. Kohlrausch's law: Λ0(NaCl) = Λ0(CH3COONa) + Λ0(HCl) − Λ0(CH3COOH).
2. = 91 + 426 − 391 = 126.
3. Answer: (a)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 12: The equivalent conductivity of 0.1 N CH3COOH at 25°C is 80 and at infinite dilution it is 400. The degree of dissociation of CH3COOH is:
(a) 1
(b) 0.2
(c) 0.1
(d) 0.5
Show Answer & Explanation

Answer: (b) 0.2

Explanation:
1. α = Λc/Λ0 = 80/400 = 0.2.
2. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 13: The molar conductivities Λ0NaOAc and Λ0HCl at infinite dilution in water at 25°C are 91.0 and 426.2 S cm2 mol−1 respectively. To calculate Λ0HOAc, the additional value required is:
(a) Λ0NaCl
(b) Λ0H2O
(c) Λ0KCl
(d) Λ0NaOH
Show Answer & Explanation

Answer: (a) Λ0NaCl

Explanation:
1. Λ0(HOAc) = Λ0(NaOAc) + Λ0(HCl) − Λ0(NaCl).
2. So Λ0(NaCl) is needed.
3. Answer: (a)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 14: The conductivity of a saturated solution of BaSO4 is 3.06 × 10−6 ohm−1 cm−1 and its molar conductance is 1.53 ohm−1 cm2 mol−1. The Ksp of BaSO4 will be:
(a) 4 × 10−12
(b) 2.5 × 10−9
(c) 2.5 × 10−13
(d) 4 × 10−6
Show Answer & Explanation

Answer: (d) 4 × 10−6

Explanation:
1. Solubility S = 1000κ/Λm = 1000 × 3.06 × 10−6/1.53 = 2 × 10−3 mol L−1.
2. Ksp = S2 = 4 × 10−6 (with the data as given).
3. Answer: (d)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 15: In the galvanic cell Cu | Cu2+ (1 M) || Ag+ (1 M) | Ag, the electrons will travel in the external circuit:
(a) from Ag to Cu
(b) from Cu to Ag
(c) electrons do not travel in the external circuit
(d) in any direction
Show Answer & Explanation

Answer: (b) from Cu to Ag

Explanation:
1. Cu is oxidised at the anode (Cu → Cu2+ + 2e−) and Ag+ is reduced at the cathode.
2. Electrons flow from Cu to Ag.
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 16: The passage of electricity in the Daniell cell when Zn and Cu electrodes are connected is:
(a) from Cu to Zn in the cell
(b) from Cu to Zn outside the cell
(c) from Zn to Cu outside the cell
(d) in any direction in the cell
Show Answer & Explanation

Answer: (b) from Cu to Zn outside the cell

Explanation:
1. Electrons leave Zn (anode) and travel to Cu through the wire.
2. Conventional current is opposite to electron flow, so it flows from Cu to Zn outside the cell.
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 17: The equation representing the process by which the standard reduction potential of zinc can be defined is:
(a) Zn2+(s) + 2e− → Zn
(b) Zn(g) → Zn2+(g) + 2e−
(c) Zn2+(g) + 2e− → Zn
(d) Zn2+(aq) + 2e− → Zn(s)
Show Answer & Explanation

Answer: (d) Zn2+(aq) + 2e− → Zn(s)

Explanation:
1. Standard reduction potential refers to Zn2+(aq, 1 M) + 2e− → Zn(s).
2. Answer: (d)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 18: A standard hydrogen electrode has zero electrode potential because:
(a) Hydrogen is easiest to oxidise
(b) This electrode potential is assumed to be zero
(c) Hydrogen atom has only one electron
(d) Hydrogen is the lightest element
Show Answer & Explanation

Answer: (b) This electrode potential is assumed to be zero

Explanation:
1. Absolute single-electrode potentials cannot be measured.
2. By convention the SHE is assigned 0.00 V as the reference.
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 19: Which is NOT true for a standard hydrogen electrode?
(a) The hydrogen ion concentration is 1 M
(b) The temperature is 25°C
(c) The pressure of hydrogen is 1 bar
(d) It contains a metallic conductor which does not adsorb hydrogen
Show Answer & Explanation

Answer: (d) It contains a metallic conductor which does not adsorb hydrogen

Explanation:
1. The SHE uses platinised platinum (platinum black), which adsorbs hydrogen strongly and catalyses the H+/H2 equilibrium.
2. So statement (d) is false.
3. Answer: (d)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 20: The chemical reaction 2AgCl(s) + H2(g) → 2HCl(aq) + 2Ag(s) taking place in a galvanic cell is represented by the notation:
(a) Pt(s)|H2(g), 1 bar|1 M KCl(aq)|AgCl(s)|Ag(s)
(b) Pt(s)|H2(g), 1 bar|1 M HCl(aq)|1 M Ag(aq)|Ag(s)
(c) Pt(s)|H2(g), 1 bar|1 M HCl(aq)|AgCl(s)|Ag(s)
(d) Pt(s)|H2(g), 1 bar|1 M HCl(aq)|Ag(s)|AgCl(s)
Show Answer & Explanation

Answer: (c) Pt(s)|H2(g), 1 bar|1 M HCl(aq)|AgCl(s)|Ag(s)

Explanation:
1. Anode (left): H2 oxidised in HCl.
2. Cathode (right): solid AgCl in contact with HCl is reduced to Ag, so the order is HCl | AgCl | Ag.
3. Answer: (c)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 21: The cell Cu | Cu2+(1 M) || Zn2+(1 M) | Zn should have an emf that is:
(a) Positive
(b) Negative
(c) Zero
(d) Cannot be predicted
Show Answer & Explanation

Answer: (b) Negative

Explanation:
1. E°cell = E°(cathode, Zn) − E°(anode, Cu) = −0.76 − 0.34 = −1.10 V.
2. The emf is negative, so the reaction is not spontaneous as written.
3. Answer: (b)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

Question 22: Which of the following is NOT an anodic reaction?
(a) Ag+ + e− → Ag
(b) Cu → Cu2+ + 2e−
(c) Fe2+ → Fe3+ + e−
(d) 4OH− → 2H2O + O2 + 4e−
Show Answer & Explanation

Answer: (a) Ag+ + e− → Ag

Explanation:
1. Anodic reactions are oxidations (loss of electrons).
2. Ag+ + e− → Ag is a reduction.
3. Answer: (a)

Teacher's Note:
1. Write the relevant formula first.
2. Check signs and units before choosing.

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FAQs

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