60 free MCQs on Electrochemistry with worked answers and explanations. Explore the link between chemical reactions and electricity. Covers galvanic cells, electrolysis, standard electrode potentials, the Nernst equation, and real-world applications like batteries and corrosion.
Take the timed Electrochemistry chapterwise test →Below are 60 practice questions on Electrochemistry, sorted Easy → Hard. Tap “Show answer & explanation” under any question to check yourself. Want the full theory first? Read the Electrochemistry notes.
In a Daniell cell, electrons flow externally from the zinc anode (oxidation) through the voltmeter to the copper cathode (reduction), while the salt bridge completes the circuit.
Q1.
Electrolysis uses electricity to:
Answer: B. Drive non-spontaneous chemical reactions
Why: Electrolysis uses electrical energy to force non-spontaneous reactions (decomposition) to occur.
Q2.
In an electrolytic cell, reduction occurs at the:
Answer: B. Cathode
Why: The cathode is the negative electrode where cations gain electrons (reduction occurs).
Q3.
In a galvanic cell, the anode is the:
Answer: B. Negative electrode
Why: In a galvanic cell, the anode is negative and undergoes oxidation (loss of electrons).
Q4.
The EMF of a cell is measured in:
Answer: C. Volt
Why: Electromotive force (EMF) is the potential difference between electrodes, measured in volts (V).
Q5.
The standard hydrogen electrode is assigned a potential of:
Answer: C. 0 V
Why: The standard hydrogen electrode (SHE) is assigned exactly 0 V by international convention.
Q6.
Which process always occurs at the anode?
Answer: B. Oxidation
Why: Oxidation (loss of electrons) always occurs at the anode in both electrolytic and galvanic cells.
Q7.
One Faraday (F) is the charge carried by:
Answer: C. One mole of electrons
Why: 1 Faraday = 96500 C/mol, the charge carried by exactly one mole of electrons.
Q8.
In the Daniell cell, which metal acts as the anode?
Answer: B. Zinc
Why: Zinc is more reactive and is oxidised at the anode: Zn → Zn²⁺ + 2e⁻.
Q9.
The conductivity of a metallic conductor with increasing temperature:
Answer: B. Decreases
Why: In metals, higher temperature causes more ionic vibrations, increasing resistance and decreasing conductivity.
Q10.
Faraday's first law of electrolysis states that mass deposited is proportional to:
Answer: C. Charge passed
Why: m = ZQ, where Z is electrochemical equivalent and Q is total charge passed through the electrolyte.
Q11.
A device that converts chemical energy into electrical energy is a:
Answer: B. galvanic cell
Why: A galvanic (voltaic) cell uses a spontaneous redox reaction to produce electricity.
Q12.
In a galvanic cell, oxidation takes place at the:
Answer: B. anode
Why: Oxidation always occurs at the anode; reduction at the cathode.
Q13.
In any electrochemical cell, reduction occurs at the:
Answer: B. cathode
Why: Reduction (gain of electrons) takes place at the cathode.
Q14.
The main function of a salt bridge is to:
Answer: B. maintain electrical neutrality
Why: The salt bridge completes the circuit and keeps both half-cells electrically neutral as ions are used up.
Q15.
The SI unit of electric charge is the:
Answer: B. the coulomb
Why: Charge is measured in coulombs (C); the volt, ampere and ohm measure potential, current and resistance.
Q16.
One faraday of electric charge is approximately:
Answer: A. 96500 C
Why: One faraday is the charge on one mole of electrons, about 96500 coulombs.
Q17.
The standard reduction potential of the standard hydrogen electrode is taken as:
Answer: B. 0 V
Why: The SHE is the reference electrode, assigned a potential of exactly 0 V.
Q18.
The rate of flow of electric charge (current) is measured in:
Answer: B. in amperes
Why: Electric current is measured in amperes (A).
Q19.
Electrolysis is the decomposition of a compound brought about by passing:
Answer: B. an electric current
Why: In electrolysis, an electric current drives an otherwise non-spontaneous chemical decomposition.
Q20.
In the electrochemical series, a species that is more easily reduced has a:
Answer: B. higher reduction potential
Why: The more positive (higher) the standard reduction potential, the greater the tendency to be reduced.
Q21.
The standard EMF of the Daniell cell (Zn-Cu) is approximately:
Answer: C. 1.10 V
Why: E°cell = E°cathode - E°anode = +0.34 V (Cu) - (-0.76 V) (Zn) = 1.10 V.
Q22.
The relationship between ΔG° and E°cell is:
Answer: B. ΔG° = -nFE°
Why: ΔG° = -nFE°. A positive E° means negative ΔG° (spontaneous reaction).
Q23.
During electrolysis of dilute H₂SO₄, the gas at the cathode is:
Answer: B. H₂
Why: H⁺ ions are reduced at cathode: 2H⁺ + 2e⁻ → H₂. Hydrogen gas evolves.
Q24.
Kohlrausch's law states that at infinite dilution, molar conductance equals:
Answer: B. Sum of individual ionic conductances
Why: At infinite dilution ions act independently. ΔM∞ = λ⁺ + λ⁻ (sum of limiting ionic conductances).
Q25.
The Nernst equation is used to calculate:
Answer: B. EMF at non-standard conditions
Why: Nernst equation: E = E° - (RT/nF) ln Q. It gives cell EMF when concentrations differ from 1 M.
Q26.
Faraday's second law: for the same quantity of charge, masses deposited are proportional to:
Answer: B. Equivalent masses
Why: Equal charges deposit masses proportional to equivalent mass (molar mass / n) of each substance.
Q27.
Molar conductance of an electrolyte solution increases on dilution because:
Answer: C. Ionic association decreases, giving more free ions
Why: On dilution, ion-ion interactions decrease and ionic mobility increases, raising molar conductance.
Q28.
Which device requires an external source of EMF to operate?
Answer: C. Electrolytic cell
Why: An electrolytic cell uses external electrical energy to drive a non-spontaneous chemical reaction.
Q29.
Why does the conductivity of a strong electrolyte solution decrease as its concentration increases, even though molar conductivity is being measured?
Answer: A. Increased ionic interactions at higher concentration reduce the ease with which ions move and carry charge per mole
Why: As concentration increases, inter-ionic attractions become more significant, which reduces ionic mobility and lowers the molar conductivity, even though total conductivity may rise due to more ions being present.
Q30.
In a galvanic cell such as the Daniell cell, electrons flow through the external circuit from the:
Answer: C. Zinc anode to the copper cathode
Why: In a galvanic cell, oxidation occurs at the zinc anode, releasing electrons that travel through the external wire to the copper cathode where reduction occurs.
Q31.
The standard EMF of a cell is E°cell = E°cathode −:
Answer: A. E°anode
Why: E°cell = E°cathode − E°anode, both taken as standard reduction potentials.
Q32.
By Faraday’s first law of electrolysis, the mass of a substance deposited is proportional to the:
Answer: B. the quantity of charge
Why: Faraday’s first law: mass deposited ∝ quantity of electric charge (Q = It) passed through the cell.
Q33.
For a spontaneous cell reaction, the standard cell potential E°cell is:
Answer: B. positive
Why: A spontaneous cell reaction has a positive E°cell, corresponding to a negative ΔG°.
Q34.
The relationship between standard free energy and cell potential is ΔG° =:
Answer: B. −nFE°cell
Why: ΔG° = −nFE°cell, so a positive E°cell gives a negative ΔG° (spontaneous).
Q35.
The conductivity (specific conductance) of an electrolyte solution, on dilution:
Answer: B. decreases
Why: Conductivity falls on dilution because the number of ions per unit volume decreases.
Q36.
The molar conductivity of an electrolyte solution, on dilution:
Answer: B. increases
Why: Molar conductivity rises on dilution as ions move more freely and (for weak electrolytes) dissociation increases.
Q37.
Kohlrausch’s law expresses the limiting molar conductivity as the sum of contributions from the individual:
Answer: B. ions
Why: Each ion contributes independently to the limiting molar conductivity (law of independent migration of ions).
Q38.
During the electrolysis of molten sodium chloride, sodium metal is deposited at the:
Answer: B. cathode
Why: Na⁺ ions gain electrons (reduction) at the cathode to form sodium metal.
Q39.
The number of electrons involved in the reduction Cu²⁺ + 2e⁻ → Cu is:
Answer: B. 2
Why: The half-reaction shows two electrons are gained per copper ion.
Q40.
A secondary cell differs from a primary cell in that it can be:
Answer: B. recharged
Why: A secondary cell (e.g. a lead-acid battery) is rechargeable by reversing the cell reaction.
Q41.
For Zn|Zn²⁺(0.1M)||Cu²⁺(0.01M)|Cu with E°cell = 1.10 V at 298 K, the cell EMF is:
Answer: A. 1.07 V
Why: E = E° - (0.0591/2)log([Zn²⁺]/[Cu²⁺]) = 1.10 - 0.02955×log(0.1/0.01) = 1.10 - 0.02955 = 1.07 V.
Q42.
Mass of silver deposited when 2 A passes for 1930 s (Ag = 108, F = 96500 C) is:
Answer: A. 4.32 g
Why: Q = 2 × 1930 = 3860 C. Moles of e⁻ = 3860/96500 = 0.04 mol. Mass = 0.04 × 108 = 4.32 g.
Q43.
Electrode potential of Cu²⁺/Cu when [Cu²⁺] = 0.01 M at 298 K (E° = +0.34 V) is:
Answer: A. +0.281 V
Why: E = E° - (0.0591/2)log(1/[Cu²⁺]) = 0.34 - (0.02955)log(100) = 0.34 - 0.0591 = 0.281 V.
Q44.
Which electrode has the highest standard reduction potential?
Answer: D. F₂/F⁻ (+2.87 V)
Why: Fluorine has the highest standard reduction potential (+2.87 V), making it the strongest oxidising agent.
Q45.
The Debye-Huckel-Onsager equation for molar conductance vs concentration is:
Answer: A. Λm = Λ°m - K√c
Why: Λm = Λ°m - K√c. Molar conductance decreases with the square root of concentration due to interionic interactions.
Q46.
In electrolysis of aqueous CuSO₄ using Pt electrodes, what forms at the anode?
Answer: B. O₂ evolves
Why: At the inert Pt anode, water is oxidised: 2H₂O → O₂ + 4H⁺ + 4e⁻. Oxygen gas evolves.
Q47.
For a cell with E = 1.1 V and n = 2, the Gibbs energy change is:
Answer: A. -212.3 kJ
Why: ΔG = -nFE = -2 × 96500 × 1.1 = -212,300 J = -212.3 kJ.
Q48.
In a concentration cell, the EMF is generated because:
Answer: B. Concentrations of the same electrolyte differ in the two half-cells
Why: In a concentration cell, both electrodes are identical but placed in solutions of different concentrations. The EMF arises from this difference.
Q49.
A current of 0.5 A is passed through molten Al<sub>2</sub>O<sub>3</sub> for 4825 seconds. What mass of aluminium is deposited (Al = 27 g/mol, F = 96500 C)?
Answer: C. 0.225 g
Why: Moles of electrons = It/F = (0.5 x 4825)/96500 = 0.025; Al<sup>3+</sup> + 3e- -> Al, so moles of Al = 0.025/3 = 0.00833, mass = 0.00833 x 27 = 0.225 g.
Q50.
For the cell reaction Ni(s) + Cu<sup>2+</sup>(aq) -> Ni<sup>2+</sup>(aq) + Cu(s) with E°cell = 0.57 V at 298 K, what is the equilibrium constant K for this reaction (n = 2)?
Answer: C. Approximately 1.9 x 10<sup>19</sup>
Why: log K = nE°/0.0591 = (2 x 0.57)/0.0591 = 19.3, so K = 10<sup>19.3</sup>, approximately 1.9 x 10<sup>19.</sup>
Q51.
In the Nernst equation E = E° − (0.059/n) log Q at 298 K, n represents the number of:
Answer: B. electrons transferred
Why: n is the number of moles of electrons transferred in the balanced cell reaction.
Q52.
The quantity of charge required to deposit one mole of aluminium from Al³⁺ is:
Answer: C. 3 faradays
Why: Al³⁺ + 3e⁻ → Al requires three moles of electrons, i.e. 3 faradays.
Q53.
The mass of copper deposited by passing 2 faradays of charge through CuSO₄ solution is (Cu = 63.5):
Answer: B. 63.5 g
Why: Cu²⁺ + 2e⁻ → Cu, so 2 F deposits one mole of copper = 63.5 g.
Q54.
The molar conductivity of an electrolyte at infinite dilution is called its:
Answer: B. limiting molar conductivity
Why: Extrapolated to infinite dilution, the molar conductivity reaches its limiting value, Λ°ₘ.
Q55.
For a concentration cell, the standard cell potential E°cell is:
Answer: B. zero
Why: Both electrodes are identical in a concentration cell, so E°cell = 0 and the EMF arises only from the concentration difference.
Q56.
The equation E°cell = (0.059/n) log Kc allows calculation of the:
Answer: B. equilibrium constant
Why: This links the standard cell potential to the equilibrium constant Kc of the cell reaction.
Q57.
The electrolyte used in a common lead storage battery is:
Answer: B. sulfuric acid
Why: The lead-acid accumulator uses about 38% sulfuric acid as its electrolyte.
Q58.
The cell constant of a conductivity cell is equal to:
Answer: B. length ÷ area
Why: Cell constant = l/A (distance between electrodes divided by their area), with units of cm⁻¹.
Q59.
If the standard cell potential E°cell is positive, the equilibrium constant K of the reaction is:
Answer: B. greater than 1
Why: A positive E°cell means a negative ΔG°, so K > 1 and products are favoured.
Q60.
The rusting of iron in moist air is fundamentally a(n):
Answer: B. electrochemical process
Why: Rusting sets up tiny galvanic cells on the iron surface, making corrosion an electrochemical process.