Electrochemistry

Electrochemistry MDCAT MCQs with answers

54 past paper MCQs from Chemistry unit 9, Electrochemistry, across 4 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Redox Reactions

1.An electrochemical cell is based upon which reaction? (MDCAT 2022)

  1. acid-base reaction
  2. redox reaction
  3. nuclear reaction
  4. neutralization reaction
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Correct answer: (b) redox reaction

The cell works by separating the oxidation and the reduction, so the electrons travel through the external circuit.

2.Which of the following situations most clearly demonstrates a key characteristic of a Redox reaction? (UHS MDCAT 2025)

  1. Water boiling to steam
  2. Hydrogen gas reacting with chlorine to form hydrogen chloride gas
  3. Sodium chloride dissolving in water
  4. Ethanol evaporating at room temperature
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Correct answer: (b) Hydrogen gas reacting with chlorine to form hydrogen chloride gas

Hydrogen loses electrons to chlorine; the other three changes are physical.

3.Placing a rod of iron metal in a solution of CuSO4: (NUMS MDCAT 2024)

  1. Cu will be deposited
  2. Fe is precipitated out
  3. Cu and Fe both dissolve
  4. No reaction taken place
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Correct answer: (a) Cu will be deposited

Iron is above copper in the reactivity series, so it displaces copper from the solution.

All 9 Redox Reactions MCQs → Redox Reactions notes →

Oxidation and Reduction

4.In which of the following does oxygen show a fractional oxidation number? (MDCAT 2022)

  1. $\mathrm{OF_2}$
  2. $\mathrm{Na_2O_2}$
  3. $\mathrm{KO_2}$
  4. $\mathrm{Cl_2O_7}$
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Correct answer: (c) $\mathrm{KO_2}$

In the superoxide $\mathrm{KO_2}$ the two oxygens share a single negative charge, so each is $-\tfrac{1}{2}$.

5.Which statement describes the conversion of magnesium atoms to magnesium ions for ionic bond formation with chlorine? (MDCAT 2022)

  1. the change is reduction, because there has been a gain of electrons
  2. the change is oxidation, because there has been a loss of electrons
  3. the change is reduction, because there has been a loss of electrons
  4. the change is oxidation, because there has been a gain of electrons
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Correct answer: (b) the change is oxidation, because there has been a loss of electrons

Mg loses two electrons to become $\mathrm{Mg^{2+}}$, and loss of electrons is oxidation.

6.The oxidation number of a free element is: (MDCAT 2023)

  1. zero
  2. $+1$
  3. $-1$
  4. equal to its group number
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Correct answer: (a) zero

An uncombined atom has shared its electrons with nothing, so its oxidation number is zero.

All 26 Oxidation and Reduction MCQs → Oxidation and Reduction notes →

Balancing Redox Equations

7.Which step is irrelevant with respect to balancing redox equations by the oxidation number method? (MDCAT 2024)

  1. split the reaction into two half reactions
  2. assign oxidation numbers to all the atoms involved in the equation
  3. identify the element undergoing a change in oxidation number
  4. equalize the number of electrons lost and gained
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Correct answer: (a) split the reaction into two half reactions

Splitting into half reactions belongs to the ion-electron method, not to the oxidation number method.

8.Which step is irrelevant with respect to balancing of redox equations by oxidation number method? (UHS MDCAT 2024)

  1. Split the reaction into two half reactions
  2. Assign oxidation number to all the atoms involved in the equation
  3. Identify the element undergoing a change in oxidation number
  4. Equalize the number of electrons lost and gained
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Correct answer: (a) Split the reaction into two half reactions

Splitting into half reactions belongs to the ion electron method, not to the oxidation number method.

9.In the ion-electron method of balancing equations, how oxygen is balanced? (PMC MDCAT 2022)

  1. O is balanced by adding O2
  2. O is balanced by adding H2O
  3. O is balanced by adding OH
  4. All the ways are used
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Correct answer: (b) O is balanced by adding H2O

Oxygen is balanced by adding water to the side short of it, and hydrogen then by adding protons.

Balancing Redox Equations notes →

Standard Hydrogen Electrode

10.The stronger the oxidizing agent, the greater is its: (MDCAT 2020)

  1. oxidation potential
  2. reduction potential
  3. redox potential
  4. emf
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Correct answer: (b) reduction potential

An oxidizing agent is itself reduced, so the more readily it takes electrons the higher its standard reduction potential.

11.When SHE is connected with Cu electrode using salt bridge and external wire: (SIBA MDCAT 2025)

  1. Cu reduces
  2. Cu+2 reduces
  3. H+ reduces
  4. H2 reduces
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Correct answer: (b) Cu+2 reduces

Copper stands above hydrogen in the electrochemical series, so the copper ions take the electrons and the copper electrode is the cathode.

12.In a standard hydrogen electrode, the platinum electrode: (SZABMU MDCAT 2025)

  1. Reacts with hydrogen
  2. Provide a surface for oxidation and reduction.
  3. Acts as a salt bridge.
  4. Provide voltage to the circuit.
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Correct answer: (b) Provide a surface for oxidation and reduction.

The platinum is inert; it only carries the electrons and offers a surface for the hydrogen.

All 16 Standard Hydrogen Electrode MCQs → Standard Hydrogen Electrode notes →

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