15 extra multiple-choice questions for Electro Chemistry (12th Standard Chemistry, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
According to Ohm's law, at a constant temperature, the current (\(I\)) flowing through a conductivity cell is directly proportional to the applied voltage (\(V\)) and inversely proportional to which factor?
- A. Conductance
- B. Concentration
- C. ResistanceCorrect
- D. Temperature
Explanation. Ohm's law states that the potential difference across a conductor is the product of current and resistance, making current inversely proportional to resistance.
Q2
The specific resistance or resistivity (\(\rho\)) of an electrolytic solution is an intensive property that depends primarily on which of the following?
- A. Surface area of the electrodes
- B. Distance between the electrodes
- C. Nature of the electrolyteCorrect
- D. Total volume of the solution
Explanation. Resistivity is a characteristic property of the material itself and does not change based on the physical size or shape of the sample.
Q3
Why is an alternating current (AC) source used instead of a direct current (DC) source when measuring the conductivity of an ionic solution using a Wheatstone bridge?
- A. To increase the measured resistance
- B. To prevent the electrolysis of the solutionCorrect
- C. To simplify the circuit diagram
- D. To reduce the required voltage
Explanation. Using DC current would cause chemical decomposition and change the ion concentration at the electrodes, whereas high-frequency AC prevents these electrolytic changes.
Q4
Which type of electrochemical device utilizes an electric current from an external source to drive a non-spontaneous chemical reaction?
- A. Galvanic cell
- B. Voltaic cell
- C. Electrolytic cellCorrect
- D. Fuel cell
Explanation. Electrolytic cells perform work on the chemical system to force a reaction that has a positive change in Gibbs free energy.
Q5
In the standard Daniel cell, which metal serves as the anode where oxidation occurs during discharge?
- A. Copper
- B. Platinum
- C. ZincCorrect
- D. Silver
Explanation. The zinc electrode undergoes oxidation, losing electrons to become \(Zn^{2+}\) ions, making it the anode in a galvanic cell.
Q6
What is the primary function of the salt bridge in a galvanic cell like the Daniel cell?
- A. To provide a path for electron flow
- B. To maintain electrical neutrality in both half-cellsCorrect
- C. To act as a catalyst for the redox reaction
- D. To separate the liquid and solid phases
Explanation. The salt bridge allows ions to move between the anodic and cathodic compartments to balance the charge buildup caused by oxidation and reduction.
Q7
According to IUPAC galvanic cell notation, where is the cathode half-cell traditionally positioned relative to the salt bridge?
- A. On the left side
- B. On the right sideCorrect
- C. Between two phase boundaries
- D. On the extreme left
Explanation. By international convention, the anode half-cell is written on the left and the cathode half-cell is written on the right of the double vertical bar.
Q8
The electromotive force (emf) is the potential difference between two electrodes. What is the SI unit for cell potential?
- A. Coulomb
- B. Joule
- C. VoltCorrect
- D. Ampere
Explanation. Cell potential represents the electrical pressure driving the flow of current and is measured in volts.
Q9
What is the arbitrarily assigned electrode potential value for the Standard Hydrogen Electrode (SHE) at all temperatures?
- A. 1.00 V
- B. 0.00 VCorrect
- C. 0.76 V
- D. -0.34 V
Explanation. The SHE serves as a universal reference point for measuring the potential of other electrodes and is defined to have zero volts.
Q10
The maximum electrical work (\(W_{max}\)) that can be obtained from a galvanic cell is equal to which thermodynamic quantity?
- A. Increase in Entropy
- B. Decrease in Internal Energy
- C. Decrease in Gibbs free energy (\(\Delta G\))Correct
- D. Increase in Enthalpy
Explanation. The Gibbs free energy change of a system at constant temperature and pressure is a measure of the maximum non-expansion work available.
Q11
Using the Nernst equation, what is the effect on the cell potential (\(E_{cell}\)) if the concentration of the products in a redox reaction is increased tenfold?
- A. The cell potential increases
- B. The cell potential decreasesCorrect
- C. The cell potential remains unchanged
- D. The cell potential drops to zero
Explanation. Increasing product concentration increases the reaction quotient \(Q\). Since the term containing \(\log Q\) is subtracted, the resulting cell potential decreases.
Q12
During the electrolysis of molten sodium chloride, which substance is produced at the graphite anode?
- A. Metallic sodium
- B. Chlorine gasCorrect
- C. Hydrogen gas
- D. Oxygen gas
Explanation. Chloride ions (\(Cl^{-}\)) migrate to the positive anode, where they undergo oxidation to release electrons and form \(Cl_{2}\) gas.
Q13
Which of the following defines the electrochemical equivalent (\(Z\)) as per Faraday's First Law of Electrolysis?
- A. Mass produced by 1 mole of electrons
- B. Mass produced by 1 coulomb of chargeCorrect
- C. Charge required to deposit 1 gram of substance
- D. Ratio of molar mass to valence
Explanation. The electrochemical equivalent is the mass of a substance deposited or liberated when one coulomb of electricity is passed through the cell.
Q14
Which of the following is categorized as a secondary battery because its electrochemical reactions are reversible?
- A. Leclanche cell
- B. Mercury button cell
- C. Lead storage batteryCorrect
- D. Dry cell battery
Explanation. Lead storage batteries allow the conversion of products back into reactants by applying an external electrical potential, making them rechargeable.
Q15
In the electrochemical series, a metal with a highly negative standard reduction potential (\(E^{\circ}\)) will likely serve as a powerful what?
- A. Oxidizing agent
- B. Reducing agentCorrect
- C. Inert electrode
- D. Catalyst
Explanation. A more negative reduction potential indicates a strong tendency to lose electrons (oxidation), which defines a powerful reducing agent.
Frequently asked questions
How many MCQs are there in Electro Chemistry?
This chapter has 15 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Chemistry MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Electro Chemistry book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
