Electroanalysis: Linear Sweep Voltammetry
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Questions and Answers

What is the primary purpose of the working electrode in linear sweep voltammetry?

  • To serve as the main site for the electrochemical reaction (correct)
  • To facilitate the flow of current
  • To measure the potential of the system
  • To control the potential of the electrochemical reaction

    • What condition must be satisfied for a corrosion reaction to be spontaneous?

  • E~Cell~ > 0 (correct)
  • E~cathode~ = E~anode~
  • E~Cell~ = 0
  • E~Cell~ < 0

    • Which electrode in linear sweep voltammetry acts as a reference for measuring potential?

  • Potentiostat
  • Counter electrode
  • Working electrode
  • Ag|AgCl|Cl^- (saturated) (correct)

    • Which equation is used to relate Gibbs energy change to the corrosion reaction?

    <p>∆G = -nFE<del>Cell</del></p> Signup and view all the answers

    Why is it important that no current flows through the reference electrode?

    <p>To avoid affecting the concentration of reactants</p> Signup and view all the answers

    What type of diagrams are used to represent the regions of metal stability and corrosion potential?

    <p>Pourbaix diagrams</p> Signup and view all the answers

    What type of reactions are typically studied by sweeping the potential of the working electrode more positive than the equilibrium potential?

    <p>Oxidation reactions</p> Signup and view all the answers

    What instrument is used to control the three-electrode system in linear sweep voltammetry?

    <p>Potentiostat</p> Signup and view all the answers

    Which factors must be considered to predict corrosion occurrence aside from electrode potential?

    <p>Chemical reactions and metal oxide stability</p> Signup and view all the answers

    If the reactants are not in their standard state, which equation is necessary to evaluate corrosion potential?

    <p>Nernst Equation</p> Signup and view all the answers

    What is the function of the counter electrode in linear sweep voltammetry?

    <p>To complete the circuit and measure current</p> Signup and view all the answers

    When considering Fe corroding in acid solutions, which electrochemical process must occur at the anode?

    <p>Oxidation of Fe</p> Signup and view all the answers

    What happens to the current measured in a voltammetric experiment as the potential of the working electrode is varied?

    <p>It should stabilize before any further changes are made</p> Signup and view all the answers

    What is the primary driving force behind the corrosion process?

    <p>Electrode potential difference</p> Signup and view all the answers

    Which statement correctly describes the typical starting point for potential in linear sweep voltammetry?

    <p>It begins at the equilibrium potential</p> Signup and view all the answers

    During which conditions should the cell potential be evaluated using the Nernst Equation for Fe?

    <p>When any species is present in non-standard states</p> Signup and view all the answers

    Which of the following statements about lithium-ion batteries is TRUE?

    <p>Lithium-ion batteries require extensive charge control circuitry for safety.</p> Signup and view all the answers

    What is the primary function of the membrane electrolyte in a fuel cell?

    <p>To conduct protons from anode to cathode.</p> Signup and view all the answers

    In a fuel cell, what happens to hydrogen at the anode?

    <p>It is oxidized into protons and electrons.</p> Signup and view all the answers

    What byproducts are primarily produced by a proton exchange membrane fuel cell?

    <p>Electricity, water, and heat.</p> Signup and view all the answers

    What is a significant disadvantage of using hydrogen stored as a gas in mobile applications?

    <p>It is not ideal due to storage volume requirements.</p> Signup and view all the answers

    What is the theoretical maximum energy conversion efficiency of a fuel cell?

    <p>100%</p> Signup and view all the answers

    How does the electron produced at the anode in a fuel cell contribute to energy production?

    <p>It travels through an external circuit to do work.</p> Signup and view all the answers

    What are fuel reformers used for in fuel cell systems?

    <p>To convert hydrocarbons into usable hydrogen.</p> Signup and view all the answers

    What does the voltage between the terminals of the battery fundamentally depend on?

    <p>Overpotentials at both electrodes and the current</p> Signup and view all the answers

    What role do good electrodes play in battery design?

    <p>They reduce overpotentials and enhance reaction rates</p> Signup and view all the answers

    How does an increase in current affect the cell voltage during battery discharge?

    <p>The cell voltage decreases due to increased overpotential</p> Signup and view all the answers

    What determines the overall capacity of a battery?

    <p>The electrode with the least amount of active material</p> Signup and view all the answers

    Which factor is crucial for minimizing mass transport effects in a battery?

    <p>High surface area electrodes like powders or meshes</p> Signup and view all the answers

    The formula for calculating the capacity of a battery electrode involves which of the following?

    <p>The molar mass of the active material</p> Signup and view all the answers

    What is a common unit for battery capacity?

    <p>Ampere-hours</p> Signup and view all the answers

    What does a low internal resistance in a battery contribute to?

    <p>Higher voltage output across terminals</p> Signup and view all the answers

    What is the primary function of a sacrificial anode in corrosion protection?

    <p>To corrode in preference to the protected metal</p> Signup and view all the answers

    Which of the following statements is true regarding anodic protection?

    <p>It requires the metal to be connected to a potentiostat</p> Signup and view all the answers

    Which type of battery is designed for long-term use and can be recharged?

    <p>Secondary batteries</p> Signup and view all the answers

    What happens during the electron transfer in a battery?

    <p>Electrons flow from anode to cathode</p> Signup and view all the answers

    Which materials can serve as electrolytes in batteries?

    <p>Both solid and liquid media</p> Signup and view all the answers

    What is essential to maintain low for good efficiency in batteries?

    <p>Internal resistance</p> Signup and view all the answers

    Which statement about Gibbs energy change in batteries is correct?

    <p>It must be negative for the battery to produce electrical energy</p> Signup and view all the answers

    What is the purpose of separators in a battery?

    <p>To prevent direct contact between electrodes</p> Signup and view all the answers

    What does a battery capacity of 10 Ah imply?

    <p>The battery can supply 10 A for 1 h.</p> Signup and view all the answers

    Which factor is crucial for achieving the full capacity of a battery during discharge?

    <p>Low discharge current.</p> Signup and view all the answers

    What is the immediate consequence of discharging a battery to its full extent?

    <p>Increased rate of reactant loss.</p> Signup and view all the answers

    What is the reversible cell potential of a lead-acid battery?

    <p>2.05 V</p> Signup and view all the answers

    What reaction occurs at the cathode of a lead-acid battery during discharge?

    <p>PbO2 + 4H+ + SO4^2- + 2e^- → PbSO4 + 2H2O</p> Signup and view all the answers

    Which of the following correctly describes secondary batteries?

    <p>They are designed for repetitive charge and discharge cycles.</p> Signup and view all the answers

    What is one challenge that rechargeable batteries face over time?

    <p>The buildup of side chemical reactions.</p> Signup and view all the answers

    Which best describes the electrolyte used in lead-acid batteries?

    <p>Aqueous H2SO4 solution.</p> Signup and view all the answers

    Study Notes

    Electroanalysis - Linear Sweep Voltammetry

    • Electrochemical reactions occur at a given potential; current flows if a reaction proceeds
    • Linear sweep voltammetry measures current as potential is linearly swept from a starting to a final potential
    • A typical experiment needs three electrodes: a working electrode (where reaction occurs, often an inert metal disc like Pt or Au), a reference electrode (e.g., Ag|AgCl|Cl⁻ (saturated)) with a known potential, and a counter electrode (usually Pt) to complete the circuit
    • Current flow indicates a reaction
    • The reference electrode's potential is not affected by current flow
    • A potentiostat is used to control the three-electrode system

    Steady-State Current

    • The current predicted by the equation is the steady-state current
    • In a real experiment, the potential is swept/scanned at a controlled rate instead of step-wise

    Electrode-Solution Interface

    • A static layer of solution is weakly adsorbed onto the electrode surface
    • Natural convection keeps the bulk solution well-mixed and concentration uniform
    • As a reaction starts, the reactant concentration at the electrode surface decreases, causing a concentration gradient, which drives diffusion of reactant to the electrode

    Oxidation of Fe²⁺ to Fe³⁺

    • Example of an oxidation reaction at an electrode surface
    • Inert salt (e.g., KCl) added to ensure solution conductivity
    • Positive potential sweep allows oxidation of Fe²⁺ to Fe³⁺
    • The rate of reaction and the current increase with increasing positive potential
    • Current reaches a peak and then drops off due to decreasing concentration of Fe²⁺ at the electrode surface

    Peak Current Density

    • Calculated from the Randles-Sevcik Equation
    • Related to ionic diffusion coefficient, concentration, and scan rate
    • Used for species identification and analysis

    Cyclic Voltammetry

    • An extension of linear sweep voltammetry, where potential is swept back after reaching the final potential
    • Useful for identifying redox reactions
    • Plot of peak current density vs. square root of scan rate (linear) is used to determine diffusion coefficient and concentration

    Corrosion

    • Gradual metal breakdown from chemical/electrochemical oxidation
    • Electrons released from metal dissolution must be used up by a reaction at another site (cathodic reaction)
    • Corrosion is a steady-state reaction
    • Cathodic reactions in acid solutions and alkaline solutions are given

    Driving Force for Corrosion

    • The Gibbs free energy change (-nFEcell) is related to the equilibrium potential of the corrosion cell, implying a spontaneous reaction if E°cell is positive and AG is negative

    Pourbaix Diagrams

    • Data-driven diagrams displaying metal stability regions considering potential (E) vs pH
    • Shows stability areas for metal and its compounds in an electrolyte

    Horizontal Lines

    • Independent of pH related to electrochemical reactions involving only electrons
    • Concentration of 10⁻⁶ mol dm⁻³ typically used for corrosion analysis unless otherwise stated

    Vertical Lines

    • Equilibria involving only hydrolysis (H₂O, H⁺, OH⁻), not electrons

    Sloping Lines

    • Equilibria involving both electron transfer and hydrolysis

    Dashed Lines

    • Show potentials of O₂/H₂O and H⁺/H₂ reactions (cathodic)

    Battery Characteristics

    • Voltage depends on electrode reactions, kinetics, and internal resistance

    Battery Capacity

    • Amount of charge a battery can deliver
    • Determined by the electrode with the lowest active material amount

    Battery Cycle Life

    • Repetitive charge/discharge cycles
    • Active material reformation needed for cycle life

    Fuel Cells

    • Convert chemical energy into direct electricity and heat
    • Use chemical reactions (redox) between fuel and oxygen/air at different electrode surfaces, producing electricity and water

    Hydrogen Supply for Fuel Cells

    • Stored as gas, liquid, or a hydride
    • Some contain fuel reformers using hydrocarbon fuels

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    CH212 Electrochemistry Past Paper 2024-25 PDF

    Description

    Explore the principles of linear sweep voltammetry in electroanalysis. This quiz covers essential concepts such as current measurement in electrochemical reactions, the three-electrode system, and factors affecting steady-state current. Test your understanding of the electrode-solution interface and the applications of potentiostats.

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