Electrolytic Cells and Reactions
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Questions and Answers

What happens in a cell when the external potential is set to exactly 1.1 V?

  • Zinc dissolves at the cathode.
  • Copper deposits at the anode.
  • No flow of electrons or current occurs. (correct)
  • Current flows from the anode to the cathode.
  • In an electrolytic cell, what role does the external potential play?

  • It converts chemical energy to electrical energy.
  • It maintains the spontaneous reaction of the cell.
  • It helps initiate and sustain a non-spontaneous reaction. (correct)
  • It prevents any reaction from occurring.
  • When the external potential is less than 1.1 V, what occurs?

  • Electrons flow from the copper rod to the zinc rod.
  • Electron flow is from zinc to copper, resulting in current flow from copper to zinc. (correct)
  • No current flows and no reaction occurs.
  • Zinc ions are deposited at the anode.
  • What occurs at the anode when the external potential exceeds 1.1 V?

    <p>Zinc dissolves into the solution.</p> Signup and view all the answers

    Which statement about electron flow in the described cell is accurate?

    <p>Electrons flow from the anode to the cathode when Eext &gt; 1.1 V.</p> Signup and view all the answers

    How does the electrochemical behavior of a Daniell cell differ from an electrolytic cell?

    <p>Daniell cells rely on spontaneous reactions to generate electrical energy.</p> Signup and view all the answers

    What must occur for a chemical reaction to be non-spontaneous in an electrolytic cell?

    <p>An external potential must be applied to drive the reaction.</p> Signup and view all the answers

    What does the presence of an external potential greater than 1.1 V indicate regarding the reaction?

    <p>The reaction will reverse and operate as an electrolytic cell.</p> Signup and view all the answers

    What does molar conductivity measure in a solution?

    <p>Conductance of one mole of electrolyte</p> Signup and view all the answers

    How does molar conductivity change with concentration?

    <p>It increases with decreasing concentration</p> Signup and view all the answers

    Which equation correctly represents molar conductivity?

    <p>$ rac{ ext{κ} A}{l}$</p> Signup and view all the answers

    What happens to the volume of solution containing one mole of electrolyte when diluted?

    <p>It increases</p> Signup and view all the answers

    What does the variable 'k' represent in the context of conductivity?

    <p>The specific conductivity of the solution</p> Signup and view all the answers

    In the equation $ ext{Λm} = rac{ ext{κ} A}{l}$, what do A and l represent when they are set to unity?

    <p>Area of cross section and length of electrode</p> Signup and view all the answers

    What compensates for the increase in volume during dilution when evaluating conductivity?

    <p>Decreased specific conductivity</p> Signup and view all the answers

    Which factor directly affects the molar conductivity of an electrolyte solution?

    <p>Concentration of the electrolyte</p> Signup and view all the answers

    What happens to the standard electrode potential as one moves from top to bottom in Table 2.1?

    <p>It decreases and the oxidising power decreases.</p> Signup and view all the answers

    Which of the following properties can electrochemical cells determine?

    <p>Thermodynamic properties</p> Signup and view all the answers

    What is the role of the Nernst equation in electrochemistry?

    <p>To relate standard electrode potentials to non-standard conditions.</p> Signup and view all the answers

    In the Nernst equation, what does the variable 'R' represent?

    <p>Gas constant</p> Signup and view all the answers

    What must be true for the concentration of solid M in the Nernst equation?

    <p>It is considered to be unity.</p> Signup and view all the answers

    If the concentration of Mn+ decreases, what is the expected effect on the electrode potential according to the Nernst equation?

    <p>The electrode potential decreases.</p> Signup and view all the answers

    Which statement is true regarding the oxidising and reducing power of species in electrochemical reactions?

    <p>Oxidising power decreases while reducing power increases.</p> Signup and view all the answers

    What is Faraday's constant represented by in the Nernst equation?

    <p>The total charge in a mole of electrons.</p> Signup and view all the answers

    What is the molar conductivity of CaCl2 calculated using Kohlrausch's law?

    <p>271.6 S cm2 mol–1</p> Signup and view all the answers

    How is the molar conductivity of acetic acid determined from other conductivities?

    <p>By adding the conductivities of HCl and NaAc and subtracting NaCl</p> Signup and view all the answers

    What does Kohlrausch's law primarily deal with?

    <p>Determining ion mobility in solutions</p> Signup and view all the answers

    What is the dissociation constant (k) of acetic acid when its conductivity is given as 4.95 × 10–5 S cm–1?

    <p>1.78 × 10–5 mol L–1</p> Signup and view all the answers

    What will happen to the conductivity of a solution as it gets diluted?

    <p>It will decrease</p> Signup and view all the answers

    Which of the following is necessary to calculate the molar conductivity of a substance?

    <p>The concentration of ions in solution</p> Signup and view all the answers

    What would likely happen if you added sodium chloride to a solution of acetic acid?

    <p>Introduce additional ions that can affect conductivity</p> Signup and view all the answers

    Why might the molar conductivity of acetic acid differ from that of strong acids?

    <p>Strong acids completely dissociate in solution</p> Signup and view all the answers

    What is the formula used to calculate the molar conductivity ($, L_m$) from conductivity ($, k$) and concentration ($, c$)?

    <p>$, L_m = k \times 1000 , cm^3 , L^{-1} , molarity^{-1}$</p> Signup and view all the answers

    If the resistance ($, R$) of a conductivity cell filled with 0.02 mol L–1 KCl solution is 520 Ω, what is the conductivity ($, k$) of this solution?

    <p>$0.248 , S , m^{-1}$</p> Signup and view all the answers

    How is the cell constant calculated in a conductivity cell?

    <p>$, G^* = conductivity \times resistance$</p> Signup and view all the answers

    Which of the following unit conversion is correct for molar conductivity from $S , m^2 , mol^{-1}$ to $S , cm^2 , mol^{-1}$?

    <p>$1 , S , m^2 , mol^{-1} = 10^4 , S , cm^2 , mol^{-1}$</p> Signup and view all the answers

    What is the molar conductivity of a 0.02 mol L–1 KCl solution, given its conductivity is $0.248 , S , m^{-1}$?

    <p>$124 , S , cm^2 , mol^{-1}$</p> Signup and view all the answers

    Which statement correctly describes the relation between resistance and conductivity?

    <p>As resistance increases, conductivity decreases.</p> Signup and view all the answers

    For a solution with a given concentration, how does a change in resistance affect the calculation of molar conductivity?

    <p>Lower resistance results in higher molar conductivity.</p> Signup and view all the answers

    What is the relationship between concentration and molar conductivity?

    <p>Molar conductivity generally decreases with increasing concentration.</p> Signup and view all the answers

    Study Notes

    Electrochemical Reactions

    • Increasing external potential beyond 1.1 V reverses the cell's reaction direction.
    • At this potential, the system operates as an electrolytic cell, utilizing electrical energy to drive non-spontaneous reactions.
    • Daniell cell utilizes zinc and copper electrodes submerged in their respective salt solutions.

    Current Flow Dynamics

    • At E_ext < 1.1 V, electrons flow from zinc (anode) to copper (cathode), creating current from copper to zinc.
    • At E_ext = 1.1 V, no current or chemical reaction occurs.
    • When E_ext exceeds 1.1 V, zinc dissolves at the anode while copper is deposited at the cathode.

    Conductivity and Molar Conductivity

    • Kohlrausch's law allows calculation of molar conductivities:
      • For CaCl2: λ°(CaCl2) = λ°(Ca²+) + 2λ°(Cl⁻) = 119.0 + 2(76.3) = 271.6 S cm² mol⁻¹
      • For MgSO4: λ°(MgSO4) = λ°(Mg²+) + λ°(SO₄²⁻) = 106.0 + 160.0 = 266 S cm² mol⁻¹

    Example Calculations

    • Molar conductivity of acetic acid (HAc) determined as follows:
      • λ°(HAc) = λ°(HCl) + λ°(NaAc) - λ°(NaCl) = 425.9 + 91.0 - 126.4 = 390.5 S cm² mol⁻¹
    • Dissociation constant calculation involves conductivity, concentration, and molar conductivity.
    • Conductivity of a solution decreases with dilution due to reduced concentration of charge carriers.
    • The relationship between conductivity (κ) and molar conductivity (λ_m) establishes the basis for various calculations:
      • λ_m = κ × (1000 / concentration)

    Cell Resistance and Conductivity

    • Example: Resistance of a cell filled with 0.1 mol L⁻¹ KCl is 100 Ω, and 0.02 mol L⁻¹ is 520 Ω.
    • Conductivity found using cell constant: κ = cell constant / resistance.
    • Molar conductivity for 0.02 mol L⁻¹ KCl can be calculated using κ.

    Electrochemical Cell Applications

    • Electrochemical cells are used for:
      • Determining pH of solutions.
      • Evaluating solubility products and equilibrium constants.
      • Conducting potentiometric titrations.

    Nernst Equation

    • The Nernst equation relates electrode potential to ion concentration:
      • E(Mn+/M) = E°(Mn+/M) - (RT/nF) ln [Mn⁺]
    • Important constants in the equation:
      • R = gas constant (8.314 J K⁻¹ mol⁻¹)
      • F = Faraday's constant (96487 C mol⁻¹)
      • T = temperature in Kelvin

    Key Concepts

    • Standard electrode potential decreases down the electrochemical series, leading to increased reducing power on the right side of reactions.
    • Conductance is defined as the ability of a solution to conduct electricity based on the electrolyte's presence and concentration.

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    Description

    This quiz explores the principles of electrolytic cells and their function in driving non-spontaneous chemical reactions using electrical energy. You'll learn the conditions that cause these reactions to reverse and the underlying concepts of electrochemistry.

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