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Questions and Answers
What happens in a cell when the external potential is set to exactly 1.1 V?
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?
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?
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?
What occurs at the anode when the external potential exceeds 1.1 V?
Which statement about electron flow in the described cell is accurate?
Which statement about electron flow in the described cell is accurate?
How does the electrochemical behavior of a Daniell cell differ from an electrolytic cell?
How does the electrochemical behavior of a Daniell cell differ from an electrolytic cell?
What must occur for a chemical reaction to be non-spontaneous in an electrolytic cell?
What must occur for a chemical reaction to be non-spontaneous in an electrolytic cell?
What does the presence of an external potential greater than 1.1 V indicate regarding the reaction?
What does the presence of an external potential greater than 1.1 V indicate regarding the reaction?
What does molar conductivity measure in a solution?
What does molar conductivity measure in a solution?
How does molar conductivity change with concentration?
How does molar conductivity change with concentration?
Which equation correctly represents molar conductivity?
Which equation correctly represents molar conductivity?
What happens to the volume of solution containing one mole of electrolyte when diluted?
What happens to the volume of solution containing one mole of electrolyte when diluted?
What does the variable 'k' represent in the context of conductivity?
What does the variable 'k' represent in the context of conductivity?
In the equation $ ext{Λm} = rac{ ext{κ} A}{l}$, what do A and l represent when they are set to unity?
In the equation $ ext{Λm} = rac{ ext{κ} A}{l}$, what do A and l represent when they are set to unity?
What compensates for the increase in volume during dilution when evaluating conductivity?
What compensates for the increase in volume during dilution when evaluating conductivity?
Which factor directly affects the molar conductivity of an electrolyte solution?
Which factor directly affects the molar conductivity of an electrolyte solution?
What happens to the standard electrode potential as one moves from top to bottom in Table 2.1?
What happens to the standard electrode potential as one moves from top to bottom in Table 2.1?
Which of the following properties can electrochemical cells determine?
Which of the following properties can electrochemical cells determine?
What is the role of the Nernst equation in electrochemistry?
What is the role of the Nernst equation in electrochemistry?
In the Nernst equation, what does the variable 'R' represent?
In the Nernst equation, what does the variable 'R' represent?
What must be true for the concentration of solid M in the Nernst equation?
What must be true for the concentration of solid M in the Nernst equation?
If the concentration of Mn+ decreases, what is the expected effect on the electrode potential according to the Nernst equation?
If the concentration of Mn+ decreases, what is the expected effect on the electrode potential according to the Nernst equation?
Which statement is true regarding the oxidising and reducing power of species in electrochemical reactions?
Which statement is true regarding the oxidising and reducing power of species in electrochemical reactions?
What is Faraday's constant represented by in the Nernst equation?
What is Faraday's constant represented by in the Nernst equation?
What is the molar conductivity of CaCl2 calculated using Kohlrausch's law?
What is the molar conductivity of CaCl2 calculated using Kohlrausch's law?
How is the molar conductivity of acetic acid determined from other conductivities?
How is the molar conductivity of acetic acid determined from other conductivities?
What does Kohlrausch's law primarily deal with?
What does Kohlrausch's law primarily deal with?
What is the dissociation constant (k) of acetic acid when its conductivity is given as 4.95 × 10–5 S cm–1?
What is the dissociation constant (k) of acetic acid when its conductivity is given as 4.95 × 10–5 S cm–1?
What will happen to the conductivity of a solution as it gets diluted?
What will happen to the conductivity of a solution as it gets diluted?
Which of the following is necessary to calculate the molar conductivity of a substance?
Which of the following is necessary to calculate the molar conductivity of a substance?
What would likely happen if you added sodium chloride to a solution of acetic acid?
What would likely happen if you added sodium chloride to a solution of acetic acid?
Why might the molar conductivity of acetic acid differ from that of strong acids?
Why might the molar conductivity of acetic acid differ from that of strong acids?
What is the formula used to calculate the molar conductivity ($, L_m$) from conductivity ($, k$) and concentration ($, c$)?
What is the formula used to calculate the molar conductivity ($, L_m$) from conductivity ($, k$) and concentration ($, c$)?
If the resistance ($, R$) of a conductivity cell filled with 0.02 mol L–1 KCl solution is 520 Ω, what is the conductivity ($, k$) of this solution?
If the resistance ($, 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?
How is the cell constant calculated in a conductivity cell?
How is the cell constant calculated in a conductivity cell?
Which of the following unit conversion is correct for molar conductivity from $S , m^2 , mol^{-1}$ to $S , cm^2 , mol^{-1}$?
Which of the following unit conversion is correct for molar conductivity from $S , m^2 , mol^{-1}$ to $S , cm^2 , mol^{-1}$?
What is the molar conductivity of a 0.02 mol L–1 KCl solution, given its conductivity is $0.248 , S , m^{-1}$?
What is the molar conductivity of a 0.02 mol L–1 KCl solution, given its conductivity is $0.248 , S , m^{-1}$?
Which statement correctly describes the relation between resistance and conductivity?
Which statement correctly describes the relation between resistance and conductivity?
For a solution with a given concentration, how does a change in resistance affect the calculation of molar conductivity?
For a solution with a given concentration, how does a change in resistance affect the calculation of molar conductivity?
What is the relationship between concentration and molar conductivity?
What is the relationship between concentration and molar conductivity?
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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 Trends
- 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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