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?

Zinc dissolves into the solution. Signup and view all the answers

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

Electrons flow from the anode to the cathode when Eext > 1.1 V. Signup and view all the answers

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

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

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

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

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

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

What does molar conductivity measure in a solution?

Conductance of one mole of electrolyte Signup and view all the answers

How does molar conductivity change with concentration?

It increases with decreasing concentration Signup and view all the answers

Which equation correctly represents molar conductivity?

$rac{ ext{κ} A}{l}$ Signup and view all the answers

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

It increases Signup and view all the answers

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

The specific conductivity of the solution 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?

Area of cross section and length of electrode Signup and view all the answers

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

Decreased specific conductivity Signup and view all the answers

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

Concentration of the electrolyte Signup and view all the answers

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

It decreases and the oxidising power decreases. Signup and view all the answers

Which of the following properties can electrochemical cells determine?

Thermodynamic properties Signup and view all the answers

What is the role of the Nernst equation in electrochemistry?

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

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

Gas constant Signup and view all the answers

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

It is considered to be unity. 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?

The electrode potential decreases. Signup and view all the answers

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

Oxidising power decreases while reducing power increases. Signup and view all the answers

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

The total charge in a mole of electrons. Signup and view all the answers

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

271.6 S cm2 mol–1 Signup and view all the answers

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

By adding the conductivities of HCl and NaAc and subtracting NaCl Signup and view all the answers

What does Kohlrausch's law primarily deal with?

Determining ion mobility in solutions 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?

1.78 × 10–5 mol L–1 Signup and view all the answers

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

It will decrease Signup and view all the answers

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

The concentration of ions in solution Signup and view all the answers

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

Introduce additional ions that can affect conductivity Signup and view all the answers

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

Strong acids completely dissociate in solution Signup and view all the answers

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

$, L_m = k \times 1000 , cm^3 , L^{-1} , molarity^{-1}$ 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?

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

How is the cell constant calculated in a conductivity cell?

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

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

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

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

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

Which statement correctly describes the relation between resistance and conductivity?

As resistance increases, conductivity decreases. 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?

Lower resistance results in higher molar conductivity. Signup and view all the answers

What is the relationship between concentration and molar conductivity?

Molar conductivity generally decreases with increasing concentration. 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 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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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.