Types of Conductance. | Electrochemistry | Chemistry | Khan Academy

Khan Academy India - English
21 Apr 202310:34
EducationalLearning
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TLDRThe video script delves into the conduction process in an electrolytic cell, drawing parallels with resistance in metallic wires. It explains how conductance (G) is calculated using the cell's dimensions and conductivity (Kappa), and introduces the concept of cell constant (G Star). The script further explores molar conductivity (Lambda M), which standardizes conductivity based on molarity, allowing for comparison of different solutions' charge transfer capabilities.

Takeaways
  • 📦 The circuit of an electrolytic cell is completed by a battery, with two plates dipped in an electrolytic solution.
  • 🧪 The length (L) is the distance between the plates, and the area (A) is the common area of the plates in the solution.
  • 🔌 Resistance (R) in a metallic wire is defined by the formula: R = ρ(L/A), where ρ is resistivity.
  • ♻️ Conductance (G) is the inverse of resistance (1/R), and conductivity (κ) is the inverse of resistivity (1/ρ).
  • 📐 Conductance G in the electrolytic cell is given by κ(A/L), where κ is conductivity.
  • 🔋 The units of conductance are Siemens (S), and the units of conductivity are Siemens per meter (S/m).
  • 🔍 The cell constant (G*) is defined as L/A for a specific cell and has units of per meter (1/m).
  • 🌡️ Conductivity in solutions depends on the concentration of solute in the solvent, leading to a focus on molar conductivity (Λ).
  • 🧮 Molar conductivity (Λ) is defined as κ divided by the molar concentration (C) of the solution.
  • 🔬 Units of molar conductivity in common practice are Siemens per centimeter squared per mole (S cm²/mol).
Q & A

  • What is an electrolytic cell?

    -An electrolytic cell is a device that uses an electric current to drive a non-spontaneous chemical reaction. It typically consists of a power source, two electrodes (anodes and cathodes), and an electrolyte solution through which ions can move to conduct electricity.

  • How is conduction taking place in the electrolytic solution?

    -Conduction in an electrolytic solution occurs through the movement of ions. When a voltage is applied, ions migrate towards the electrodes of opposite charge, facilitating the flow of electric current.

  • What is the relationship between resistance and resistivity in a metallic wire?

    -The resistance (R) of a metallic wire is directly proportional to its length (L) and inversely proportional to its cross-sectional area (a). Mathematically, R = ρ * (L / a), where ρ is the resistivity of the material.

  • How can the concept of conductance be derived from resistance?

    -Conductance (G) is the inverse of resistance (R). It can be derived by rearranging the resistance formula to G = 1 / R, which indicates the ability of a material to conduct electricity.

  • What is meant by the term 'conductivity' in the context of an electrolytic cell?

    -Conductivity (Kappa) is the inverse of resistivity and represents a material's ability to conduct electricity. In the context of an electrolytic cell, it is related to the movement of ions in the solution.

  • What are the units of conductivity?

    -The units of conductivity (Kappa) are Siemens per meter (S/m) in the International System of Units (SI), or Siemens in the centimeter-gram-second (CGS) system.

  • What is a cell constant and how is it used?

    -A cell constant (G*) is a ratio of the distance between the plates (L) to the common area of the plates (a) in an electrolytic cell. It is used to relate the measured conductance (G) to the conductivity (Kappa) of the solution, expressed as G * G* = Kappa.

  • Why is it necessary to consider the concentration of the solution when discussing conductivity?

    -The concentration of a solution is important because it determines the number of ions present, which in turn affects the ability of the solution to conduct electricity. Different concentrations will result in different conductivities.

  • What is molar conductivity and how is it defined?

    -Molar conductivity (Lambda) is a measure of the conductivity of a solution per mole of solute. It is defined as the conductivity (Kappa) divided by the molar concentration (C) of the solution.

  • How can molar conductivity be calculated in CGS units?

    -Molar conductivity in CGS units can be calculated using the formula Lambda M = Kappa (in Siemens per centimeter) / (concentration in moles per liter * 1000). The factor of 1000 accounts for the conversion between moles per liter and moles per cubic centimeter.

  • Why is it important to standardize conductivity measurements?

    -Standardizing conductivity measurements helps to compare the conductive properties of different solutions on a per mole basis, allowing for a more accurate assessment of their ability to conduct electricity.

Outlines
00:00
🔋 Electrolytic Cell Conduction and Resistance Analogy

The script begins by introducing an electrolytic cell with a power source, such as a battery, and two plates immersed in an electrolytic solution. It explains the conduction process in the solution by drawing an analogy with the resistance in a metallic wire. The resistance formula R = ρL/A is rearranged to express conductance G and conductivity Kappa, with units of Siemens (S) and Siemens per meter (S/m), respectively. The concept of cell constant (G*) is introduced, which is the ratio of the distance between plates to the common area, allowing for the calculation of the solution's conductivity without changing the cell's physical dimensions.

05:01
🌡️ Understanding Conductivity Through Molar Conductivity

This paragraph delves into the concept of molar conductivity, aiming to standardize conductivity measurements by considering the concentration of solutes in a solution. It explains the importance of molar concentration in determining the number of ions available for charge transfer, thus affecting the solution's conductivity. The molar conductivity, denoted by Lambda (Λ), is defined as the ratio of conductivity to molar concentration. The units of molar conductivity are Siemens per mole per meter square (S·m²/mol) in SI units, but for practical purposes, they are often given in Siemens per centimeter divided by moles per liter, accounting for the conversion between volume units.

10:01
📏 Calculating Molar Conductivity with Given Units

The final paragraph focuses on the practical calculation of molar conductivity using the given units of Siemens per centimeter for conductivity and moles per liter for concentration. It simplifies the process by incorporating a unit conversion that allows for direct calculation without the need for further adjustments. The formula presented is Kappa (in Siemens per centimeter) divided by the concentration in moles per liter, multiplied by 1000, resulting in molar conductivity in Siemens centimeter square per mole, a measure that helps compare the conductive properties of different solutions.

Mindmap
Keywords
💡Electrolytic cell
An electrolytic cell is a device that uses electrical energy to drive a non-spontaneous chemical reaction. In the context of the video, it involves a power source, such as a battery, and two plates (electrodes) immersed in an electrolytic solution. The conduction of electricity in this cell is through the movement of ions within the solution, which is central to the video's theme of understanding conduction in electrolytic solutions.
💡Conduction
Conduction refers to the process of transmitting heat, electricity, or sound through a medium without any movement of the medium itself. In the video, it is the mechanism by which electrons move through the electrolytic solution, facilitated by the ions present. The script discusses how conduction occurs in the solution, drawing parallels to the conduction in metallic wires.
💡Resistivity
Resistivity is a material property that quantifies how strongly a given material opposes the flow of electric current. The script explains resistivity in the context of a metallic wire and contrasts it with conductivity in an electrolytic cell. It is used to calculate resistance, which is an essential concept for understanding how different materials, including electrolytic solutions, affect electrical current.
💡Conductance
Conductance is the reciprocal of resistance and represents the ease with which an electric current can flow through a material. The video script introduces conductance as the inverse of resistance (1/R) and relates it to the concept of conductivity, which is used to describe the ability of the electrolytic solution to conduct electricity.
💡Conductivity
Conductivity (denoted as Kappa in the script) is a measure of a material's ability to conduct an electric current. It is the inverse of resistivity and is used to quantify how well the electrolytic solution in the cell can conduct electricity. The script discusses how conductivity is calculated and how it changes with different solutions.
💡Cell constant
The cell constant is a ratio of the distance between the plates (L) to the common area of the plates (a) in an electrolytic cell. It is used to standardize the measurement of conductivity across different solutions using the same cell. The script explains that the cell constant allows for the comparison of conductivities by keeping the physical dimensions of the cell constant.
💡Molar conductivity
Molar conductivity is a measure of the conductivity of a solution per mole of solute. The script introduces this term to standardize conductivity measurements by taking into account the concentration of ions in the solution. It is defined as the conductivity (Kappa) divided by the molar concentration (C), and it helps in comparing the conductive properties of different solutions.
💡Molarity
Molarity is the amount of solute dissolved in a solution, expressed in moles per liter of solution. In the script, molarity is used in the calculation of molar conductivity to account for the concentration of ions that contribute to the solution's conductivity.
💡Solute
A solute is the substance that is dissolved in a solvent to form a solution. In the context of the video, the solute is responsible for the ions in the electrolytic solution, which are essential for the conduction of electricity. The script discusses how the amount of solute affects the conductivity of the solution.
💡Ion
Ions are atoms or molecules that have lost or gained electrons, resulting in a net electrical charge. In the script, ions are the charge carriers in the electrolytic solution, facilitating the conduction of electricity. The concentration of ions, determined by the solute, is directly related to the solution's conductivity.
💡Mole
A mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as the number of particles (atoms, molecules, ions, etc.) in one mole, which is approximately 6.022 x 10^23. The script uses the concept of moles to relate the amount of solute in the solution to its conductivity, specifically in the calculation of molar conductivity.
Highlights

Introduction of an electrolytic cell with a power source, two plates, and an electrolytic solution.

Explanation of conduction in the solution by drawing parallels with resistance and resistivity in a metallic wire.

Derivation of the formula for conductance (G) in terms of length (L), area (a), and conductivity (Kappa).

Definition of cell constant (G Star) as the ratio of L to a for a given electrolytic cell.

Conversion of the conductance formula to incorporate the cell constant.

Discussion on the difference between resistivity and conductivity in the context of metallic wires and electrolytic cells.

Introduction of molar conductivity as a standardized measure of conductivity per mole of solute.

Explanation of the significance of molar concentration in determining the charge transfer and conductivity of a solution.

Unit conversion exercise to adapt molar conductivity for practical calculations using CGS units.

Final formula for molar conductivity in Siemens centimeter square per mole.

The importance of the common area (a) between the plates in determining the effective area for conduction.

How the effective area changes with the immersion of the plates in the electrolytic solution.

The concept that the circuit breaks when the plates are completely out of the solution.

Units of conductance and conductivity explained in terms of Siemens and Siemens per meter.

The role of solute concentration in affecting the number of ions and thus the conductivity of the solution.

Practical application of the cell constant in measuring the conductance of different solutions using the same cell.

Comparison of resistivity values for different materials to determine better conductors.

The necessity of considering the concentration of solute when comparing different solutions for conductivity.

The idea of a cube with 1 cm³ volume to standardize the measurement of conductivity per unit volume.

Introduction of the uppercase Lambda symbol for molar conductivity.

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