Kidz Olympiad🎉

Science Class 12 - Electrochemistry Notes

Comprehensive study notes for Class 12 - Electrochemistry olympiad preparation

Electrochemistry

Welcome to the chapter on Electrochemistry for Class 12. In this chapter, you will learn about the chemical processes that involve the movement of electrons, the construction and working of electrochemical cells, and the quantitative aspects of electrolysis. By the end of this chapter, you will be able to explain the principles of electrochemistry and solve related numerical problems.

Key Concepts

  • Electrochemistry: The study of the relationship between electricity and chemical reactions.
  • Redox Reaction: A reaction involving the transfer of electrons between two species.
  • Electrochemical Cell: A device that converts chemical energy into electrical energy or vice versa.
  • Electrolysis: The process of using electricity to drive a non-spontaneous chemical reaction.

Electrochemical Cells

Electrochemical cells are of two types:

  • Galvanic (Voltaic) Cell: Converts chemical energy into electrical energy. Example: Daniell cell.
  • Electrolytic Cell: Uses electrical energy to drive a chemical reaction.

Example: In a Daniell cell, zinc and copper electrodes are placed in their respective salt solutions and connected by a salt bridge. Electrons flow from zinc to copper, generating electricity.

Electrode Potential

  • Electrode Potential: The tendency of an electrode to lose or gain electrons when in contact with its ion solution.
  • Standard Electrode Potential (E°): The electrode potential measured under standard conditions (1 M, 1 atm, 25°C).
  • Standard Hydrogen Electrode (SHE): Used as a reference electrode with E° = 0 V.

Nernst Equation

The Nernst equation relates the cell potential to the concentrations of the ions involved:

Ecell = E°cell - (0.0591/n) log Q

  • Ecell: Cell potential under non-standard conditions
  • E°cell: Standard cell potential
  • n: Number of electrons transferred
  • Q: Reaction quotient

Electrolysis and Faraday’s Laws

  • Electrolysis: Decomposition of a substance by passing electric current through its solution or molten state.
  • Faraday’s First Law: The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed.
  • Faraday’s Second Law: When the same quantity of electricity is passed through different electrolytes, the masses of substances deposited are proportional to their equivalent weights.

Formula: m = (E × Q) / F, where m = mass, E = equivalent weight, Q = charge, F = Faraday’s constant (96500 C/mol).

Applications of Electrochemistry

  • Batteries and fuel cells
  • Electroplating
  • Corrosion and its prevention
  • Extraction and purification of metals

Practice Questions

  1. Define standard electrode potential.
  2. Write the Nernst equation for a cell reaction involving 2 electrons.
  3. Calculate the mass of copper deposited when 2 Faradays of electricity are passed through copper(II) sulfate solution (Cu = 63.5 g/mol).
  4. What is the difference between a galvanic cell and an electrolytic cell?
  5. Explain Faraday’s first law of electrolysis with an example.

Challenge Yourself

  • Draw and label a Daniell cell. Show the direction of electron flow.
  • Explain how corrosion is an electrochemical process and suggest ways to prevent it.

Did You Know?

  • The first battery was invented by Alessandro Volta in 1800.
  • Electrochemistry is used in making rechargeable batteries for mobile phones and electric cars.

Glossary

  • Electrolyte: A substance that conducts electricity when dissolved in water or molten.
  • Electrode: A conductor through which electricity enters or leaves an electrolyte.
  • Redox Reaction: A reaction involving reduction and oxidation.
  • Faraday: The amount of electric charge carried by one mole of electrons (96500 C).

Answers to Practice Questions

  1. It is the electrode potential of an electrode measured under standard conditions (1 M, 1 atm, 25°C) relative to the standard hydrogen electrode.
  2. Ecell = E°cell - (0.0591/2) log Q
  3. Mass = (2 × 63.5) = 127 g of copper.
  4. A galvanic cell produces electricity from a spontaneous chemical reaction, while an electrolytic cell uses electricity to drive a non-spontaneous reaction.
  5. The mass of a substance deposited is directly proportional to the quantity of electricity passed. For example, passing 1 Faraday through AgNO3 solution deposits 108 g of silver.

Practice solving electrochemistry problems to master this important topic for exams and real-life applications!

Quick Navigation