Redox and Electrochemical Concepts: Easy Explanation

Q.1: Understand oxidation and reduction in terms of electron transfer concept

Oxidation: Oxidation is the process where an atom or ion loses electrons. Example: In the reaction where magnesium reacts with oxygen (Mg → Mg²⁺ + 2e⁻), magnesium is oxidized because it loses two electrons.

Reduction: Reduction is the process where an atom or ion gains electrons. Example: In the reaction where copper ions react with electrons (Cu²⁺ + 2e⁻ → Cu), copper is reduced because it gains two electrons.

Q.2: Calculate oxidation number (ON) of an atom in a molecule or ion

Oxidation Number (ON): It is the charge an atom would have if the compound was purely ionic. Some basic rules:

• The oxidation number of an element in its pure form (e.g., O₂, N₂) is zero.
• The oxidation number of oxygen is usually -2, except in peroxides where it’s -1.
• The oxidation number of hydrogen is +1 when bonded with non-metals and -1 when bonded with metals.

Example: In H₂O, oxygen is -2, and hydrogen is +1. The sum of oxidation numbers should be zero. (2 × +1) + (-2) = 0.

Q.3: Balance the chemical equation for redox reactions

To balance a redox reaction, we use the half-reaction method:

1. Separate the oxidation and reduction half-reactions.
2. Balance all elements except oxygen and hydrogen.
3. Balance oxygen by adding H₂O molecules.
4. Balance hydrogen by adding H⁺ ions.
5. Balance the charges by adding electrons.

Q.4: Explain electrolytic conduction, conductance, and molar conductivity

Electrolytic conduction: The process by which electricity is conducted through a solution of an electrolyte. This happens because ions are free to move and carry charge.

Conductance (G): The ability of a solution to conduct electricity. It depends on the concentration of ions and their mobility.

Molar conductivity (Λ): It is the conductivity of a solution divided by its molar concentration. It shows how well a single ion can conduct electricity in a solution.

Q.5: Describe the effect of dilution on conductivity and molar conductivity of an electrolyte

Conductivity decreases with dilution: As we dilute the solution, the number of ions per unit volume decreases, which reduces the ability to conduct electricity.

Molar conductivity increases with dilution: When diluted, the ions become more spread out, reducing ion-ion interactions, so each ion can move more freely, increasing its molar conductivity.

Q.6: Differentiate between electrolytic and Galvanic cell

Electrolytic Cell: A cell that uses electrical energy to drive a non-spontaneous reaction. It requires an external power source.

Galvanic Cell: A cell that generates electrical energy from a spontaneous chemical reaction (e.g., batteries).

Q.7: State Faraday’s laws of electrolysis

First Law: The amount of substance deposited or dissolved at an electrode is directly proportional to the quantity of electricity passed.
Formula: m = Z × I × t (where m = mass of substance, Z = electrochemical equivalent, I = current, t = time)

Second Law: The amounts of different substances deposited or dissolved by the same quantity of electricity are proportional to their equivalent masses.

Q.8: Predict and justify the products of electrolysis of some common electrolytes

Example 1: Electrolysis of water (H₂O):

• At the cathode: reduction of H₂O → H₂ (hydrogen gas).
• At the anode: oxidation of H₂O → O₂ (oxygen gas).

Example 2: Electrolysis of NaCl:

• At the cathode: reduction of Na⁺ → Na (sodium metal).
• At the anode: oxidation of Cl⁻ → Cl₂ (chlorine gas).

Q.9: State standard electrode potential and use it for calculation of standard electrode potential of a cell

Standard Electrode Potential (E°): is the voltage associated with a half-reaction at standard conditions (25°C, 1 M concentration, 1 atm pressure).

The cell potential of a galvanic cell is calculated by the difference between the reduction potentials of the two electrodes:
Formula: E_cell = E_cathode – E_anode

Q.10: Explain Standard Hydrogen Electrode (SHE)

SHE is a reference electrode used to measure electrode potentials. It is based on the half-reaction: 2H⁺ + 2e⁻ → H₂

Its potential is defined as 0 volts under standard conditions.

Q.11: Describe electrochemical series and its application

The electrochemical series is a list of standard electrode potentials arranged in order of increasing reduction potential.

Application: It helps in predicting the direction of electron flow in a redox reaction and determining which substance will be oxidized or reduced.

Q.12: State the effect of concentration on electrode potential (Nernst equation)

Nernst Equation: It relates the concentration of ions to the electrode potential. E = E° – (0.0591 / n) log ([Red] / [Ox])

As the concentration of reactants increases, the potential becomes more positive, favoring reduction. As the concentration of products increases, the potential becomes more negative, favoring oxidation.

Q.13: Solve numericals based on Nernst equation

You can use the Nernst equation to calculate the potential for any redox half-reaction by substituting the values for concentrations of the reactants and products. Example: For the reaction Cu²⁺ + 2e⁻ → Cu, if the concentration of Cu²⁺ is 0.1 M and Cu is solid, then: Formula: E = E° – (0.0591 / n) log ([Cu²⁺] / [Cu]) By substituting values, you can calculate the potential.

Q.14: Find relationship between emf and Gibbs energy change

The relationship between emf (electromotive force) and Gibbs free energy change (ΔG) is given by: ΔG = -nFE_cell

Where n is the number of electrons, F is Faraday’s constant, and E_cell is the cell potential.