Electrochemistry

Step 1: Faraday's laws of electrolysis.
According to Faraday’s laws of electrolysis, the amount of substance liberated at an electrode is directly proportional to the quantity of charge passed through the electrolyte. The equation is: where is the mass of the substance, is the molar mass, is the charge, is the Faraday constant, and is the valence of the ion. For CuSO₄, the molar mass of copper is 63.5 g, and 96500 coulombs liberates one mole of copper. Step 2: Analysis of options.
(A) 63.5 gm copper: Correct — 96500 coulombs liberates 63.5 grams of copper, which is the equivalent of one mole of copper.
(B) 31.76 gm copper: This is incorrect; 31.76 grams would correspond to half a mole of copper.
(C) 96500 gm copper: This is incorrect, as it is too large a quantity.
(D) 100 gm copper: This is incorrect, as it does not match the molar equivalent of copper.
Step 3: Conclusion.
The correct answer is (A) because 96500 coulombs liberates 63.5 grams of copper.

Step 1: Understanding the cell constant.
The cell constant of a conductivity cell is the ratio of the distance between the electrodes to the cross-sectional area of the electrodes. It is used in the equation for calculating the conductivity of the solution. Step 2: Analysis of options.
(A) : Correct — This is the definition of the cell constant.
(B) : This does not represent the correct formula for the cell constant.
(C) : This does not represent the correct formula for the cell constant.
(D) : This does not represent the correct formula for the cell constant.
Step 3: Conclusion.
The correct answer is (A) because the cell constant is given by , where is the distance between the electrodes and is the cross-sectional area.

Step 1: Understanding the theory of ionisation.
Svante Arrhenius developed the theory of ionisation in 1887, explaining that when certain substances dissolve in water, they dissociate into ions, and this dissociation is what leads to electrical conductivity. Step 2: Analysis of options.
(A) Faraday: Faraday contributed to the understanding of electrolytic processes but did not develop the theory of ionisation.
(B) Arrhenius: Correct — Arrhenius is known for developing the theory of ionisation, describing the dissociation of substances into ions in solution.
(C) Ostwald: Ostwald worked on the dissociation of weak electrolytes but is not credited with the original theory of ionisation.
(D) Rutherford: Rutherford is famous for his work on the structure of the atom, not for the theory of ionisation.
Step 3: Conclusion.
The correct answer is (B) because Svante Arrhenius developed the theory of ionisation.

Step 1: Function of a Salt Bridge.
A salt bridge is an essential component of an electrochemical cell that maintains electrical neutrality by allowing the flow of ions between the two half-cells. It connects the anode and cathode compartments of the cell.
Step 2: Importance of the Salt Bridge.
- Maintaining electrical neutrality: The salt bridge helps maintain the balance of charges in the two half-cells by allowing ions to move between them. As oxidation occurs at the anode, positive ions accumulate, and as reduction occurs at the cathode, negative ions accumulate. The salt bridge neutralizes this charge buildup by providing a pathway for ion movement. - Prevention of liquid junction potential: The salt bridge prevents the formation of a potential difference between the two solutions due to the difference in ion concentrations, which could disrupt the cell's functioning. - Facilitating ion flow: It enables the flow of ions, which is necessary to complete the circuit and allow the redox reactions to proceed.
Step 3: Materials Used.
A common salt bridge is made of a gel containing a neutral salt like potassium chloride (KCl) or sodium sulfate (Na₂SO₄).
Final Answer: The salt bridge is important in an electrochemical cell for maintaining electrical neutrality, preventing liquid junction potential, and facilitating ion flow between the two half-cells.
Final Answer:

Step 1: Electrochemical Cell.
An electrochemical cell is a device that converts chemical energy into electrical energy. It consists of two electrodes (anode and cathode) immersed in an electrolyte. The flow of electrons from the anode to the cathode through an external circuit produces electricity. - Spontaneous reaction: The reactions occurring in the electrochemical cell are spontaneous, meaning they occur naturally. - Example: Galvanic cell (e.g., Daniell cell).
Step 2: Electrolytic Cell.
An electrolytic cell is a device that converts electrical energy into chemical energy. In this cell, electrical energy is used to drive a non-spontaneous reaction, forcing ions to migrate and undergo chemical changes at the electrodes. - Non-spontaneous reaction: The reactions occurring in the electrolytic cell are non-spontaneous and require an external power source. - Example: Electrolysis of water.
Step 3: Key Differences.
- Function: Electrochemical cell generates electricity, while electrolytic cell requires electricity. - Reactions: Electrochemical cell involves spontaneous reactions, while electrolytic cell involves non-spontaneous reactions. - Energy Conversion: Electrochemical cell converts chemical energy to electrical energy, and electrolytic cell converts electrical energy to chemical energy.
Final Answer: An electrochemical cell generates electricity through spontaneous reactions, while an electrolytic cell uses electricity to drive non-spontaneous reactions.
Final Answer:

Step 1: Understand Faraday’s Second Law of Electrolysis.
Faraday’s Second Law of Electrolysis states that the amount of substance deposited or liberated at an electrode is directly proportional to the quantity of electric charge passed through the electrolyte. Mathematically, it is given as: Where: - and are the masses of the substances deposited or liberated. - and are the molar masses of the substances. - and are the electric charges passed.
Step 2: Explanation.
This law helps in understanding how different substances react when electric current is passed through an electrolyte and how much of each substance is involved in the electrolysis process.
Final Answer: Faraday’s Second Law of Electrolysis relates the amount of substance deposited or liberated to the electric charge passed.
Final Answer:

Step 1: Understand oxidation in electrolysis.
In electrolysis, oxidation is the loss of electrons, and it always occurs at the anode. The anode is the electrode where oxidation takes place, and electrons are released into the electrolyte.
Step 2: Compare the options.
- Option (A) Anode: Correct, because oxidation happens at the anode during electrolysis. - Option (B) Cathode: Incorrect, the cathode is where reduction (gain of electrons) occurs, not oxidation. - Option (C) Both anode and cathode: Incorrect, oxidation only occurs at the anode. - Option (D) Depends upon electrolyte used: Incorrect, oxidation always occurs at the anode, regardless of the electrolyte.
Final Answer:

Step 1: Apply the concept of Faraday's law.
The quantity of electricity required to liberate a specific mass of a substance during electrolysis is related to Faraday's law. The formula is:
Step 2: Calculate the moles of oxygen.
The molar mass of oxygen is 32 g, so 32 g of oxygen is equal to 1 mole of oxygen.
Step 3: Calculate the quantity of electricity.
To liberate 1 mole of oxygen, 4 moles of electrons are required (from the reaction ). Therefore, the required quantity of electricity is 2 faradays.
Final Answer:

Step 1: Define rust.
Rust is a compound that forms when iron or its alloys react with oxygen and water. It typically appears as a reddish-brown color on iron surfaces.
Step 2: Understand the composition of rust.
Rust is primarily composed of hydrated ferric oxide, a compound that forms through the reaction of iron with oxygen and moisture. This is why the correct answer is hydrated ferric oxide.
Step 3: Eliminate the incorrect options.
- Option (A) Powdered iron: Incorrect, powdered iron is just iron in a fine powdered form, not rust. - Option (B) Ferrous oxide: Incorrect, ferrous oxide is , a different compound from rust. - Option (C) Ferric oxide: Incorrect, ferric oxide is , which is a component of rust but not the hydrated form. - Option (D) Hydrated ferric oxide: Correct, this is the actual chemical composition of rust, consisting of iron oxides mixed with water molecules.
Final Answer:

Step 1: Understand the formula for electromotive force.
The electromotive force (EMF) of a galvanic cell is calculated using the standard electrode potentials of the two half-reactions. The formula is:
Step 2: Identify the cathode and anode.
- Zinc (Zn) is the anode because it has a more negative standard electrode potential and will undergo oxidation (Zn Zn + 2e ). - Iron (Fe) is the cathode because it has a less negative standard electrode potential and will undergo reduction (Fe + 2e Fe).
Step 3: Apply the electrode potentials.
- Standard electrode potential for zinc (Zn |Zn) is -0.76 V. - Standard electrode potential for iron (Fe |Fe) is -0.44 V. So, the EMF is:
Final Answer: