1. Explain the electronic concept of oxidation and reduction.
Answer: Oxidation involves the loss of electrons, while reduction involves the gain of electrons. In a redox reaction, one species is oxidized (loses electrons) while another is reduced (gains electrons).
2. Describe the process of assigning oxidation numbers in redox reactions.
Answer: Oxidation numbers are assigned to atoms in a compound or ion to indicate the hypothetical charge that would result if all the bonds to atoms of different elements were 100% ionic. Rules for assigning oxidation numbers include: (1) the oxidation number of an atom in its elemental form is zero, (2) the oxidation number of a monatomic ion is equal to its charge, and (3) the sum of oxidation numbers in a neutral compound is zero.
3. Explain the rules for balancing redox reactions.
Answer: The rules for balancing redox reactions include: (1) Write down the unbalanced equation, (2) Assign oxidation numbers to all elements, (3) Write half-reactions for oxidation and reduction, (4) Balance the number of atoms of each element in each half-reaction, (5) Balance the charge in each half-reaction by adding electrons, and (6) Multiply the half-reactions to equalize the number of electrons transferred and combine them to form the balanced redox equation.
4. Discuss electrolytic and metallic conduction.
Answer: Electrolytic conduction occurs in electrolyte solutions where ions migrate towards oppositely charged electrodes, carrying electric current. Metallic conduction occurs in metals where electrons are free to move and carry electric current.
5. Explain conductance and its variation with concentration in electrolytic solutions.
Answer: Conductance is the reciprocal of resistance and measures the ability of a solution to conduct electricity. Molar conductivities vary with concentration according to Kohlrausch’s Law, which states that the molar conductivity of an electrolyte at infinite dilution is the sum of the contributions of its ions.
6. What is Kohlrausch’s Law and how is it applied?
Answer: Kohlrausch’s Law states that the molar conductivity of an electrolyte at infinite dilution is the sum of the contributions of its ions. It is applied to determine the limiting molar conductivity of electrolytes and to calculate the degree of dissociation of weak electrolytes.
7. Describe electrochemical cells and their types.
Answer: Electrochemical cells are devices that convert chemical energy into electrical energy or vice versa through redox reactions. Types of electrochemical cells include electrolytic cells (where non-spontaneous reactions are driven by an external voltage) and galvanic cells (where spontaneous reactions produce electrical energy).
8. Differentiate between electrolytic and galvanic cells.
Answer: Electrolytic cells use electrical energy to drive non-spontaneous reactions, while galvanic cells produce electrical energy from spontaneous reactions.
9. Explain different potentials in electrochemical cells, including types of electrodes.
Answer: Different potentials in electrochemical cells include standard electrode potential (the potential of an electrode relative to a standard hydrogen electrode) and cell potential (the potential difference between the two electrodes in a cell). Electrodes can be inert (e.g., platinum) or active (e.g., metals participating in the redox reaction).
10. Define electrode potential and explain how it is measured.
Answer: Electrode potential is the electromotive force of an electrode in an electrochemical cell. It is measured using a voltmeter connected to the electrodes of the cell, with one electrode acting as the reference electrode (usually the standard hydrogen electrode).
11. Discuss cell reactions and EMF of a galvanic cell.
Answer: Cell reactions in a galvanic cell involve oxidation at the anode and reduction at the cathode. The EMF (electromotive force) of a galvanic cell is the maximum potential difference between the two electrodes when no current is flowing.
12. Explain the Nernst equation and its significance in electrochemistry.
Answer: The Nernst equation relates the standard electrode potential, temperature, and concentration of reactants and products in an electrochemical cell. It is used to calculate the cell potential under non-standard conditions.
13. Define standard electrode potential and Gibbs’ energy change in electrochemical cells.
Answer: Standard electrode potential is the potential of an electrode relative to a standard hydrogen electrode under standard conditions. Gibbs’ energy change (∆G°) is the maximum amount of work that can be obtained from a reaction at constant temperature and pressure.
14. Discuss the application of electrochemical cells in batteries.
Answer: Electrochemical cells are used in batteries to store and supply electrical energy. Examples include lead-acid batteries (used in cars), lithium-ion batteries (used in portable electronic devices), and nickel-metal hydride batteries (used in hybrid vehicles).
15. Explain the operation of a voltaic cell.
Answer: A voltaic cell, also known as a galvanic cell, converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two half-cells connected by a salt bridge, with oxidation occurring at the anode and reduction at the cathode.
16. Describe the functioning of an electrolytic cell.
Answer: An electrolytic cell uses electrical energy to drive non-spontaneous redox reactions, causing ions to migrate towards oppositely charged electrodes. It consists of an electrolyte solution and two electrodes connected to an external power source.
17. Explain the working principle of a lead-acid accumulator.
Answer: In a lead-acid accumulator (lead-acid battery), the anode is composed of lead (Pb) and the cathode is composed of lead dioxide (PbO2), immersed in a sulfuric acid (H2SO4) electrolyte. During discharge, lead and lead dioxide react with sulfuric acid to produce lead sulfate (PbSO4) and water, releasing electrical energy. During charging, the process is reversed.
18. Discuss the operation of fuel cells.
Answer: Fuel cells convert chemical energy directly into electrical energy through the reaction of a fuel (such as hydrogen) with an oxidizing agent (such as oxygen) at the anode and cathode, respectively. The most common type is the hydrogen fuel cell, which produces water as a byproduct.
19. Explain the significance of conductance and molar conductivity in electrochemistry.
Answer: Conductance and molar conductivity are important parameters in electrochemistry as they measure the ability of a solution to conduct electricity and provide insights into the degree of dissociation of electrolytes and their ionic mobility in solution.
20. Discuss the variations in molar conductivities with concentration and their implications.
Answer: Molar conductivities vary with concentration according to Kohlrausch’s Law, decreasing as concentration increases due to increased ion-ion interactions. This variation has implications for the conductivity and behavior of electrolyte solutions at different concentrations.