Wednesday, 19 December 2018

CBSE Class 12 - Chemistry Chapter 3 - Electrochemistry - Very Short Questions and Answers (#cbsenotes)(#eduvictors)


Short Questions and Answers 

CBSE Class 12 - Chemistry Chapter 3 - Electrochemistry - Very Short Questions and Answers (#cbsenotes)(#eduvictors)

Q1: Define electrochemistry.

Answer: Electrochemistry is the study of the production of electricity from the energy released during a spontaneous chemical reaction and the use of electrical energy to bring about non-spontaneous chemical transformations.

Q2: What is the effect of temperature on molar conductivity?

Answer: Molar conductivity of an electrolyte increases with increase in temperature.

Q3: Why is it not possible to measure single electrode potential?

Answer: Because the half-cell containing single electrode cannot exist independently, as the charge cannot ow on its own in a single electrode.

Q4: Name the types of cells.

1. Electrochemical cell (Galvanic or Voltaic cell)
2. Electrolytic cell

Q5: Name the factor on which emf of a cell depends.

Answer: Emf of a cell depends on the following factors:
(a) Nature of reactants
(b) The concentration of solution in two half cells
(c) Temperature

Q6: What is Galvanic or Voltaic cell?

Answer: It is an electrochemical cell that converts chemical energy into electrical energy.

Q7: Define Electrolytic cell

Answer: It is a device which converts electrical energy into chemical energy.

Q8: What is Limiting molar conductivity?

Answer: When concentration approaches zero i.e. at infinite dilution, the molar conductivity is known as limiting molar conductivity (Λ° m ).

Q9: What is the effect of temperature on the electrical conductance of electrolyte?

Answer: Temperature increases, electrical conductance increases.

Q10: Why does a dry cell become dead even if it has not been used for a long time?

Answer: NH₄Cl is acidic in nature. It corrodes zinc container.

Q11: Write the overall reaction taking place in rusting.

Answer: 2Fe + O₂ + 4H⁺  -------> 2Fe²⁺ + 2H₂O

Q12: Why Na cannot be obtained by the electrolysis of aqueous NaCl solution?

Answer: Due to low reduction potential, Na⁺ ions are not reduced at the cathode. Instead, H⁺ is reduced and H₂ is obtained.

Q13: Define electrolysis. 

Answer: It is the process of decomposition of an electrolyte by passing electricity through its aqueous solution or molten state.

Q14: What is the necessity to use a salt bridge in a Galvanic cell?

Answer: The salt bridge allows the movement of ions from one solution to the other without mixing of the two solutions. Moreover, it helps to maintain the electrical neutrality of the solutions in the two half cells.

Q15: How much charge is required for the reduction of 1 mol of Zn to Zn²⁺?

Answer: Zn²⁺(aq) + 2e⁻ -------> Zn(s)
1mol       2mol

One mole of Zn requires 2 moles of electrons for reduction i.e.
Q = 2 × F = 2 × 96500 = 193000 C

Q16: What is the use of platinum foil in the hydrogen electrode?

Answer: It is used for the inflow and outflow of electrons.

Q17: Why does mercury cell give a constant voltage throughout its life?

Answer: This is because the overall cell reaction does not have any ionic can concentration in it.

Q18: Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

Answer: Methane and methanol.

Q19: Out of zinc and tin, which one protects iron better even after cracks and why?

Answer: Zinc protects better because oxidation of zinc is greater but that of tin is less than that of iron.

Q20: What is the EMF of the cell when the cell reaction attains equilibrium?

Answer: Zero.

Q21: Define conductivity.

Answer: Conductivity is defined as the ease with which current flows through the electrolyte. It is reciprocal of specific resistance.

Q22: Define molar conductivity.

Answer: Molar conductivity is conductance of all the ions produced by one mole of electrolyte when electrodes are at a unit distance apart and have sufficient area of a cross-section to hold the electrolyte.

Q23: Why does the cell potential of mercury cell remain constant throughout its life?

Answer: This is because the overall cell reaction does not involve any ion in the solution whose concentration changes during its lifetime.

Q24: What are secondary batteries? 

Answer: The batteries which can be recharged again and again are called as secondary batteries. e.g., lead storage battery.

Q25: Define electrochemical series.

Answer: The arrangement of various electrodes in the decreasing or increasing order of their standard reduction potentials is called electrochemical series.