Class 12 Chemistry Important Questions on Electrochemistry

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Electrochemistry Very Short Answer Type Questions- 1M

  1. What is meant by standard electrode potential?
    Answer: Standard electrode potential (E°) of a half cell is the potential difference when one electrode is dipped in molar solution of its ion at 298 K. If electrode is gaseous the pressure of gas must be one atmosphere. In IUPAC system, reduction potential are known as standard electrode potential.

2. Write Ohm’s law.
Answer:
According to Ohm’s law, “It states that potential difference across the conductor is directly proportional to the current (I) flowing through it” i.e.,
Mathematically, it can be written as:
I ∝ V
V = IR (R = Resistance, unit = ohm, Q)

3.What is cell constant?
Answer: For a conductivity cell, the ratio of distance between two electrodes (l) and area of cross-section of electrode (A) is called as cell constant.
Cell constant = 1A or x = 1A
Unit of cell constant = cm-1

4. Write the unit of specific conductance.
Answer:
ohm-1metre-1= Ω-1m-1 = Sm-1

Electrochemistry Short Answer Type Questions- 2M

1. What is salt bridge ? Write its two functions.
Answer:
‘U’ shaped tube filled with KCl or KNO3 in Agar – Agar solution or gelatin, is known as salt bridge. It connects the two half cell.

Functions:

  1. It allows the flow of current by completing the circuit.
  2. It maintains the electrical neutrality.

2.What is specific conductance? Give its unit.
Answer:
Specific conductivity:
The reciprocal of resistivity is called specific conductivity. It is defined as the conductance between the opposite faces of one centimeter cube of a conductor. It is denoted by K (kappa).
Thus.
K = 1ρ (∵ ρ = RAl
K = 1R × 1A
where, R = Resistance, A = Cross – sectional area of electrodes and l = Length between the electrodes.
Unit = K = 1ohm × cmcm2 = ohm-1 cm-1
S.I. Unit Scm-1. or Ohm-1 cm-1.

3. What is equivalent conductance?
Answer:
Equivalent conductance:
“Conductance of total ion produced by one gram equivalent of electrolyte in the solution is called equivalent conductance.” It is denoted by Λeq.What is equivalent conductance?

4.What is molar conductance?
Answer:
Molar Conductivity:
The molar conductivity of a solution at definite concentration of (or dilution) and temperature is the conductivity of that volume which contains one mole of the solute and is placed between two parallel electrodes 1 cm apart and having sufficient area to hold whole of the solution. It is denoted by Λm.
Mathematically,
Λ m=k × V .. (1)
Where, V is the volume in ml in which one gram mole of substance is dissolved.
If M is molarity or m moles are dissolved in 1000 ml.

What is molar conductance

 

 

Write difference between Metallic conduction and Electrolytic conduction.

Metallic conduction:Electrolytic conduction:
Metallic conduction takes place by movement of electrons.Electrolytic conduction takes place by movement of ions.
There is no chemical change.Due to chemical change decomposition of electrolyte takes place.
There is no transfer of matter.Transfer of matter takes place as ions.
In metallic conduction conductivity decreases with increase in temperature.In electrolytic conduction conductivity
increases with increase in temperature.

What are the difference between emf (Cell potential) and potential difference:

EMF (Cell potential):Potential difference:
It is the potential difference between the two terminals of the cell when no current is flowing in the circuit, i.e., in an open circuit.It is the difference of the electrodes potentials of the two electrodes when the cell is sending current through the circuit.
It is the maximum voltage which can be obtained from a cell.It is the less than the maximum voltage as it is the difference of electrode potential.
It can be measured by potentiaometrie method.It can be measured by simple voltmeter also.
Work performed by electromotive force is the maximum work done by a cell.Work performed by potential difference is less than the maximum work done by a cell.
It is responsible for continuous flow of current in electric circuit.It is not responsible for the continuous flow of current in circuit.

Differentiate between Electrochemical cell (Galvanic cell) and Electrolytic cell.

Electrochemical cell:Electrolytic cell:
It is a device to convert chemical energy into electrical energy.It is a device to convert electrical energy into chemical energy.
It consists of two electrodes in different compartments joined by a salt bridge.Both the electrodes are in same solution.
Redox reactions occurring in the cell are spontaneous.Redox reactions occurring in the cell are non – spontaneous.
Free energy decreases with operation of cell, i.e., ∆G <0.Free energy increases with operation of cell, i.e., ∆G >0.
Useful work is obtained from the cell.Work is done on the system.
Anode works as negative and cathode as positive electrodes.Anode is positive and cathode is negative.
Electrons released by oxidation process at anode go into external circuit and pass to cathode.Electrons enter into cathode electrode from external source and leave the cell at anode.
To set – up this cell, a salt bridge/porous pot is used.No salt bridge is used in this cell.

Electrochemistry Long Answer Type Questions- 3 and 5M


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