Question

(i) Write the cell reaction and Nernst equation for a Daniel cell. 
(ii) Explain the variation of conductivity and molar conductivity of a solution with dilution.

• A.
• B.
• C.
• D.

Hint:

Key Points:

1. Daniell cell reaction:
Zn + Cu2+ → Zn2+ + Cu

2. Nernst equation:
E = E° − (0.0591 / n) log Q

3. Conductivity decreases with dilution.

4. Molar conductivity increases with dilution.

Answer 1

The Correct Option is A

Concept:
A Daniell cell is a galvanic cell in which chemical energy is converted into electrical energy through a redox reaction between zinc and copper ions. The Nernst equation helps determine the cell potential under non-standard conditions. Conductivity and molar conductivity describe how well an electrolyte solution conducts electricity and how they change with dilution.

Step 1: Daniell Cell Reaction and Nernst Equation.
A Daniell cell consists of a zinc electrode in ZnSO4 solution and a copper electrode in CuSO4 solution.

Anode (Oxidation):
Zn(s) → Zn2+(aq) + 2e−

Cathode (Reduction):
Cu2+(aq) + 2e− → Cu(s)

Overall Cell Reaction:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

The Nernst equation for the Daniell cell at 298 K is:
Ecell = E°cell − (0.0591 / 2) log([Zn2+] / [Cu2+])

Step 2: Variation of Conductivity and Molar Conductivity with Dilution.

Conductivity (κ):
It is the conductance of ions present in a unit volume of solution. When a solution is diluted, the number of ions per unit volume decreases; therefore conductivity decreases.

Molar Conductivity (Λm):
It is defined as the conductance of all the ions produced by one mole of electrolyte in solution.
Λm = (κ × 1000) / C

On dilution, ions move more freely and the volume containing one mole of electrolyte increases. Hence, molar conductivity increases with dilution.