Question

(a) Conductance (G), conductivity (K) and molar conductivity (∧_m) are terms used in electrolytic conduction.

(i) Write any two factors on which conductivity depends on.

(ii) How do conductivity and molar conductivity vary with concentration of electrolytic solution?

(b) Write any one difference between primary cell and secondary cell.

Answer 1

(a) 

(i) 1. the nature of the electrolyte added

2. size of the ions produced and their solvation

3. the nature of the solvent and its viscosity

4. concentration of the electrolyte

5. temperature (any two factors)

(ii) Conductivity always decreases with decrease in concentration both for weak and strong electrolytes. This can be explained by the fact that the number of ions per unit volume that carry the current in a solution decreases on dilution.

Molar conductivity, ∧_m = _kV

∧_m increases with decrease in concentration. This is because the total volume (V) of the solution containing one mole of electrolyte also increases. The decrease in K on dilution is more than compensated by increase in its volume.

In the case of strong electrolytes Am increases slowly with dilution and can be represented by the equation:

Λ_m=Λ⁰_m−Ac^1/2

where ‘c’ is the molar concentration, ‘A’ is a constant (equato to -ve of slope) and ∧_m° is the limiting molar conductivity. Here, the plot of ∧_m against ‘C^1/2‘ will be a straight line. In the case of weak electrolytes ∧_m increases steeply on dilution, especially near lower concentrations due to increase in degree of dissociation.

(b) Primary cell – Cell in which the reaction occurs only once and after use over a period of time the cell becomes dead and cannot be reused again. Secondary cell – Cell which can be recharged after use by passing current through it in the opposite direction so that it can be used again.