Question

When a certain conductivity cell was filled with 0·05 M KCl solution, it has a resistance of 100 ohm at 25ºC. When the same cell was filled with 0·02 M AgNO₃ solution, the resistance was 90 ohm. Calculate the conductivity and molar conductivity of AgNO₃ solution. (Given : Conductivity of 0·05 M KCl solution = 1·35 × 10⁻² ohm⁻¹cm⁻¹)

Batteries and fuel cells are very useful forms of galvanic cell. Any battery or cell that we use as a source of electrical energy is basically a galvanic cell. However, for a battery to be of practical use it should be reasonably light, compact and its voltage should not vary appreciably during its use. There are mainly two types of batteries — primary batteries and secondary batteries. In the primary batteries, the reaction occurs only once and after use over a period of time the battery becomes dead and cannot be reused again, whereas the secondary batteries are rechargeable. Production of electricity by thermal plants is not a very efficient method and is a major source of pollution. To solve this problem, galvanic cells are designed in such a way that energy of combustion of fuels is directly converted into electrical energy, and these are known as fuel cells. One such fuel cell was used in the Apollo space programme. Answer the following questions:

Resistance of a conductivity cell filled with 0.2 mol L⁻¹ KCl solution is 200 Ω. If the resistance of the same cell when filled with 0.05 mol L⁻¹ KCl solution is 620 Ω, calculate the conductivity and molar conductivity of 0.05 mol L⁻¹ KCl solution. The conductivity of 0.2 mol L⁻¹ KCl solution is 0.0248 S cm⁻¹.

Give reasons: (i) Mercury cell delivers a constant potential during its life time. (ii) In the experimental determination of electrolytic conductance, Direct Current (DC) is not used.