Question

The one which decreases with dilution is:
A. Molar conductance
B. Conductance
C. Specific conductivity
D. None of these

Answer 1

Hint: It is the reciprocal of specific resistance. We can also calculate this by the product of cell constant and conductance. And the unit of it is seimen per centimetre.

Complete step by step answer:

As we know that, conductance of ions is due to the presence of ions in the solution. The greater the number of ions, the greater is the conductance. As with dilution, more ions are produced in solution so conductance increases on dilution.
Molar conductivity also increases with dilution as it depends on the product of conductivity (k) and the volume (V) of solution containing one mole of electrolyte.
˄ = k × V
On dilution, specific conductivity decreases. Upon diluting the solution, the concentration of ions per centimetre cube decreases and therefore, the specific conductivity decreases but molar conductivity increases. As we increase the dilution, volume containing one mole of electrolyte increases. This increase in volume on dilution is much more than a decrease in specific conductivity. As a result, molar conductivity increases with dilution. The molar conductance of strong (HCl, KCl,\[KN{{O}_{3}}\]) as well as weak electrolytes (\[C{{H}_{3}}COOH\]) increase with decrease in concentration or increase in dilution.
So, our correct answer is option C. Specific conductivity decreases with increase in dilution.

Note: We should know more about molar conductance. In concentrated solutions of strong electrolytes there are strong forces of attraction between the ions of opposite charges called interionic forces. Due to these interionic forces the conducting ability of the ions is less in concentrated solutions. With dilution, the ions become far apart from one another and interionic forces decrease. As a result, molar conductivity increases with dilution.