Question

Which among the following aqueous salt solution is used in conductivity cell to determine cell constant?

• A. $\text{AgNO}_3$
• B. $\text{ZnSO}_4$
• C. KCl
• D. $\text{CuSO}_4$

Hint:

Whenever a laboratory protocol requires calibration of an electrochemical conductivity bridge or cell constant verification, an aqueous solution of potassium chloride (KCl) is the universal standard reagent utilized worldwide.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the standard reference electrolyte solution used internationally inside a conductivity cell to evaluate its cell constant ($b$).

Step 2: Detailed Explanation:
The cell constant of an electrochemical setup is defined as the ratio of the distance between the electrodes to their cross-sectional area ($b = \frac{l}{A}$). Since measuring physical distances directly inside a sealed glass assembly is difficult, it is determined indirectly.
To do this, we measure the electrical resistance ($R$) of a highly stable standard reference solution whose exact electrolytic conductivity ($\kappa$) is already known with exceptional precision across various temperatures.
The fundamental relation used is:
$$ b = \kappa \times R $$ Potassium chloride (KCl) solutions are universally preferred and recommended by IUPAC for this calibration because KCl can be obtained in highly pure states, is chemically stable, does not readily hydrolyze, and its specific conductivity values have been mapped with extreme accuracy across a wide range of concentrations and temperatures.

Step 3: Final Answer: The standard aqueous salt choice is KCl, which corresponds directly to option (C).