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: Understand the question.
We must pick the salt solution used in a conductivity cell to find the cell constant.

Step 2: Recall what cell constant means.
The cell constant is the distance between the electrodes divided by their area, $b = l/A$. We cannot measure this directly inside a sealed cell.

Step 3: See how it is found indirectly.
We use a standard solution whose conductivity $\kappa$ is already known accurately. We measure its resistance $R$ and then use:
\[ b = \kappa \times R \]

Step 4: Note what the standard must be.
The standard solution must be very pure, stable, not easily changed by water, and must have well known conductivity at many concentrations and temperatures.

Step 5: Identify the standard.
Potassium chloride (KCl) fits all these needs and is the one recommended for this calibration. The other salts are not used as the standard here.

Step 6: Pick the answer.
The salt used is KCl, which is option 3.
\[ \boxed{\text{KCl}} \]