Question

What is the SI unit of molar conductivity?

• A. \(S\,cm^{-1}\)
• B. \(S\,cm^{2}\,mol^{-1}\)
• C. \(S\,mol^{-1}\)
• D. \(S\,cm\)

Hint:

Important conductivity units:
• Conductivity \((\kappa)\): \(S\,cm^{-1}\)
• Molar conductivity \((\Lambda_m)\): \(S\,cm^{2}\,mol^{-1}\) Molar conductivity increases as dilution increases.

Answer 1

The Correct Option is B

Topic: Electrochemistry - Molar Conductivity
Step 1: Understanding the Question:
The question asks for the standard unit used to measure the conductivity of an electrolyte per unit of its molar concentration.
Step 2: Key Formula or Approach:
Molar conductivity (\(\Lambda_m\)) is defined by the formula:
\[ \Lambda_m = \frac{\kappa}{C} \]
where \(\kappa\) is conductivity and \(C\) is molar concentration.
Step 3: Detailed Explanation:
1. Unit of Conductivity (\(\kappa\)): \(S \, \text{cm}^{-1}\) (Siemens per centimeter).
2. Unit of Concentration (\(C\)): \(mol \, \text{cm}^{-3}\) (Moles per cubic centimeter).
3. Combine the units:
\[ \text{Unit} = \frac{S \cdot \text{cm}^{-1}}{mol \cdot \text{cm}^{-3}} = S \cdot \text{cm}^{-1} \cdot \text{cm}^3 \cdot mol^{-1} \]
\[ \text{Unit} = S \cdot \text{cm}^2 \cdot mol^{-1} \]
Step 4: Final Answer:
The SI unit (commonly used in this form in chemistry) is \(S \, \text{cm}^2 \, mol^{-1}\).