Question

In distillation, relative volatility is a measure of:

• A. Heat transfer rate
• B. Ease of separation of components
• C. Vapor pressure of a mixture
• D. Column efficiency

Hint:

The number of theoretical stages required for a separation is inversely related to relative volatility.
High \( \alpha \implies \) Fewer stages required.
Low \( \alpha \) (close to 1) \( \implies \) More stages required.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Distillation is a process used to separate components of a liquid mixture based on differences in their boiling points (volatilities).
Relative volatility \( (\alpha) \) is a comparison of the vapor pressures of the components in the mixture.
Step 2: Key Formula or Approach:
Relative volatility of component A with respect to component B is defined as:
\[ \alpha_{AB} = \frac{y_A / x_A}{y_B / x_B} \]
Where \( y \) is the mole fraction in vapor and \( x \) is the mole fraction in liquid.
For ideal systems, it can also be expressed as the ratio of vapor pressures:
\[ \alpha_{AB} = \frac{P_A^\circ}{P_B^\circ} \]
Step 3: Detailed Explanation:
- If \( \alpha = 1 \), the components have the same volatility, and they cannot be separated by simple distillation.
- If \( \alpha>1 \), component A is more volatile than B.
- The larger the value of \( \alpha \), the greater the difference in boiling points and the easier it is to separate the two components.
Thus, relative volatility acts as a direct indicator of how easily a separation can be achieved in a distillation column.
Step 4: Final Answer:
Relative volatility is a measure of the ease of separation of components.