Question

Moisture contained by a substance that exerts equilibrium vapour pressure less than that of liquid at same temperature is known as

• A. Equilibrium moisture
• B. Bound moisture
• C. Unbound moisture
• D. Free moisture

Hint:

Bound moisture $\implies p < p_0$ ($a_w < 1.0$).
Unbound moisture $\implies p = p_0$ ($a_w = 1.0$).
Free moisture = Total moisture $-$ Equilibrium moisture.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Moisture held within biological and agricultural materials is classified by its physical-chemical binding energy and equilibrium vapour pressure.
Key Formula or Approach:
\[ \text{Water Activity } (a_w) = \frac{p}{p_0} < 1.0 \quad \text{(for bound moisture)} \]

Step 2: Detailed Explanation:
1. Bound Moisture: Water held firmly within plant tissue cells by strong chemical, capillary, or hydrogen bonds. It exerts an equilibrium vapour pressure \(p\) strictly less than the saturation vapour pressure of pure water \(p_0\) at the same temperature (\(a_w < 1.0\)).
2. Unbound Moisture: Free capillary or surface moisture exerting the full saturation vapour pressure of pure water (\(p = p_0\), \(a_w = 1.0\)).
3. Free Moisture: Moisture in excess of the equilibrium moisture content for given drying conditions.

Step 3: Final Answer:
Thus, moisture exerting vapour pressure less than pure liquid at that temperature is Bound moisture, corresponding to option (B).