Question

The boiling temperature of a concentrated solution as compared to water at the same pressure would be

• A. Same
• B. Lower
• C. Higher
• D. Variable

Hint:

Colligative Properties: The boiling temperature of a concentrated dairy solution is always HIGHER than that of pure water at the same pressure (Boiling Point Elevation, BPE).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Colligative properties and Boiling Point Elevation: dissolving non-volatile milk solutes (lactose, soluble mineral salts, whey proteins) depresses the solvent chemical potential and vapor pressure according to Raoult's law, requiring higher thermodynamic temperature to reach boiling (Boiling Point Elevation BPE).
Key Formula or Approach:
\[ \mathbf{\Delta T_b} = T_{\text{boiling, solution}} - T_{\text{boiling, water}} = \mathbf{i \cdot K_b \cdot m > 0} \implies \mathbf{T_{\text{solution}} > T_{\text{water}}} \]

Step 2: Detailed Explanation:
In physical chemistry, colligative properties, and evaporator thermodynamics:
- According to Raoult's Law:
1. When non-volatile solutes (such as lactose, mineral salts, and milk proteins in concentrated skim milk, whey, or sweetened condensed milk) are dissolved in water, the equilibrium vapor pressure of the solution is depressed below that of pure water at the same temperature.
2. Boiling occurs only when solution vapor pressure equals external system pressure.
3. Consequently, the solution must be heated to a Higher Temperature (C) to achieve a vapor pressure equal to the ambient pressure.
- This phenomenon is termed Boiling Point Elevation (BPE Dühring's Rule), and for $50\%$ concentrated skim milk at atmospheric pressure, BPE is approximately $1.5^\circ - 2.5^\circ ext{C}$ higher than pure water.

Step 3: Final Answer:
Hence, the boiling temperature of a concentrated solution is Higher, matching option (C).