Question

The water activity of potato is 0.942. As per Raoult’s law, the most efficient solution for osmotic dehydration of potato is__________.
(Molar mass of sucrose = 342 g mole\(^{-1}\), and NaCl = 58.5 g mole\(^{-1}\))

• A. 20% sucrose solution
• B. 20% NaCl solution
• C. 10% sucrose solution + 10% NaCl solution
• D. 15% sucrose solution + 5% NaCl solution

Hint:

For osmotic dehydration, solutions like NaCl are more efficient because they dissociate into ions, increasing the osmotic pressure. When using Raoult’s law, consider both the concentration of solute and its dissociation.

Answer 1

The Correct Option is B

Raoult’s law is used to model the vapor pressure lowering in a solvent when a solute is added, and it is particularly useful in osmotic processes like dehydration. The water activity (\(a_w\)) is defined as the ratio of the vapor pressure of the solution to the vapor pressure of the pure solvent. In osmotic dehydration, we typically aim to reduce the water activity in the material, which can be achieved by selecting an appropriate osmotic solution. In the given problem, the water activity of potato is provided as 0.942. To find the most efficient osmotic solution for dehydrating potato, we apply Raoult’s law, which links the solute concentration to the lowering of vapor pressure. For osmotic dehydration, it is essential to select a solution that provides the most efficient osmotic pressure (i.e., lowering the water activity effectively). Sucrose and NaCl are common solutes used in osmotic dehydration. However, sodium chloride (NaCl) dissociates into two ions in solution (Na+ and Cl-), while sucrose does not dissociate. Therefore, a NaCl solution at a given concentration will produce more osmotic pressure than a sucrose solution of the same molar concentration. Given the molar masses of sucrose (342 g/mol) and NaCl (58.5 g/mol), the dissociation of NaCl into two ions makes it more effective for lowering water activity compared to sucrose. Based on this principle, the most efficient solution for osmotic dehydration of potato is a 20% NaCl solution, as it produces the highest osmotic pressure while achieving the desired water activity reduction. Thus, the correct answer is (B) 20% NaCl solution.