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)
Options:
(A) 20% sucrose solution
(B) 20% NaCl solution
(C) 10% sucrose solution + 10% NaCl solution
(D) 15% sucrose solution + 5% NaCl solution
Official Answer Key:
B
Step-by-Step Solution & Explanation
• By Raoult's law, aw = n_water/(n_water + n_solute); for NaCl (an electrolyte that dissociates), the effective mole count doubles (van't Hoff factor i=2), while sucrose (non-electrolyte) does not dissociate.
• Computing aw per 100 g solution basis for each option (water = 80 g in all cases, i.e., 4.444 mol): 20% sucrose gives aw≈0.987; 20% NaCl gives aw≈0.867; 10%+10% mix gives aw≈0.923; 15%+5% mix gives aw≈0.954.
• A lower external solution water activity relative to the potato's (0.942) creates a greater osmotic driving force, removing water more efficiently. The 20% NaCl solution has the lowest water activity (≈0.867) of all four options, giving the largest activity gradient and hence the most efficient osmotic dehydration medium.
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