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GATE 2022 AG – Question 44

Dairy and Food Engineering · Unit Operations in Dairy and Food Engineering · 2 marks · Multiple choice

Potato water activity is .942. Using Raoult’s law, which solution is most efficient for osmotic dehydration? Molar masses: sucrose342 g/mol, NaCl58.5 g/mol.

  1. 20% sucrose
  2. 20% NaCl
  3. 10% sucrose +10% NaCl
  4. 15% sucrose +5% NaCl

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Correct answer: (B) 20% NaCl

Explanation

On a 100 g solution basis, all choices contain80 g water. At fixed solute mass, lower molar mass gives more solute particles and lowers water mole fraction further. Twenty grams NaCl supplies.34188 mol formula units versus.05848 mol sucrose; dissociation strengthens the difference. It has the lowest external water activity and greatest osmotic driving force. Thus **B**.

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