Which of the following solutions of equal concentration will have a 2-fold higher osmotic pressure than that of a sucrose solution of the same concentration?

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Multiple Choice

Which of the following solutions of equal concentration will have a 2-fold higher osmotic pressure than that of a sucrose solution of the same concentration?

Osmotic pressure scales with the number of solute particles in solution. For dilute solutions, π = i M R T, where i is the van't Hoff factor (how many particles the solute produces). Sucrose doesn’t dissociate, so i ≈ 1. Potassium chloride dissociates into two ions (K+ and Cl−), giving i ≈ 2. At the same molar concentration, this yields about twice the osmotic pressure of a sucrose solution. The other salts produce more particles per formula unit (K2SO4 → 3 ions, AlCl3 → 4 ions, K3PO4 → 4 ions), leading to higher than a twofold increase. Under ideal behavior, potassium chloride best matches the requested twofold rise.

Osmotic pressure scales with the number of solute particles in solution. For dilute solutions, π = i M R T, where i is the van't Hoff factor (how many particles the solute produces). Sucrose doesn’t dissociate, so i ≈ 1. Potassium chloride dissociates into two ions (K+ and Cl−), giving i ≈ 2. At the same molar concentration, this yields about twice the osmotic pressure of a sucrose solution. The other salts produce more particles per formula unit (K2SO4 → 3 ions, AlCl3 → 4 ions, K3PO4 → 4 ions), leading to higher than a twofold increase. Under ideal behavior, potassium chloride best matches the requested twofold rise.

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