Question

Consider two solutions made using water as the solvent: 1.0 m CaCl2 and 3.0 m sucrose. Describe how the osmotic pressures of these two solutions compare. Explain why this is true.

Answer 1

The osmotic pressures of the two solutions are the same.

Both solutions contain the same number of dissolved particles in the same quantity of the same solvent.

Osmotic pressure is a colligative property.

Because it is a colligative property, osmotic pressure is influenced only by the number of dissolved particles, not by the identities of the particles.

Answer 2

Osmotic pressure is calculated by the product of the concentration in molarity, the temperature, the vant Hoff factor (3 for CaCl2 and 1 for sucrose) and R, universal gas constant. At the same temperature, the osmotic pressures of both solutions are equal.

π = CRTi
For CaCl2,
π = (1)RT(3) = 3RT

For sucrose,
π = (3)RT(1) = 3RT