Question

There are two solutions with the same molarity - urea and calcium chloride. Which of these solutions has higher osmotic pressure (at the same temperature). Explain your answer.​

Answer 1

The osmotic pressure of Calcium Chloride is more than the osmotic pressure of urea.

Explanation:

Osmotic pressure ($\pi$) is a colligative property that depends on the number of solute particles present in the solution.

The osmotic pressure ($\pi$) for a solution can be calculated by:

$\pi = iCRT\\i = Vant\ Hoff\ factor\\R = Gas\ Constant\\T = Temperature\\C = Concentration$

Osmotic pressure for the two solutions:

Urea: $\pi_{1} = i_{1} C_{1} RT$

Calcium Chloride: $\pi_{2} = i_{2} C_{2} RT$

Given:

$C = same\ for\ both\ solution\\R, T = Constant$

Then $\pi$ depends only on Vant Hoff Factor

$Vant\ Hoff\ factor\ for\ Urea\ i_1= 1\\Vant\ Hoff\ factor\ for\ CaCl_2\ i_2 = 3$

Because urea does not dissociate. And $CaCl_2$ dissociates into 3 ions.

Comparing:

$\pi _1 =i_1C_1RT \\\pi _2= i_2C_2RT\\\\\pi _1 = 1CRT\\\pi _2 = 3CRT$

Hence $\pi _2\ is\ greater\ then\ \pi _1$

So, Osmotic pressure of $CaCl_2$ is more than the osmotic pressure of urea.