Question

Consider the solutions, 0.04 m urea [(NH_2)_2C=O)], 0.04 m AgNO_3 and 0.04 m CaCl_2. Which has

(i) the highest osmotic pressure(ii) the highest vapor pressure, (iii) the highest boiling point?
a. all will be the same.

b (a) 0.04 m CaCl_2 (b) 0.04 m urea (c) 0.04 m urea.
c. (a) 0.04 m CaCl_2 (b) 0.04 m urea (c) 0.04 m CaCl_2.
d. (a) 0.04 m urea (b) 0.04 m CaCl2 (c) 0.04 m urea.
e. (a) 0.04 m CaCl_2 (b) 0.04 m CaCl_2 (c) 0.04 m CaCl_2.

Answer 1

Step-by-step explanation:

All the colligatives properties are modified by the Van't Hoff factor. This is shown as i, in the formula of the colligative properties freezing point depression, boiling point elevation, and osmotic pressure.

The Van't Hoff factor shows the number of particles into which the solute dissociates. In organic compounds we use 1, in inorganic compounds we have to think the dissociation. For example in aquous solutions, inorganic salts as AgNO₃ and CaCl₂ dissociate like this:

AgNO₃ → Ag⁺ + NO₃⁻

CaCl₂ → Ca²⁺ + 2Cl⁻

AgNO₃ has 2 moles of ions and CaCl₂ has 3 moles.

In urea: i = 1

In silver nitrate: i = 2

In calcium chloride: i = 3

The i = 3 for calcium chloride, makes that this salt has the highest osmotic pressure, highest vapor pressure and highest boiling point.