Question

if you make a solution by dissolving 1.0 mol of Fecl3 into 1 kg of water how would the osmotic pressure of this solution compare with the osmotic pressure of a solution that is made from 1.0 mol of glucose in 1 kg of water

Answer 1

The osmotic pressure is greater in the FeCl3 solution. The FeCl3 is an ionic compound, so it dissociates into Fe3+ and 3Cl-, creating 4 overall particles, while the glucose remains as 1 particle. The water increases in the FeCl3 to compensate for that added particle concentration. 

Answer 2

Explanation:

Osmotic pressure is defined as the minimum pressure which has to applied on the solution to prevent the entry of the solvent in the solution through a semi-permeable membrane.

It is a type of colligative property which means it depends on the amount of the solution. More the amount, more will be the osmotic pressure.

Mathematically,

$\pi =icRT$

$\pi$ = Osmotic pressure

i = Vant's Hoff factor which is 1 for non-electrolyte solutions

c = Concentration of solution

R = Solution constant

T = temperature

• For $FeCl_3$

As Ferric chloride is an electrolyte, so it will completely dissociate into its ions.

1 mole of ferric chloride will dissociate into 1 $Fe^{3+}$ ion and 3 $Cl^-$ ions.

$FeCl_3\rightarrow Fe^{3+}+3Cl^-$

Here, value of i = 4

• For Glucose

Glucose is a non-electrolyte and hence will not dissociate into the respective ions. So, value of i = 1

Osmotic pressure will be high for high value of 'i'. Therefore, osmotic pressure of $FeCl_3$ will be high as compared to the glucose in same amount of water.