Question

The following solutions are prepared by dissolving the requisite amount of solute in water to obtain the desired concentrations. Rank the solutions according to their respective osmotic pressures in decreasing order assuming the complete dissociation of ionic compounds. Rank from highest to lowest osmotic pressure. To rank items as equivalent, overlap them. (a) 1 M MgCl2 (b) 1 M KCI(c) 1 M C12H22011

Answer 1

Answer: $MgCl_{2}$ > $KCl$  > $C_{12}H_{22}O_{11}$

Explanation:

Osmotic pressure is a colligative property which depends on the amount of solute added.

$\pi=iCRT$

$\pi$ = osmotic pressure

i= vant hoff factor

C= concentration in Molarity

R= solution constant

T= temperature in Kelvin

1.. For $MgCl_{2}$

, i= 3 as it is a electrolyte and dissociate to give 3 ions.

$MgCl_2\rightarrow Mg^{2+}+2Cl^{-}$  

2. For $KCl$

, i= 2 as it is a electrolyte and dissociate to give 2 ions.

$KCl\rightarrow K^{+}+Cl^{-}$  

3. For $C_{12}H_{22}O_{11}$

, i= 1 as it is a non electrolyte and does not dissociate.

Thus as vant hoff factor is highest for $MgCl_{2}$ , the osmotic pressure will be highest.

The order from highest to lowest osmotic pressure will be : $MgCl_{2}$,   $KCl$  and $C_{12}H_{22}O_{11}$