The increasing order of osmotic pressure of 0.1 M aqueous solution of the following is:
(A) $MgCl_2$
(B) $NaCl$
(C) $NH_2CONH_2$
(D) $K_3[Fe(CN)_6]$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (C), (B), (A), (D)
To determine the increasing order of osmotic pressure for these 0.1 M aqueous solutions, we use the formula for osmotic pressure ($\pi$):
$\pi = iCRT$
Since the molarity ($C = 0.1\text{ M}$), gas constant ($R$), and temperature ($T$) are the same for all solutions, the osmotic pressure depends entirely on the van't Hoff factor ($i$), which represents the number of particles the solute dissociates into.
Calculating the van't Hoff factor ($i$):
- (C) $NH_2CONH_2$ (Urea): This is a non-electrolyte. It does not dissociate in water, so $i = 1$.
- (B) $NaCl$ (Sodium Chloride): This salt dissociates into two ions: $Na^+$ and $Cl^-$. Thus, $i = 2$.
- (A) $MgCl_2$ (Magnesium Chloride): This salt dissociates into three ions: $Mg^{2+}$ and $2Cl^-$. Thus, $i = 3$.
- (D) $K_3[Fe(CN)_6]$ (Potassium Ferricyanide): This complex salt dissociates into four ions: $3K^+$ ions and $1[Fe(CN)_6]^{3-}$ complex ion. Thus, $i = 4$.