Question

Determine the amount of $CaC{l}_2(i=2.47)$ dissolved in $2.5$ litre of water such that its osmotic pressure is $0.75$ atm at ${27}^{\circ }C$.

Answer 1

According to Van't Hoff's equation, the osmotic pressure

$\Pi =iCRT=\frac{i{n}_{B}RT}{V}$.

Here, $i$ is the Van't Hoff's factor, $C$ is the molar concentration, $R$ is the ideal gas constant, $T$ is temperature, $nB$ is the number of moles of calcium chloride and $V$ is the volume of the solution.

Now we have given below values:

π = 0.75 atm

V = 2.5L

i = 2.47

T = (27+273) K = 300K

and R = 0.0821L atm k${}^{-1}$ mol${}^{-1}$

$0.75=\frac{2.47\times n_B\times 0.0821\times 300}{2.5}$

$n_B=0.0308$ mol

The molar mass of calcium chloride is $111$ g/mol.

Amount of calcium chloride dissolved $=0.0308\times 111=3.42$ g.