Question

The mole fraction of CO2 in a certain solution with H2O as the solvent is 3.6 × 10−4. What is the approximate molality of CO2 in this solution? A.0.00036 m.B.0.0065 m.C.0.020 m.D.2.0 × 10−5 m.E.6.5 m

Answer 1

Answer: C) 0.020 m

Explanation:

Molality of a solution is defined as the number of moles of solute dissolved per kg of the solvent.

$Molality=\frac{n\times 1000}{W_s}$

where,

n = moles of solute  

$W_s$ = weight of solvent in g  

Mole fraction of $CO_2$ is = $3.6\times 10^{-4}$ i.e.$3.6\times 10^{-4}$  moles of $CO_2$ is present in 1 mole of solution.

Moles of solute $(CO_2)$ = $3.6\times 10^{-4}$

moles of solvent (water) = 1 - $3.6\times 10^{-4}$ = 0.99

weight of solvent =$moles\times {\text {Molar mass}}=0.99\times 18=17.82g$

Molality =$\frac{3.6\times 10^{-4}\times 1000}{17.82g}=0.020$

Thus  approximate molality of $CO_2$ in this solution is 0.020 m