Question

Mole fraction of methanol is 0.4 in methanol ethanol solution. What is the molality of the solution

Answer 1

Mole fraction of solute is related to molality by the following equation: $X_{a}=\frac{m\times MM(Solvent)} {1000+m\times MM(Solvent)}$

Where,  m is the molality

     MM(Solvent) is the molar mass of the solvent

         X is the mole fraction of the solute

   MM(ethanol)   is 46.07 g mol

    X is the mole fraction of the methanol is 0.4

Putting the values in the equation,

$0.4=\frac{m\times 46.07}{1000+m\times  46.07}$

 $0.4(1000+m\times  46.07)=(m\times 46.07)$

$400=(m\times 46.07)(1- 0.4)$

$m=\frac{400}{46.07\times  0.6)}$

m=14.4  

So, molality of solution is 14.4 m.