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When 908.0 mg of a certain molecular compound X are dissolved in 40.0 g of dibenzyl ether ((C₆H₅CH₂)₂O), the freezing point of the solution is measured to be -3.2 °C.
Calculate the molar mass of X.

Respuesta :

Answer: Molar mass of X is 106 g/mol

Explanation:

Depression in freezing point is given by:

[tex]\Delta T_f=i\times K_f\times m[/tex]

[tex]\Delta T_f=T_f^0-T_f=(3.6-3.2)^0C=0.4^0C[/tex] = Depression in freezing point

i= vant hoff factor = 1 (for non electrolyte)

[tex]K_f[/tex] = freezing point constant = [tex]1.86^0C/m[/tex]

m= molality

[tex]\Delta T_f=i\times K_f\times \frac{\text{mass of solute}}{\text{molar mass of solute}\times \text{weight of solvent in kg}}[/tex]

mass of solute = 908.0 mg = 0.9080 g     (1g=1000mg)

Weight of solvent (dibenzyl ether)= 40.0 g = 0.04kg

Molar mass of solute (KCl) = 74.5 g/mol

Mass of solute = ?

[tex]0.4^0C=1\times 1.86\times \frac{0.9080g}{Mg/mol\times 0.0400kg}[/tex]

[tex]M=106g/mol[/tex]

Thus the molar mass of X is 106 g/mol

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