Question

When 148. mg of a certain molecular compound X are dissolved in 75.g of cyclohexane (CH), the freezing point of the solution is measured to be 59 'C. Calculate the molar mass of X If you need any additional information on cyclohexane, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to l significant digit. XS ?

Answer 1

Answer: The molar mass of X is 61.3g/mol

Explanation:

Depression in freezing point is given by:

$\Delta T_f=K_f\times m$

$\Delta T_f=T_f^0-T_f=(6.55^0C-5.9^0C)=0.65^0C$ = Depression in freezing point

$K_f$ = freezing point constant = $20.2^0C/mol$

m= molality  = $\frac{\text{Mass of solute}}{\text{Molar mass of solute}\times \text{Mass of solvent in Kg}}$

where,  

Now put all the given values in this formula, we get

$0.65^0C=20.2°C/m\times frac{0.148g}}{M\times 0.075kg}$

$M=61.3g/mol$

Thus molar mass of X is 61.3g/mol