This question is incomplete, the complete question is;
When 4.28 g of a certain molecular compound X are dissolved in 60.0 g of dibenzyl ether [(C₆H₅CH₂)₂0] , the freezing point of the solution is measured to be -3.2°C . Calculate the molar mass of X.
If you need any additional information on dibenzyl ether, use only what you find in the ALEKS Data resource. Also, be sure your answer has a unit symbol, and is rounded to significant digit.
Answer: molar mass of solute (X) is 88.03 g/mol
Explanation:
Given that;
mass of solute = 4.28 g
mass of solvent = 60.0 g = 0.060 kg (Dibenzyl ether)
depression constant kf = 6.17 °CKg/mol
Freezing Point of solvent T₀ = 1.80°C (Dibenzyl ether)
freezing point of solution Tsol = -3.20°C
Now we know that
Depression in freezing point ΔTf = depression constant kf × molaity m
and (ΔTf = T₀-Tsol)
so T₀ - Tsol = kf × m
we substitute
1.80 - (-3.20) = 6.17 × m
5 = 6.17 × m
m = 5 / 6.17
m = 0.8103 kg/mol
so molaity m = 0.8103 kg/mol
we know that
Molaity of solute m = (mass of solute / M.wt of solute) × ( 1 / mass of solvent in Kg)
solve for molar mass of solute
molar mass of solute = (mass of solute / molaity) × ( 1 / mass of solvent in Kg)
now we substitute
molar mass = (4.28g / 0.8103 kg/mol) × (1 / 0.060kg)
molar mass = ( 5.2839 × 16.66 ) g/mol
molar mass = 88.0297 g/mol ≈ 88.03 g/mol
Therefore molar mass of solute (X) is 88.03 g/mol
