CHEMISTRY HELP: MOLAR MASS BOILING POINT?

2019-02-25 3:07 pm

The freezing point of benzene, C6H6, is 5.500 °C at 1 atmosphere. Kf(benzene) = 5.12 °C/m

In a laboratory experiment, students synthesized a new compound and found that when 13.77 grams of the compound were dissolved in 229.5 grams of benzene, the solution began to freeze at 4.633 °C. The compound was also found to be nonvolatile and a non-electrolyte.

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What is the molecular weight they determined for this compound?

回答 (1)

胡雪8°

2019-02-25 3:41 pm

Freezing point depression, ΔTf = (5.000 - 4.633) °C = 0.367 °C
Kf(benzene) = 5.12 °C/m
Molality, m = ? m

For non-electrolyte solute, ΔTf = Kf × m
Hence, m = ΔTf / Kf
Molality, m = (0.367 °C) / (5.12 °C/m) = 0.07168 m = 0.07168 mol/kg benzene

Moles of the compound dissolved = (0.07168 mol/kg benzene) × (229.5/1000 kg benzene) = 0.01645 mol
Molar weight for the compound = (13.77 g) / (0.01645 mol) = 837 g/mol

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