Answer:
The molar mass for the unidentified substance is 255g/mole
Explanation:
The freezing point depression can be calculated using
ΔT = i · Kf · m
Where
m = molality of the solute
i = van't Hoff's factor = 1 for non-electrolytes
Kf = 20.4 °C/m = cryoscopic constant
ΔT = Freezing point depression
Thus, ΔT = 6.6 - 5 = 1.6 °C
1.6 °C = 20.4 °C/m × 1 × m
Hence, m = 1.6/20.4 = 0.0784 m
The number of moles in 2.50 g of cyclohexane = 0.0784 m or 0.0784 moles of the substance in 1000 grams of cyclohexane, meaning
2.5 × 0.0784/1000 results in moles for 2.5 grams of cyclohexane that equal
1.96 × 10⁻⁵ moles within 2.5 grams of cyclohexane
1.96 × 10⁻⁵ moles of this substance weighs 0.050 grams
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