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Korolek
2 months ago
5

A solution containing 0.050 g of an unknown nonelectrolyte in 2.50 g of cyclohexane (Kf = 20.4 oC/m & F.P. 6.6 oC) was found

to freeze at 5.0 oC. What is the molar mass of the unknown substance?
Chemistry
1 answer:
Tems11 [2.7K]2 months ago
7 0

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

<pthus mole="" weighs="" g="" moles="">

</pthus>
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