100.0 g water 17.5 g compound -1.8℃

An aqueous solution containing 17.5 g of an unknown molecular (non electrolyte) compound in 100.0 g water has a freezing point of –1.8℃.

Calculate the molar mass of the compound.

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어는점내림

ΔTf = Kf × m

( 참고 https://ywpop.tistory.com/1920 )

m = ΔTf / Kf

= 1.8 / 1.86

= 0.9677 mol/kg

몰랄농도 = 용질 mol수 / 용매 kg수

( 참고 https://ywpop.tistory.com/2667 )

용질 mol수 = 몰랄농도 × 용매 kg수

= (0.9677 mol/kg) × (100.0/1000 kg)

= 0.09677 mol

몰질량 = 17.5 g / 0.09677 mol

= 180.84 g/mol

답: 180.84 g/mol

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