# 15.0 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution freezes at – 0.34°C.

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15.0 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution freezes at – 0.34°C. What is the molar mass of the material? Kf for water = 1.86 K kg mol-1.

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W(solute) = 1 5.0 g

W(solvent) = 450 g

∆Tf = T°f – Tf = 0 - (-0.34) = 0.34 °C

∆Tf = km

0.34 = 1.86 x $\frac{15}{M}$ x $\frac{1000}{450}$

M = $\frac{1.86\times 15\times1000}{0.34\times450}$

= 182.35 g mol-1