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Concentration Terms - An Introduction (w/w etc)

150 g of an u...

Question

$150 g$ of an unknown molecular material was dissolved in $450 g$ of water. The resulting solution was found to freeze at $- {0.64}^{o} C$ . What is the molar mass of this material? ( $K f$ for water $= 1.86 g m o l^{- 1}$ )

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Solution

Using the relation, $Δ T_{f} = m K_{f}$

Hence, $0.64 = 1.86 \times m$

$\Rightarrow m = 0.344$
$\Rightarrow \frac{\frac{150}{M}}{0.450} = 0.344$

$\Rightarrow M = 969 g / m o l$

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Concentration Terms - An Introduction (w/w etc)

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