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Ways of Representing the Concentration of a Solution

The boiling p...

Question

The boiling point of water at 735 torr is 99.07°C. The mass of NaCl added in 100g water to make its boiling point 100°C is?(k=0.51 k kg/mol)

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Solution

Step 1:
Given that, $k_{b} = 0.51 K K g {m o l}^{- 1}$
$Δ T_{f} = 100 - 99.07 = {0.93}^{o} C$
Step 2:
Using the relation, $Δ T_{f} = K_{f} \times m$
$m = \frac{0.93}{0.51} = 1.824$
$\frac{n_{N a C l}}{W_{H_{2} O}} = 1.824$
Step 3:
$n_{N a C l} = 0.5 \times 1.824 \times 100 \times 10^{- 3} = 0.0911$
mass = $0.0911 \times 58.5 = 5.33 g$
Hence, the total amount of NaCl to be added is calculated as 5.33 g.

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