Calculate the number of moles of nonvolatile solute dissolved in 0.5 kg solvent if molal elevation constant for solvent is 2 kg K mol − 1 [ Δ T b = 0.8 K ]

Question

Calculate the number of moles of nonvolatile solute dissolved in 0.5 kg solvent if molal elevation constant for solvent is 2 kg K mol − 1 [ Δ T b ​ = 0.8 K ]

TestHub · Accepted Answer

The elevation in boiling point is given by:

$Δ T_{b} = K_{b} \times m$

where $m$ is the molality of the solution.

$0.8 = 2 \times m$

$m = \frac{0.8}{2} = 0.4 mol kg^{- 1}$

Molality is the number of moles of solute $n$ per kg of solvent $W$ :

$m = \frac{n}{W}$

$0.4 = \frac{n}{0.5}$

$n = 0.4 \times 0.5 = 0.2 mol$

Answer: 0.2

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