42.2 g of KCl is dissolved in 368g of water. Calculate the molality of a solution.

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42.2 g of KCl is dissolved in 368g of water. Calculate the molality of a solution.

Strategy:

To calculate the molality of a solution, we need to know the number of moles of solute and the mass of the solvent in kilograms.

Solution:

The definition of molality (m) is

First, we find the number of moles of KCl in 42.2 g of KCl, using its molar mass as the conversion factor.

\text{moles of KCl} = \text{42.2 g KCl} \times \frac{\text{1 mol KCl}}{\text{74.55 g KCl}}

\text{moles of KCl} = \text{0.56606 mol KCl}

The mass of water is 368 g, or 0.368 kg. Therefore,

m = \frac{\text{0.56606 mol KCl}}{\text{0.368 kg H₂O}}

\blue{m = 1.54 \: m}

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