# 2.26   If the density of some lake water is $\inline 1.25g\; mL^{-1}$ and contains $\inline 92\; g$ of $\inline Na^{+}\; ions$ per kg of water, calculate the molality of $\inline Na^{+}\; ions$ in the lake.

We know that, Molality :

$Molality = \frac{Moles\ of\ solute}{Mass\ of\ solvent\ in\ Kg}$

So, for moles of solute we have :

$Moles\ of\ Na^+ = \frac{92}{23} = 4$

Thus,  molality :

$= \frac{4}{1} = 4$

Molality of Na+ ions is 4m.

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