If the density of some lake water is 1.25 g ...

NCERT Class XII Chemistry
Chapter - Solutions
Questions with Solutions

Question : 26 of 53

Marks: +1, -0

If the density of some lake water is 1.25 g mL

^{-1}

and contains 92 g of Na

^{+}

ions per kg of water, calculate the molality of Na

^{+}

ions in the lake.

Solution:

Number of moles in 92 g of Na

^{+}

ions

= \frac{92 \, \mathrm{g}}{23 \, \mathrm{g} \, \mathrm{mol}^{-1}} = 4 \, \mathrm{mole}(

as atomic mass of

\mathrm{Na}=23)

As these are present in 1 kg of water, by definition molality = 4 m

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