Ncert Exercises & Solutions

2.26 If the density of some lake water is 1.25g mL–1 and contains 92 g of Na+ ions per kg of water, calculate the molality of Na+ ions in the lake.

Number of moles present in 92 g of Na⁺ ions

= \frac{92 g}{23 g {mol}^{- 1}}

= 4 mol

Therefore, molality of Na+ ions in the lake $= \frac{4 mol}{1 kg}$

= 4 m