Question

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.

Answer 1

Density = 1.25gmL-1.

Let us find molality.Molality = Number of moles of solute / Mass of solvent in Kg.

Number of moles of solute  = Mass of glucose / Molar mass of glucose.

Molar mass of glucose Na + = 23  g /mol.

Number of moles 92 gm Na +==  92/23  = 4 moles.Molality  =4 M

Answer 2

Hey !!

Number of moles of Na⁺ ion = 92 g / 23 g mol⁻¹    

            = 4 mol

Molality of Na⁺ ions = Number of moles of Na⁺ ions / Mass of water in kg

           = 4 mol / 1 kg

           = 4 mol kg⁻¹

           = 4 m

Hope it helps you !!