Question

The water of lake contain 92 gm of na+ ion per kg and its density is 1.25 g/ml. Calculate the molality of na+ ion in the water

Answer 1

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 :

Density of lake water = 1.25 g mL-1

Amount of Na+ ion in one kg of water = 92 g Atomic mass of Na+ = 23 g mo1-1 Let V ml of lake water be taken.

Let take mass of solvent(water) = 1 Kg

Then mass of Na+ ions = 92 g

Number of moles of = 92/23 = 4 (molar mass of Na is 23g/mol)

Plug the values we get

Molality = 4 /1 = 4m

Solution molality of Na + ions = 4m