Question

A solution of sodium sulphate contains 92 g of na+

Answer 1

If the density of some lake water is 1.25 g mL-1and 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

Answer 2

$\frac{92}{23} = 4moles \: of \: na {}^{ + } \\ molality = 4 \div 1 = 4m$