Question

1. A solution contains 20.5 g of sodium chloride dissolved in sufficient water to give a total mass of 166.2 g. What is the molality of the solution?

Answer 1

Mass of Sodium chloride ( NaCl ) = 20.5 g

Molar mass of Sodium Chloride ( NaCl )

= 58.5 g / mol.

Moles of Sodium Chloride = 20.5 / 58.5 mol.

= 0.350 mol.

Total Mass of water = 166.2 g .

Density of water = 1 g / ml .

So, Volume of water = 166 .2 ml .

For Dilute Solution

Volume of water = Volume of Solution

= 166.2 ml. = 0.1662 litre .

Molarity =

moles of NaCl / Volume of Solution in litre .

= 0.350 mol . / 0.1662 litre.

= 2.1058965102 M

= 2.11 M

= 2.11 mol/ litre .