Hey there!
Consider 100 g of solution:
Mass of NaCl = 3.50% of mass of seawater
( 3.50 / 100 ) * 100 => 3.50 g
Number of moles as shown below:
Molar mass NaCl = 58.44 g/mol
n = Mass / molar mass
n = 3.50 / 58.44 => 0.059 moles of NaCl
Mass of sweater:
Mass of solution - Mass of NaCl
100 - 3.50 = 96.5 g
96.5 g in Kg :
96.5 / 1000 => 0.0965 Kg
Therefore ,calculate molality by using the following formula:
molality = number of moles of solute / mass of solution
molality = 0.059 / 0.0965
molality = 0.61 m
Hope That helps!
