Question

Assuming that seawater is a 3.50 mass % aqueous solution of NaCl, what is the molality of seawater?

Answer 1

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!