Question

What is the molarity of an aqueous solution that contains 9.45% (w/w) NaCl? (Assume that the density of this solution is 1.00 g/mL)

Answer 1

Let volume of solution be 1 L

volume , V = 1 L

= 1*10^3 mL

density, d = 1.0 g/mL

use:

mass = density * volume

= 1 g/mL *1*10^3 mL

= 1*10^3 g

This is mass of solution

mass of NaCl = 9.45 % of mass of solution

= 9.45*1000.0/100

= 94.5 g

Molar mass of NaCl,

MM = 1*MM(Na) + 1*MM(Cl)

= 1*22.99 + 1*35.45

= 58.44 g/mol

mass(NaCl)= 94.5 g

use:

number of mol of NaCl,

n = mass of NaCl/molar mass of NaCl

=(94.5 g)/(58.44 g/mol)

= 1.617 mol

volume , V = 1 L

use:

Molarity,

M = number of mol / volume in L

= 1.617/1

= 1.617 M

Answer: 1.62 M