Question

You are asked to calculate the concentration of a NaCl (in water) solution in several ways and are given the following information: 20 g NaCl, 250 mL solution, 250 g H2O, Molecular weight of NaCl = 58.44 g/mole. Students must show ALL work for parts a and b.

(b) Calculate the mass/mass percent concentration (4 points).
(C) Calculate the molarity of the solution (6 points). (Points : 10)

Answer 1

B) The mass percentage of a solution is the ratio of the mass of solute to the mass of solvent expressed as a percentage. This becomes:
mass % = (NaCl mass) / (water mass) x 100
Mass % = 20 / 250 x 100
Mass % = 8%

C)
The molarity of a solution is the moles of solute present per liter of solution. The volume of the solution is:
250 mL = 0.25 L
Moles = mass / Mr
Moles = 20 / 58.44
Moles = 0.34

Molarity = moles / liter
Molarity = 0.34 / 0.25
Molarity = 1.36 M