Question

An NaCl solution is labeled as having a concentration of 33.5% by mass. If the NaCl

solution has a density of 1.0492 g/mL, what is the molarity of the solution?

Answer: 6.01 M

Answer 1

Concentration of NaCl = 33.5 % by mass = 33.5 % m/m

= (mass of NaCl/total mass of solution) ×100

33.5% m/m implies 33.5 gms of NaCl is present in 100 gms of solution

Density of NaCl solution = 1.0492 g/ml

1.0492 gms of NaCl solution is present in 1 ml of solution

100 gms of NaCl solution is present ----> ?? =

== 100 gms ×1ml/1.0492 gms = 95.311 ml = 0.095311 lts

Molar mass of NaCl = 58.44 g/mol

No. Of moles of NaCl = wt of NaCl/molar mass = 33.5 gms/58.44 g/mol = 0.573 moles

Molarity of NaCl solution = no. Of moles of NaCl/vol of NaCl solution in lts == 0.573 moles/0.095311 lts = 6.01 moles/lt or 6.01 M