Question

A student is tasked with determining the concentration of an unknown aqueous sodium chloride (NaCL) solution. A 10.0 mL sample of the solution weighs 21.6 g. The sample is heated over a flame. As it is heated, the water solvent evaporates, leaving a dried NaCl solute residue. After drying, the dish is reweighed and the residue is found to have a mass of 0.8 grams.
Concentration calculations:
Calculate the mass/mass percent, mass/volume percent, and molarity of the NaCl solution according to the following:
a. Mass/mass % = mass (g) of dried NaCl residue / mass (g) of NaCl solution
b. Mass/volume % = mass (g) of dried NaCl residue / volume (mL) of NaCl sln.

Answer 1

mass/mass percent = mass of solute / mass of solution*100

              = 0.8/21.6*100

              = 3.7%

mass/volume percent = mass of solute / volume of solution*100

                      = 0.8/10*100

                      = 8%

molarity of the NaCl solution = (m/v%)*10/Mwt

Mwt = molarmass of NaCl = 58.5 g/mol

m/v% = 8%

        = 8*10/58.5

   Molarity(M) = 1.37 M