Question

The commercial concentrated hydrochloric acid is rated at 38 w/w%. The density of the solution is d = 1.18g.mL. Calculate the molarity of HCl (cHCl), molality of HCl (cR,HCl), and the mole fraction of HCl (xHCl).

Answer 1

Assume 100 grams of the solution, which means there are 37.0 g HCl in 100 grams solution.

Since,

Molarity = moles / L

Density = Mass / Volume

Convert the mass of HCl to moles and the mass of the solution to volume to determine molarity.

Moles of HCl = 37.0g / 36.5 g/mol = 1.014 moles

Volume of solution = 100 g / 1.18 g/mL = 84.75 mL = 0.08475 L

Molarity of HCl = 1.014 moles / 0.08475 L = 11.96 M

Molality = moles / Kg

             = 1.014 moles / 0.1 Kg = 10.14 m

Mass of water = 100 g – 37 g = 63 g

Molar mass of water = 18g/mol

Moles of water = (63 / 18) mol = 3.5 mole

Mole fraction of HCl = mole of HCl / Total mole

                                 = 1.014 mole / (1.014 mole + 3.5 mole)

                                 = 1.014 mole / 4.514 mole

                                 = 0.225