Question

1-Common commercial acids and bases are aqueous solutions with the following properties: HCl, density 1.19 g/cm³ and 34% solute by mass. Calculate the molality.

2-Common commercial acids and bases are aqueous solutions with the following properties: HCl, density 1.19 g/cm³ and 35% solute by mass. Calculate the mole fraction.

Answer 1

1)

Let mass of solution be 1 Kg = 1000 g

mass of HCl = 34.0 % of mass of solution

= 34.0*1000.0/100

= 340.0 g

mass of solvent = mass of solution - mass of solute

mass of solvent = 1000 g - 340.0 g

mass of solvent = 660.0 g

mass of solvent = 0.66 Kg

Molar mass of HCl = 1*MM(H) + 1*MM(Cl)

= 1*1.008 + 1*35.45

= 36.458 g/mol

mass of HCl = 340.0 g

we have below equation to be used:

number of mol of HCl,

n = mass of HCl/molar mass of HCl

=(340.0 g)/(36.458 g/mol)

= 9.326 mol

mass of solvent = 0.66 Kg

we have below equation to be used:

Molality,

m = number of mol / mass of solvent in Kg

=(9.326 mol)/(0.66 Kg)

= 14.13 molal

Answer: 14.1 molal

2)

As in 1:

moles of HCl = 9.326 mol

moles of H2O = mass of H2O / molar mass of H2O

= 1000 g / 18 g/mol

= 55.56 mol

mole fraction= moles of HCl / total moles

= 9.326 / (9.326 + 55.56)

= 0.144

Answer: 0.144