Calculate the mole fraction of HCl in a 10.0% (by mass) aqueous solution.

Question

Calculate the mole fraction of HCl in a 10.0% (by mass) aqueous solution.

Answer is 0.0520, why?

Answer 1

10% by mass means that you have 10 g HCl per 100 g of solution. Since the problem states that it is an aqueous solution, we know the solvent is water. So, we have 10 g HCl + 90 g H2O

moles HCl = 10 g x 1 mole HCl/36.45 g = 0.274 moles HCl

moles H2O = 90 g H2O x 1 mole/18 g = 5 moles H2O

Total moles in the solution = 0.274 + 5 = 5.274 moles

mole fraction HCl = 0.274/5.274 = 0.05195 = 0.052