how do you calculate the mole fraction of HCl in an acqueous solution that contains 33.6% HCl by mass?

Answer 1

33.6% w/w HCl means 33.6 g HCl/100 g solution which means 33.6 g HCl/(33.6g HCl + 66.4 g H2O).
moles HCl = 33.6/molar mass HCl.
moles H2O = 66.4/molar mass H2O.
XHCl = moles HCl/total moles.
XH2O = moles H2O/total moles.