Molality of the solution is defined as the number of moles of a substance dissolved divided by the mass of the solvent:
Molality = number of moles / solvent mass
From the concentration of 39% (by mass) of HCl in water, we construct the following reasoning:
in 100 g solution we have 39 g hydrochloric acid (HCl)
number of moles = mass / molecular weight
number of moles of HCl = 39 / 36.5 = 1.07 moles
solvent (water) mass = solution mass - hydrochloric acid mass
solvent (water) mass = 100 - 39 = 61 g
Now we can determine the molality:
molality = 1.07 moles / 61 g = 0.018
Boiling-point is the point of a pure liquid matter starts to evaporate and change into gaseous phase. It is where the set of conditions such as the pressure and temperature enough to do so. Boiling-point elevation, on the other hand, is the phenomenon of which the boiling point of a pure liquid matter is elevated because of the dissolved substances. A great example would be the boiling point of a distilled water (pure water) which is lesser than the boiling point of a sea water because of the dissolved salts. A pure water boils at 100°C at atmospheric pressure while a salt water boils at higher temperature than 100°C at the same pressure. Thus, the answer is D.
