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Hydrochloric acid and water form a maximum-boiling azeotrope with 20.2 % hydrogen chloride by mass…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Hydrochloric acid and water form a maximum-boiling azeotrope with hydrogen chloride by mass. Take the molar masses to be for hydrogen chloride and for water. Find the moles of hydrogen chloride in of this azeotrope and the mole fraction of hydrogen chloride in it.
Need a reminder? The key ideaShow
An azeotrope boils at one temperature and has the same composition in the liquid and in the vapour, so distillation cannot separate it. Positive deviation gives a minimum-boiling azeotrope, which comes off at the top of a column. Negative deviation gives a maximum-boiling azeotrope, which stays at the bottom.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Masses. Hydrogen chloride: . Water: .
Step 2. Moles. and .
Step 3. Mole fraction. .
Answer: of hydrogen chloride, and a mole fraction of .
Check. The acid is only about 11 % hydrogen chloride by moles, although it is 20 % by mass, because a hydrogen chloride molecule is twice as heavy as a water molecule.
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