Is is possible to determine the percent composition of the target compound (in bold writing) in the mixture...

Question

...by heating with a Bunsen burner? In each case, explain your answer.

Ethyl alcohol (bold) in whiskey

CuSO4.4H2O/HgO (bold)

KClO3/CaCO3 (bold)

Hints:
1. Water of hydration (as in CuSO4.4H2O) can be driven out by strong heating.
2. When HgO is heated, it decomposes to Hg(l) and O2(g).
3. Carbonates (as in CaCO3) decompose upon heating yielding a metal oxide plus CO2(g).

Just for clarification, the target compounds in bold are ethyl alcohol, HgO, and CaCO3. For ethyl alcohol, maybe you could just use its empirical formula C2H6O.

Answer 1

Ethyl alcohol by heating in an open vessel – yes, but only if you are very careful and quick. While the alcohol evaporates the boiling point will be that of the alcohol (78 C). Once the alcohol is gone the boiling point will shift up to 100 C. As soon as the shift up in temperature starts, weight the boiling pot. You have a crude composition. However best to conduct this experiment with a fractionating column. I’ve tried it with even a simple distillation set-up and I was not pleased with the precision and accuracy.

Cinibar is great example for this question. Weight your starting mix. Heat it and form mercury metal. Pour off the mercury weigh what is left (or weigh your mercury). Assume that all the mercury recovered started as HgO.

The last two I do not like so much. While you can reduce these oxides with heat, you can’t be sure whether something else in the mixture is also loosing weight on heating. Further the first two examples created an isolated product, where in this one you are still left with a mixture after heating.