Question 5
Why is steam used to supply the heat when extracting an essential oil?
The right answer is the one marked above.
Because heating them to their own boiling point would destroy them. At temperatures near their boiling point these compounds can decompose, or be converted into other compounds entirely.
Steam works because these oils do not mix with water, which makes the boiling point of the mixture fall below that of water. A compound that mixed well with water would behave the opposite way.