At the end we stopped the distillation with some material left in the vial. Why is it considered unsafe to distill until dryness?

See the answer below

Explanation:

Distillation is a process of separating the contents of a liquid mixture by making use of the difference in the boiling temperatures of the components of the mixture. As the boiling point of each component is reached, it evaporates off and the vapor is condensed and collected to give a pure product.

It is never advisable to distillate to dryness because allowing the content of the distilling flask to dry up can cause heat to damage the flask or in some extreme cases, cause unintended chemical reactions that might alter the outcome of the experiment or cause laboratory accident.

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acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.