Astudent allows the evaporating dish and the anhydrous salt for a long time on the lab bench. what will happen to the mass of the content of the evaporating dish as it cools and how could this be prevented? g

Anhydrous salts absorb moisture from their surroundings when it gets cooled, hence the mass of the content would increase. It can be prevented if we allow the evaporating dish to cool in a dessicator. A dessicator is a glass or plastic container in which chemicals can be stored and allowed to cool. This container can be sealed. Dessicator would provide an environment free of moisture instead of keeping in atmospheric air having moisture content.

some think that theories become laws, but theories and laws have separate and distinct roles in the scientific method. a law is a description of an observed phenomenon in the natural world that hold true every time it is tested. it doesn't explain why something is true; it just states that it is true.