Suppose that after your second heating, you were impatient and did not wait until your porcelain evaporating?

Question

dish to cool. Instead, you weighed it while it was still hot. How would this specifically affect the calculated percentage of water in the compound

Answer 1

Remember that heat doesn't just vanish - it goes somewhere.

While your evaporating dish cools, it transfers heat to the water within it and the air around it. Some of that heat transferred to the water would have boiled some of it, so if you weigh too early, you have a higher percentage of water.