John put a sample of a white solid substance, labeled A, into a test tube and th

Question

John put a sample of a white solid substance, labeled A, into a test tube and then left the
laboratory room. While John was out of the room, Mary heated the test tube in a Bunsen
burner and then let the test tube cool back to room temperature. At this point, John
returned to the lab and found a white solid in the test tube he had left. Is possible for
John to tell if anything was done to substance A while he was out of the room? What
could John do to determine whether substance A underwent a chemical reaction?

Explanation / Answer

He may see that the testube has blackened at the bottom and thus knowing that something has happened

JOHN might see some powder on the side of the tube OR that the testube has been darkened at the bottom(change in colour).

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