An unknown, clear liquid is given to you in a beaker. you transfer some of the liquid from the beaker to a clean, empty test tube, and begin to heat it. soon, you observe a vapour leaving the top of the test tube. with further analysis you discover that the vapour is water vapour. eventually, all that's left are a few crystals stuck to the sides of the test tube. was the original liquid an element, a compound, or a mixture? explain