Question

A student heated a 0.8702 g sample of copper(II) sulfate pentahydrate several times until all water was removed. The mass of the residue in the crucible was found to weigh 0.5557 grams.

Another student completed the same experiment and found a mass of 0.4098 grams of residue. What was the mass of the copper(II) sulfate pentahydrate used in this experiment?

Answer 1

0.6402 but not entirely sure.

Answer 2

the masses of sample used in each expt were different, but the percentage of water in each must be the same (law of constant proportions). Find the % of water lost by the first experiment, and that % must also be lost from the original mass in the second expt.

Answer 3

How did you get 0.6402?