How many grams are in 7.2*10^24 atoms of Ca?

The answer to your question is 478.2 g of Ca

Explanation:

Data

mass of Ca = ?

atoms of Ca = 7.2 x 10²⁴

Process

To solve this problem you must remember that 1 mol of any substance equals Avogadro's number.

1.- Look for the atomic number of Calcium

Atomic number = 40 g

2.- Use proportions to calculate the atoms of Ca

                    40 g of Ca 6.023 x10²³ atoms

                      x               7.2 x 10²⁴ atoms

                            x = (40 x 7.2 x 10²⁴) / 6.023 x 10²³

                            x =2.88 x 10²⁶ / 6.023 x 10²³

                            x = 478.2 g

alchemy hadn't scientific methods of study, appeal to mysticism and fantasy, the knowledge of chemistry and physics were modest at that time.

alchemy was - but as new rules were discovered it either changed into chemistry or it became "unscientific".