If 20 grams of calcium combines completely with 16 grams of sulfur to form a compound, what

is the percent composition of calcium in the compound?

55.56% of Ca

Explanation:

Percent composition is a therm in chemistry defined as the ratio by mass between an element and the compound formed from this element.

In the problem, 20g of Ca are combined with 16g of S to form a compound. The mass of the compound is:

20g + 16g = 36g

Thus, percent composition of calcium is:

20g Ca / 36g * 100 = 55.56% of Ca