The whole number mass ratio of copper to sulfur in copper (I) sulfide is 4:1. The whole number mass ratio of copper to sulfur in copper (II) sulfide is 2:1. A 60 g sample of copper sulfide contains 20 g of sulfur. Is the compound copper (I) sulfide or copper (II) sulfide

Your compound is Copper (II) sulfide

Explanation:

1 mol of Copper (I) sulfide (Cu₂S) contains 63.55gₓ2 = 127.1g of Cu and 32g of S. Thus, mass ratio is:

127.1g of Cu / 32g of S = 4

In Copper (II) sulfide, (CuS) mass of Cu is 63.55 g of and 32g of S. Thus, mass ratio is:

63.55g of Cu / 32g of S = 2

If your sample of 60g contains 20g of S, mass of Cu is 60g - 20g = 40g of Cu. Mass ratio in your sample is:

40g of Cu / 20g of S = 2.

As mass ratio is 2:1, your compound is Copper (II) sulfide