Question

For an experiment we measured out 0.254g of copper and 0.495g of sulfur. The copper and sulfur were mixed in a crucible with a clean spatula and then heated until no more sulfur fumes evolved. The mass of the product was 0.297g. What is the mole ratio of copper and sulfur in copper sulfide. It is stated in litertature that copper completely combines with sulfur in a mole ratio of roughly 1.8:1 or 9:5, compare your result.

Answer 1

We have 0.254 g Cu

0.495g S both are heated together to form a Copper -sulphur compound

total mass of product = 0.297g

S is more volatile than Cu and hence it will vaporize

total S present in sample = 0.297 - 0.254 = 0.043g

molar mass of Cu = 63.546 g/mol

0.254g Cu = 0.254g / 63.546 g/mol = 0.003997 mol

0.043g S = 0.043g / 32g/mol = 0.00134375 mol

divide by smallest no. to get integer of components

0.003997 / 0.00134375 = 2.97

Cu:S = 2.97:1 ~ 3 :1 is the mole ratio