Chemistry Lab Homework

Question

If a 0.192 g sample of copper metal reacts with elemental sulfur to form 0.240 g of the sulfide product, (a) find the percent by mass of copper and sulfur in the product and (b) find the empirical formula of the copper sulfide.

Answer 1

Cu(s) + S(s) ==> CxSy(s)

mass of Cu = 0.192 g

(a) % mass Cu = 0.192 g / 0.240 g (x100%) = 80.0%

(b) mass of CxSy = 0.240 g

mass of S = 0.240 g - 0.192 g = 0.048 g

moles Cu = 0.192 g x 1 mol/63.55 g = 0.0030 mols

moles S = 0.048 g x 1 mol/32 g = 0.0015 mols

Divide both by 0.0015 to get whole numbers and we end up with...

0.0030 / 0.0015 = 2 mols Cu

0.0015 / 0.0015 = 1 mol S

Empirical formula = Cu₂S