In an analysis of copper sulfide, 12.7g of copper was found to be combined with 3.2 g of sulfur. Calculate the empirical formula.

So, the empirical formula means the smallest value, like the lowest common denominator in maths, but instead of fractions we are going to be using chemical formulae. I always find it easiest to set it out like a table, with the two elements involved in Copper sulphide at the top. Cu S12.7g 3.2gdivide each value by their molar mass, to get number of moles in each element. (12.7/62, 3.2/32) 0.2 0.1then divide each number of moles by the smallest number of moles calculated, to get the ratio. (0.2/0.1 =2, 0.1/0.1 = 1)2:1Therefore the compound will have two Cu atoms for every S atom, and the empirical formula will be Cu2.