Question

A greenish blue salt known to be composed of copper and chloride ions is dissolved in DI water. Aluminum metal is used to reduce the copper ions to metallic, copper, which is then collected, dried and weighed. If the original sample has mass 1.362g and the collected copper has mass .635g, what is the empirical formula of the compound?

Answer 1

Given that salt is composed of copper and chloride ions and mass of sample 1.362g and the collected copper has mass 0.635g,

So mass of Cl- = 1.362 g – 0.635 g

= 0.727 g

Now calculate the moles of Cu and Cl as follows:

Cu = 0.635 g/ molar mass ; 63.546 g/mol

= 0.009 moles

Cl:

0.727 g/35.45 g/ mole

= 0.021 moles

Now molar ratio of Cu and Cl as follows:

Cu: 0.009 moles / 0.009 moles

=1

Cl= 0.021 moles /0.009 moles

= 2.33

Thus the empirical formula is CuCl2