An unknown compound has the following chemical formula: Mg, C12
where x stands for a whole number.
Measurements also show that a certain sample of the unknown compound contains 4.3 mol of magnesium and 8.62 mol of chlorine.
Write the complete chemical formula for the unknown compound.

 MgCl2

Explanation:  The ratio of moles of Cl to Mg is 2 to 1 (8.62 mole Cl to 4.3 moles Mg).  The empiracle formula is therefore MgCl2

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o