The mass of the copper chloride is 9.902 g of which 6.356 is pure Copper, that makes 3.546 g Chloride. To determine the empirical formula you need to know that 1 mol of Cu is 63.54 g and 1 mol Cl is 35.45 g. 6.536/63.54= about .1 mol 3.546/35.45 is also about .1 mol so the empirical formula for this copper chloride would be CuCl
