1) calculate the number of moles for copper and sulfur by dividing its mass with its molar mass..
number of moles of copper=0.0125
number of moles of sulfur=0.025
next we do a ratio of the two compounds:
Cu : S = 0.0125 : 0.025 = 1 : 2...
thus we get the empirical formula as
2)for question 2 i will do the mass composition for u...
copper percent= (mass of copper / mass of copper sulfide) X 100%
=( 0.7943/1.5960) X 100%
=49.8 %
do the same for sulfur, and u get= 50.2 %