First, we need to find the amount in moles of each substance. WE have the mass for each so we use the formula:
#n = m/M#
Where #n# is the amount of the substance in moles, #m# is the mass of the substance, and #M# is the molar mass or molecular mass of the substance, which we can find by looking at the atomic mass on a periodic table so:
#n("Cu") = (8.882g)/(63.546gmol^-1) = 0.139772763mol#
and:
#n(O) = (10g-8.882g)/(15.9994gmol^-1) = 0.06987762041mol#
Now we find the ratio of the copper and oxygen by dividing both values by the lowest value:
#Cu:O = (0.139772763mol)/(0.06987762041mol):(0.06987762041mol)/(0.06987762041mol)#
#= 1.999535219 : 1#
The value of 1.999535219 can be rounded to 4 significant figures to get a ratio of #2:1#, as the figures in the question are given to 4 s.f.
From this ratio we can get the empirical formula of #Cu_2O#
