Question

a mixture of carbon and sulfur has a mass of 9.0 g. complete combustion with excess o2 gives 22.5 g of a mixture of co2 and so2. find the mass of sulfur in the original mixture.

Answer 1

S + O2 → SO2 
z / (32.0655 g S/mol) x (1 mol SO2 / 1 mol S) x (64.0638 g SO2/mol) = (1.9979 z) g SO2 

C + O2 → CO2 
(9.0-z) / (12.01078 g C/mol) x (1 mol CO2 / 1 mol C) x (44.00964 g CO2/mol) = (32.9776 - 3.66418 z) g CO2 

Add the two masses of SO2 and CO2 and set them equal to the amount given in the problem: 
(1.9979 z) + (32.9776 - 3.66418 z) = 27.9 
Solve for z algebraically: 
z = 3.0 g S