Question

During the combustion of 5.00 g of Butane in the presence of oxygen, 4.01 g of carbon dioxide and 3.55 g of water is given off. How much oxygen was needed to totally combust the butane?
Iron combines with 4.00 g of Copper (11) nitrate to form 6.01 g of Iron (I) nitrate and 0.400 g copper metal. How much iron did it take to convert the Cu(NO3)2?

Answer 1

How much oxygen was needed to totally combust the butane? 

C4H10 + 13/2O2 = 4CO2 + 5H2O
5.00 g C4H10 ( 1 mol / 58.12 g ) (13/2 / 1) ( 32 g / mol ) = 17.89 g O2

How much iron did it take to convert the Cu(NO3)2?

Fe + Cu(NO3)2 = Cu + Fe(NO3)2 
4.00 g of Copper (11) nitrate ( 1 / 187.56 ) (1 mol / 1 mol ) (55.85 g / mol) = 1.19 g Fe