Silicon dioxide reacts with carbon upon heating to produce silicon carbide (sic) and carbon monoxide. sio2(s) + 3c(s) → sic(s) + 2co(g) a. what mass of carbon is required to react completely with 15.70 g of sio2? b. when 152 g of sio2 reacts with excess carbon, what mass of sic is produced? c. if 42.2 g of co were produced by this reaction, what mass of carbon must have reacted?

 Q1)
the balanced equation is ;
SiO₂(s) + 3C(s) → SiC(s) + 2CO(g)
stoichiometry of SiO₂ to C is 1:3
mass of SiO₂ reacted - 15.70 g
molar mass of SiO₂ - 60 g/mol
Number of SiO₂ moles that reacted - 15.70 g / 60 g/mol = 0.26 mol
Then the number of C moles that reacted - 0.26 mol x3 = 0.78 mol
Mass of C required - 0.78 mol x 12 g/mol = 9.36 g

Q2)
Stoichiometry of SiO₂ to SiC is 1:1
SiO₂ is the limiting reactant, therefore amount of product formed depends on amount of SiO₂ reacted.
Number of SiO₂ moles reacted - 152 g/ 60 g/mol = 2.53 mol 
Therefore number of SiC moles formed - 2.53 mol
molar mass of SiC - 40 g/mol
Mass of SiC formed - 2.53 mol x 40 g/mol = 101.2 g

Q3)
Stoichiometry of C to CO is 3:2
Molar mass of CO - 28 g/mol
Number of CO moles formed - 42.2 g / 28 g/mol = 1.5 mol 
2 mol of CO formed when - 3 mol of C reacts
When 1.5 mol of CO are formed - 3/2 x 1.5 mol = 2.25 mol of C reacted 
therefore 2.25 mol of C reacted
Mass of C reacted - 2.25 mol x 12 g/mol = 27 g

The total number of nucleons