2CH4 +3O2 ---> 2HCooH + 2 Н2о
V(CH4)= J x V= 420 x0.96= 403.2 л
n(CH4)= 403.2/22.4=18 моль
n(CH4)=n(HCOOH)
m(HCOOH) = n x M=46 х 18=828 г
m(HCOOH)= 828 x0.7= 579.6 г