a) \(n_{O_2}=\dfrac{2,8}{22,4}=0,125\left(mol\right)\)
PTHH: 2H2 + O2 --to--> 2H2O
____0,25<-0,125
=> mH2 = 0,25.2 = 0,5 (g)
=> mN2 = 4,7 - 0,5 = 4,2 (g)
b)
\(n_{N_2}=\dfrac{4,2}{28}=0,15\left(mol\right)\)
=> \(\overline{M}=\dfrac{4,7}{0,15+0,25}=11,75\left(g/mol\right)\)
=> \(d_{hh/He}=\dfrac{11,75}{4}=2,9375\)