PTHH: Fe+H2SO4--->FeSO4+H2 (1)
Fe2O3+3H2SO4--->Fe2(SO4)3+3H2O (2)
nH2=\(\dfrac{6,72}{22,4}=0,3\) mol
Theo pt(1): nFe=nH2=0,3 mol
=> mFe=0,3.56= 16,8 (g)
mFe2O3=48,8-16,8= 32 (g)
=> %Fe=\(\dfrac{16,8}{48,8}.100\%\approx34,43\) %
%Fe2O3=100%-34,43%= 65,57%