Bài $1:$$2FeS_2\overset{HNO_3}{\rightarrow}Fe_2(SO_4)_3+H_2SO_4$
$Cu_2S\overset{HNO_3}{\rightarrow}CuSO_4+Cu(NO_3)_2$
$\Rightarrow 2FeS_2+Cu_2S\overset{HNO_3}{\rightarrow}Fe_2(SO_4)_3+2CuSO_4$
$x:y=2:1$
Bài $2$
$FeO_\overline{n}+2\overline{n}HCl\rightarrow FeCl_{2\overline{n}}+\overline{n}H_2O $
$x 2x\overline{n} $
$\Rightarrow 2x\overline{n}=0,26\Rightarrow x\overline{n}=0,13\Rightarrow \frac{7,68}{56+16\overline{n}}.\overline{n}=0,13\Rightarrow \overline{n} =1,3\Rightarrow x=0,1 $
$\Rightarrow m_{Fe_2O_3}=\frac{0,1}{2}.160=8 gam$