PTHH: \(Fe+S\xrightarrow[]{t^o}FeS\)
Ta có: \(\left\{{}\begin{matrix}n_{Fe}=\dfrac{2,8}{56}=0,05\left(mol\right)\\n_S=\dfrac{3,2}{32}=0,1\left(mol\right)\end{matrix}\right.\) \(\Rightarrow\) Lưu huỳnh còn dư
\(\Rightarrow n_{FeS}=0,05\left(mol\right)=n_{S\left(dư\right)}\) \(\Rightarrow\left\{{}\begin{matrix}m_{FeS}=0,05\cdot88=4,4\left(g\right)\\m_{S\left(dư\right)}=0,05\cdot32=1,6\left(g\right)\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}\%m_{FeS}=\dfrac{4,4}{4,4+1,6}\cdot100\%\approx73,33\%\\\%m_{S\left(dư\right)}=26,67\%\end{matrix}\right.\)