PTHH: \(2Al+6HCl\rightarrow2AlCl_3+3H_2\uparrow\)
Ta có: \(\left\{{}\begin{matrix}n_{Al}=\dfrac{8,1}{27}=0,3\left(mol\right)\\n_{HCl}=\dfrac{21,9}{36,5}=0,6\left(mol\right)\end{matrix}\right.\)
Xét tỉ lệ: \(\dfrac{0,3}{2}< \dfrac{0,6}{6}\) \(\Rightarrow\) Al còn dư
\(\Rightarrow n_{H_2}=\dfrac{1}{2}n_{HCl}=0,3\left(mol\right)\) \(\Rightarrow V_{H_2}=0,3\cdot22,4=6,72\left(l\right)\)