a)PTHH: $2Al+6HCl\rightarrow 2AlCl_{3}+3H_{2}$
b)Ta có: $n_{Al}=\frac{m}{M}=\frac{8,1}{27}=0,3(mol)$
$n_{HCl}=\frac{m}{M}=\frac{21,9}{36,5}=0,6(mol)$
TL:$\frac{0,3}{2}> \frac{0,6}{6}$
$\Rightarrow $ Al dư, HCl phản ứng hết
Theo pt: $n_{AlCl_{3}}=\frac{1}{3}.n_{HCl}=\frac{1}{3}.0,6=0,2(mol)$...