a, PT: \(2Al+6HCl\rightarrow2AlCl_3+3H_2\)
Ta có: \(n_{Al}=\dfrac{2,7}{27}=0,1\left(mol\right)\)
Xét tỉ lệ: \(\dfrac{0,1}{2}>\dfrac{0,25}{6}\), ta được Al dư.
Theo PT: \(n_{H_2}=\dfrac{1}{2}n_{HCl}=0,125\left(mol\right)\Rightarrow V_{H_2}=0,125.22,4=2,8\left(l\right)\)
b, Theo PT: \(n_{Al\left(pư\right)}=\dfrac{1}{3}n_{HCl}=\dfrac{1}{12}\left(mol\right)\Rightarrow n_{Al\left(dư\right)}=0,1-\dfrac{1}{12}=\dfrac{1}{60}\left(mol\right)\)
\(\Rightarrow m_{Al}=\dfrac{1}{60}.27=0,45\left(g\right)\)