PTHH: \(Mg+2HCl\rightarrow MgCl_2+H_2\)
Ta có: \(n_{Mg}=\dfrac{4,8}{24}=0,2\left(mol\right)\)
\(\Rightarrow\left\{{}\begin{matrix}n_{HCl}=0,4\left(mol\right)\\n_{MgCl_2}=0,2\left(mol\right)=n_{H_2}\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}C\%_{HCl}=\dfrac{0,4\cdot36,5}{100}\cdot100\%=14,6\%\\m_{MgCl_2}=0,2\cdot95=19\left(g\right)\\m_{H_2}=0,2\cdot2=0,4\left(g\right)\end{matrix}\right.\)
\(\Rightarrow C\%_{MgCl_2}=\dfrac{19}{4,8+100-0,4}\cdot100\%\approx18,2\%\)