Em tham khảo nha:

\(\begin{array}{l}
5)\\
Fe + 2HCl \to FeC{l_2} + {H_2}\\
Mg + 2HCl \to MgC{l_2} + {H_2}\\
n{H_2} = \dfrac{1}{2} = 0,5\,mol\\
hh:Fe(a\,mol),Mg(b\,mol)\\
56a + 24b = 20\\
a + b = 0,5\\
 \Rightarrow a = b = 0,25\,mol\\
\% mFe = \dfrac{{0,25 \times 56}}{{20}} \times 100\%  = 70\% \\
\% mMg = 100 - 70 = 30\% \\
b)\\
m = mFeC{l_2} + mMgC{l_2} = 0,25 \times 127 + 0,25 \times 95 = 55,5g\\
6)\\
Zn + C{l_2} \to ZnC{l_2}\\
nZnC{l_2} = \dfrac{{27,2}}{{136}} = 0,2\,mol\\
H = 90\%  \Rightarrow nZn = nC{l_2} = \dfrac{{0,2}}{{90\% }} = \dfrac{2}{9}(mol)\\
mZn = \dfrac{2}{9} \times 65 = 14,44g\\
VC{l_2} = \dfrac{2}{9} \times 22,4 = 4,98l\\
7)\\
2{H_2} + {O_2} \to 2{H_2}O\\
2KOH + C{l_2} \to KCl + KClO + {H_2}O
\end{array}\)