Giải thích các bước giải:

Câu 3:

\(\begin{array}{l}
1.C{\% _{{\rm{CuS}}{O_4}}} = \dfrac{{10}}{{200}} \times 100\%  = 5\% \\
2.{m_{Na}} = \dfrac{{200 \times 0,9\% }}{{100\% }} = 1,8g
\end{array}\)

Câu 4:

\(\begin{array}{l}
1.\\
Mg + 2HCl \to MgC{l_2} + {H_2}\\
{n_{Mg}} = 0,15mol\\
 \to {n_{{H_2}}} = {n_{Mg}} = 0,15mol\\
 \to {V_{{H_2}}} = 0,15 \times 22,4 = 3,36l\\
2.\\
{n_{HCl}} = 2{n_{Mg}} = 0,3mol\\
 \to {V_{HCl}} = \dfrac{{0,3}}{1} = 0,3l = 300ml\\
3.\\
{m_{{\rm{dd}}HCl}} = 300 \times 1,2 = 360g
\end{array}\)

Câu 5:

\(\begin{array}{l}
2Na + {O_2} \to N{a_2}O\\
{n_{Na}} = 0,3mol\\
{n_{{O_2}}} = \dfrac{1}{2}{n_{Na}} = 0,15mol\\
 \to {V_{{O_2}}} = 0,15 \times 22,4 = 3,36l\\
N{a_2}O + {H_2}O \to 2NaOH\\
{n_{NaOH}} = {n_{N{a_2}O}} = \dfrac{1}{2}{n_{Na}} = 0,15mol\\
 \to {m_{NaOH}} = 0,15 \times 40 = 6g\\
 \to C{\% _{NaOH}} = \dfrac{6}{{180}} \times 100\%  = 3,33\% 
\end{array}\)