Đáp án:
55. A
57. D
Giải thích các bước giải:
\(\begin{array}{l}
55.\\
MgO + 2HCl \to MgC{l_2} + {H_2}O\\
MgC{O_3} + 2HCl \to MgC{l_2} + C{O_2} + {H_2}O\\
{n_{C{O_2}}} = 0,015mol\\
\to {n_{MgC{O_3}}} = {n_{C{O_2}}} = 0,015mol\\
\to {m_{MgC{O_3}}} = 1,26g\\
\to \% {m_{MgC{O_3}}} = \dfrac{{1,26}}{{2,06}} \times 100\% = 61,17\% \\
\to \% {m_{MgO}} = 100\% - 61,17\% = 38,83\%
\end{array}\)
\(\begin{array}{l}
57.\\
2NaOH + {H_2}S{O_4} \to N{a_2}S{O_4} + 2{H_2}O\\
{n_{NaOH}} = 0,5mol\\
\to {n_{{H_2}S{O_4}}} = \dfrac{1}{2}{n_{NaOH}} = 0,25mol\\
\to {V_{{H_2}S{O_4}}} = \dfrac{{0,25}}{2} = 0,125l
\end{array}\)
