Đáp án:

 Em xem lại câu 3 nha

\(\begin{array}{l}
a)\\
{C_M}C{H_3}COOH = 0,8M\\
{V_{{H_2}}} = 2,24l\\
b)\\
{V_{{\rm{dd}}NaOH}} = 0,4l
\end{array}\)

Giải thích các bước giải:

\(\begin{array}{l}
2)\\
a)\\
2C{H_3}COOH + Mg \to {(C{H_3}COO)_2}Mg + {H_2}\\
{n_{{{(C{H_3}COO)}_2}Mg}} = \dfrac{{14,2}}{{142}} = 0,1\,mol\\
{n_{C{H_3}COOH}} = 2{n_{{{(C{H_3}COO)}_2}Mg}} = 0,2\,mol\\
{C_M}C{H_3}COOH = \dfrac{{0,2}}{{0,25}} = 0,8M\\
{n_{{H_2}}} = {n_{{{(C{H_3}COO)}_2}Mg}} = 0,1\,mol\\
{V_{{H_2}}} = 0,1 \times 22,4 = 2,24l\\
b)\\
C{H_3}COOH + NaOH \to C{H_3}COONa + {H_2}O\\
{n_{NaOH}} = {n_{C{H_3}COOH}} = 0,2\,mol\\
{V_{{\rm{dd}}NaOH}} = \dfrac{{0,2}}{{0,5}} = 0,4l
\end{array}\)