Đáp án đúng: B
53,6.
$\displaystyle \begin{array}{l}\text{F}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\text{+8HCl}\xrightarrow{{}}\text{FeC}{{\text{l}}_{\text{2}}}\text{+2FeC}{{\text{l}}_{\text{3}}}\text{+4}{{\text{H}}_{\text{2}}}\text{O}\\\,\,\,\,\,\text{x }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\!\!~\!\!\text{ }\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{2x}\end{array}$
$\displaystyle \begin{array}{l}\text{Cu+2FeC}{{\text{l}}_{\text{3}}}\xrightarrow{{}}\text{CuC}{{\text{l}}_{\text{2}}}\text{+2FeC}{{\text{l}}_{\text{2}}}\\\,\text{x }\,\,\,\,\,\,\,\,\,\text{2x}\end{array}$
Chất rắn còn lại chắc chắn là Cu
=> mphản ứng $\displaystyle \text{=232x+64x=50-20,4}$
$\displaystyle \Rightarrow \text{x=0,1}\,\text{mol}$
$\displaystyle \Rightarrow {{\text{m}}_{\text{Cu}\left( \text{X} \right)}}\text{=50-232}\text{.0,1=26,8g}$
$\displaystyle \Rightarrow {\scriptstyle{}^{\text{o}}\!\!\diagup\!\!{}_{\text{o}}\;}{{\text{m}}_{\text{Cu}\left( \text{X} \right)}}\text{=53,6}{\scriptstyle{}^{\text{o}}\!\!\diagup\!\!{}_{\text{o}}\;}$
