Dung dịch X gồm CuCl2 0,2M; FeCl2 0,3M; FeCl3 0,3M Cho m gam bột Mg

* Hướng dẫn giải

Đáp án C

$\begin{array}{l}+ n_{CuC{l}_2}=0,02 mol; n_{FeC{l}_2}=0,03 mol; n_{FeC{l}_3}=0,03 mol.\\ + Tính oxi hóa: F{e}^{3+}>C{u}^{2+}>F{e}^{2+}.\\ \bullet \mathrm{TH}1: \mathrm{T} gồm F{e}_2{O}_3, MgO\\ \left\{\begin{array}{l}BTE: 2\underset{x}{\underbrace{n_{Mg}}}=\underset{0,03}{\underbrace{n_{F{e}^{3+}}}}+2\underset{0,02}{\underbrace{n_{C{u}^{2+}}}}+2\underset{y}{\underbrace{n_{F{e}^{2+} p¨o}}}\\ m_T=40\underset{x}{\underbrace{n_{MgO}}}+160\underset{0,03-0,5y}{\underbrace{n_{F{e}_2{O}_3}}}=5,4\end{array}\right.\Rightarrow \left\{\begin{array}{l}x=0,055; y=0,02\\ m_{Mg}=1,32\end{array}\right.\\ \bullet \mathrm{TH}2: \mathrm{T} gồm CuO, F{e}_2{O}_3, MgO\\ \left\{\begin{array}{l}BTE: 2\underset{x}{\underbrace{n_{Mg}}}=\underset{0,03}{\underbrace{n_{F{e}^{3+}}}}+2\underset{y}{\underbrace{n_{C{u}^{2+} p¨o}}}\\ m_T=40\underset{x}{\underbrace{n_{MgO}}}+160\underset{0,03}{\underbrace{n_{F{e}_2{O}_3}}}+80\underset{0,02-y}{\underbrace{n_{CuO}}}=5,4\end{array}\right.\Rightarrow \left\{\begin{array}{l}x=0,055\\ y=0,04 (vô lý)\end{array}\right.\end{array}$