- Phản ứng:  $F{{e}_{3}}{{O}_{4}}+8HCl+Cu\xrightarrow{{}}3FeC{{l}_{2}}+CuC{{l}_{2}}+4{{H}_{2}}O$

          mol:     0,08      0,6     0,12                                          

            dư:     0,005      0      0,045

Þ${{m}_{\text{r }\!\!{\scriptscriptstyle 3\!/\!{ }_4}\!\!\text{ n kh }\!\!\ll\!\!\text{ ng tan}}}=232{{n}_{F{{e}_{3}}{{O}_{4}}(d)}}+64{{n}_{Cu(d)}}=4,04\,(g)$