Gọi halogen cần tìm là X
\(n_{MgX_2}=\dfrac{19}{24+2.M_X}\left(mol\right)\)
\(n_{AlX_3}=\dfrac{17,8}{27+3.M_X}\left(mol\right)\)
PTHH: Mg + X2 ---> MgX2
\(\dfrac{19}{24+2.M_X}\)<-\(\dfrac{19}{24+2.M_X}\)
2Al + 3X2 --> 2AlX3
\(\dfrac{17,8}{18+2.M_X}\)<-\(\dfrac{17,8}{27+3.M_X}\)
=> \(\dfrac{19}{24+2.M_X}=\dfrac{17,8}{18+2.M_X}\)
=> MX = 35,5 (g/mol)
=> X là Cl (Clo)
\(n_{Cl_2}=\dfrac{19}{24+2.35,5}=0,2\left(mol\right)\)
=> mCl2 = 0,2.71 = 14,2 (g)