Đặt CT oxit là $Fe_xO_y$
$Fe_xO_y+2yHCl\to xFeCl_{2y/x}+yH_2$
Theo PT: $n_{Fe_xO_y}.x=n_{FeCl_{2y/x}}$
\(\to \dfrac{20x}{56x+16y}=\dfrac{40,625}{56+\dfrac{71y}{x}}\\ \to 1120x+1420y=2275x+650y\\ \to 1155x=770y\\ \to \frac{x}{y}=\frac{2}{3}\)
Vậy CT oxit là $Fe_2O_3$
