What mass of aluminum is needed for recovery 56g. iron from iron scale Fe3O4 by the method of aluminothermy?

To solve the problem, let’s compose the reaction equation:
3Fe3O4 + 8Al = 9Fe + 4Al2O3 – redox reaction, obtained iron and aluminum oxide;
Let’s make calculations using the formulas:
M (Al) = 26.9 g / mol;
M (Fe) = 55.8 g / mol;
Let us determine the amount of moles of iron, if its mass is known:
Y (Fe) = m / M = 55 / 55.8 = 1 mol;
Let’s make the proportion:
1 mol (Fe) – X mol (Al);
-9 mol – 8 mol from here, X mol (Al) = 1 * 8/9 = 0.88 mol;
Let’s calculate the mass of aluminum by the formula:
m (Al) = Y * M = 0.88 * 26.9 = 23.9 = 24 g.
Answer: 24g.