Make up the equations of chemical reactions: a) Mg – MgO – MgCl2 b) Na2O – NaOH – Na3Po

1. The chain of transformations.
a) 2Mg + O2 = 2MgO.
MgO + 2HCl = MgCl2 + H2O.

b) Na2O + H2O = 2NaOH.
3NaOH + H3PO4 = Na3PO4 + 3H2O.

2. Solution of the problem.

FeO + 2HCl = FeCl2 + H2O.
From the coefficients of the equation we obtain
n (HCl) = 2 * n (FeO) = 0.2 mol
n (FeO) = n (FeO) = 0.1 mol

The mass is determined from the amount of substance and molar mass:
m (HCl) = n (HCl) * M (HCl) = 0.2 * 36.5 = 7.3 g.
n (FeO) = n (FeCl2) = 0.1 mol.
m (FeCl2) = n (FeCl2) * M (FeCl2) = 0.1 * 127 = 12.7 g.