Why is water added to convert magnesium nitride to magnesium oxide, and what effect does this have on the MgO?

Question

Please explain.

Answer 1

The water provides the Oxygen for the oxide formation.

The first step is:

Mg3N2 + 6 H2O --> 3 Mg(OH)2 + 2 NH3

Mg(OH)2 is called Magnesium hydroxide which is commonly known as Milk of Magnesia. When heated, this compound loses water to give Magnesium oxide:

Mg(OH)2 --> MgO + H2O

This last reaction can also go the other direction, using water to hydrate the Magnesium oxide to give Magnesium hydroxide:

MgO + H2O --> Mg(OH)2