Animated Solution for Chemistry - s and p-Block Elements: One mole of magnesium nitride on reaction with an excess of water gives

Imagine you are in a chemistry lab, and you drop a piece of solid magnesium nitride into a beaker full of water. What exactly happens at the molecular level?

We are dealing with a classic inorganic reaction: the hydrolysis of a metal nitride. Magnesium nitride, an ionic compound, consists of magnesium ions and nitride ions. Water, on the other hand, can be thought of as a combination of hydrogen ions and hydroxide ions.

When these two meet, a double displacement-like process occurs. The highly electronegative nitrogen atoms are eager to grab hydrogen atoms from the water, while the magnesium atoms pair up with the remaining hydroxide ions.

Let's translate this chemical dance into a balanced equation. The skeletal reaction is simply magnesium nitride reacting with water to form magnesium hydroxide and ammonia gas.

Now, we must respect the law of conservation of mass. We have three magnesium atoms on the reactant side, so we must produce three molecules of magnesium hydroxide.

Similarly, we have two nitrogen atoms in our reactant, which means we will generate exactly two molecules of ammonia gas.

To supply enough hydrogen and oxygen for these products, we need exactly six molecules of water. The beautifully balanced equation looks like this:

With the balanced equation in front of us, the stoichiometry is crystal clear.

The coefficient in front of magnesium nitride is one, and the coefficient in front of ammonia is two. This means that one mole of magnesium nitride will always yield exactly two moles of ammonia gas upon complete hydrolysis.

There is absolutely no nitric acid formed in this process, as hydrolysis is not a redox reaction; the oxidation state of nitrogen remains at minus three throughout. Therefore, the correct answer is two moles of ammonia.