if Mg3N2 is not completely decomposed, will experimental mole ratio of Mg to O be too low or too high?

Question

it is given that there the air is composed of 78% nitrogen and 22% oxygen, so inevitably, some magnesium nitride will form during the oxidation of a strip of magnesium ribbon. but if not all the magnesium nitride is decomposed, then will the mole ratio of Mg to O be too high or too low and why?

Answer 1

When magnesium reacts with oxygen gas:
2 Mg + O2 ---> 2 (MgO) the ratio of Mg to O is 1:1
(1 mole of Mg reacted produces 40.3 g of MgO)

When it reacts with nitrogen gas
3 Mg + N2 ---> Mg3N2 the ratio of Mg to N is 1: 0.67
(1 mole of Mg reacted gives 33.6 g of Mg3N2)

So if some Mg3N2 gets left behind in what you think is pure MgO, then the mass will be lower than it should be. Your calculated mass of oxygen reacted will be lower than it should be, too.

When you convert to moles, you will have fewer moles of oxygen
than you should have, i.e., the ratio of Mg to O will be too high.

Answer 2

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