Question

When magnesium burns in air, compounds of magnesium formed are magnesium oxide and:
(A) \[M{g_3}{N_2}\]
(B) \[MgC{O_3}\]
(C) \[Mg{\left( {N{O_3}} \right)_2}\]
(D) \[MgS{O_4}\]

Answer 1

Hint: Try to recall that when magnesium ribbon is heated in air then it reacts both with oxygen and nitrogen present in air. Now, by using this you can easily find the correct option from the given ones.
Complete answer:
* It is known to you that alkaline earth metals like magnesium being less electropositive than alkali metals react with air slowly upon heating to form oxides and nitrides.
* When magnesium burns in air than magnesium burns with dazzling brilliance to form a mixture of magnesium oxide \[\left( {MgO} \right)\] which is a white solid and magnesium nitride \[\left( {M{g_3}{N_2}} \right)\] which is a greenish yellow powder.
* The reaction of magnesium with oxygen to form magnesium oxide is as follows:
\[2Mg + {O_2} \to 2MgO\]
The formation of magnesium oxide is an exothermic synthesis.
* The reaction of magnesium with nitrogen in air to form magnesium nitride is as follows:
\[3Mg + {N_2} \to M{g_3}{N_2}\]
The formation of magnesium nitride is an endothermic synthesis.
* Magnesium nitride reacts with water to produce magnesium hydroxide and ammonia gas.
The reaction of magnesium nitride with water to form magnesium hydroxide and ammonia gas is as follows:
\[M{g_3}{N_2}(s) + 6{H_2}O(l) \to 3Mg{\left( {OH} \right)_2}(aq) + 2N{H_3}(g)\]
* Magnesium oxide reacts with water to form magnesium hydroxide. The reaction of magnesium oxide with water to form magnesium hydroxide is as follows:
\[MgO(s) + {H_2}O(l) \to Mg{\left( {OH} \right)_2}(aq)\]
Therefore, from above we can easily conclude that option A is the correct option to the given question.

Note:
* It should be remembered to you that when magnesium hydroxide is heated, it gets decomposed into magnesium oxide and water vapour.
* Also, you should remember that magnesium powder or ribbon is used in flash powders and bulbs. A suspension of magnesium hydroxide in water (called milk of magnesia) is used as an antacid in medicine.