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Is magnesium nitride formed in the combustion of magnesium?

wallpapers Products 2021-04-14
Sometimes errors show up in textbooks and spread like memes. Unfortunately, textbook authors generally believe that the previous article was correct and that the facts no longer need to be checked. In the case of magnesium strips burning in the air, the "fact" that a mixture of magnesium oxide and magnesium nitride is formed has become "common sense" and never seems to be questioned.
This experiment was conducted and supervised many times and no evidence of nitride formation was ever seen. A review of the literature and some experiments showed that no significant amounts of nitrides were formed.
The magnesium band heating method to determine the composition of magnesium oxide is a popular chemical experiment in high school and college freshmen. A known amount of magnesium strip is heated over a gas flame in a partially covered crucible. Mg reacts with O2 in the air, leaving a white residue of MgO. The partially opened crucible lid slows down the burning rate of Mg and reduces the loss of MgO as smoke. Knowing the masses of Mg and MgO can determine the stoichiometry of the reaction.
In each description of this experiment that we have seen, the crucible is heated until the reaction appears to be complete, about 5-10 minutes, and cooling is allowed. A few drops of water were added to hydrolyze any Mg3N2 that might form, then the crucible was reheated to remove the water and any Mg(OH)2 was decomposed into MgO and H2O. After cooling again, weigh the crucible.
The cooling-hydrating-reheating process makes the experiment considerably more difficult. Even college students can lose products or break cauldrons by adding water too early or heating it too strong while the cauldrons still contain wet products. Removing this step will make the experiment more robust and easier to perform.
Magnesium nitride is usually described as yellow, and none of us have ever seen the yellow residue after the first heat. Students will usually notice that there is no yellow product and either ask or silently skip the second step, with no significant result drop.The question then is whether nitrides have ever been formed.
In this aspect of the study, we found that even in advanced textbooks there is disagreement about some physical properties of Mg3N2. For example, it is described as colorless, 1, 2 yellow-green, 3 yellow-green, yellow-orange, and yellow5, while Bickley and Greg6 describe both gray and yellow. In addition, various melting or decomposition points are given.Belin7 noticed that when Mg reacted in N2, it reacted preferentially with a trace amount of O2.
However, it is agreed that Mg3N2 can be synthesized by direct reaction of elements, and it is agreed that lab-scale reactions can be completed in 4-5 hours at 800-850 ° C.Interestingly, Durrant2 notes that Mg in liquid N2 "burns beautifully."

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