When burning magnisum need to add water to eliminate MgN or can the emprical formula still be found w. it?

Question

ok so i have a lab where after you are done heating the magnism in the crucible and it is done reacting, it says you are suposed to use water to wash out the MgN and then boin the water away to help find the emprical formula of MgO. is adding the water and boiling it away nessary for the lab? or can it be left out and it wont make a difference?

i forgot to add the water in my orignal experiment and for my lab i have to prove that using the water isnt nessary. and toy can still come close to the right answer even though a step was left out.

it says that the water is to decmpose the MgN. so is the water still necessary?

Answer 1

You aren't really washing out the magnesium nitride:

Magnesium nitride decomposes in water to form magnesium hydroxide, which when heated converts to magnesium oxide.

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

Mg(OH)2 + heat ----> MgO + H2O

However, magnesium nitride is listed as decomposing at 800 C (presumably to the individual elements), in which case, the Mg will convert to MgO (since you're heating it in air). So, I suspect there will be little difference in running the experiment either way.

Added:

Whether the water step is necessary or not would depend on how much Mg3N2 actually forms from Mg burning in air and how accurate of an answer for calculating the formula for MgO you need. Since you really just need to tell whether the empirical formula is MgO vs Mg2O or Mg2O3 or MgO2 etc it doesn't need to be "right on the button". Why don't you just do the calculation and see if you get MgO for the empirical formula; that would be the best evaluation whether the water step is actually needed or not.

Answer 2

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Answer 3

Magnesium nitride is probable a a salt , adding water and boiling after the water only remove the water in the first place. the MgN will recrystallize , so adding the water will not remove therefore it is unnecessary.