Hello I’m stuck with this Quesition : When & why is water added to the crucible

Question

Hello I’m stuck with this Quesition :
When & why is water added to the crucible and why is it added ?
I provided a picture of the paragraph that has the answer
So adding the water results in mg sulfide & releases ammonia gas ???
Does this happen after it’s cooled down ? The paragraph has left me a little confused
Please help me thank you for your time . crucible and cover are fired to red heat in order to burn off impurities in the crucible and nesablish a constant weight. o. aicgested periods for heating and cooling are general guidelines. More important, the metal e heated long enough for complete conversion to the oxide. The crucible should be cooled ntly to avoid a buoyancy error at the balance ring magnesium in air produces magnesium nitride in addition to the magnesium oxide. Adding isilled water to the crucible contents decomposes magnesium nitride and releases ammonia gas. (The crucible contents fizz, and the odor of ammonia gas may be noticeab contents converts magnesium hydroxide to magnesium oxide. If the magnesium metal has reacted completely, there will be no small sparks observed when the crucible cover is lifted .We will assume that the copper wire has reacted completely when there are no longer any traces of weight. veiuh for yellow-brown) sulfur in the crucible. If there is any doubt, heat the crucible to constant 0.00625 = cao the balance causes a buoyancy effect, and mass readings will be low.

Explanation / Answer

Ans. It’s assumed that the aim of experiment to determine the empirical or chemical formula of magnesium oxide, or similar experiment where molar rations of Mg and O in the compound is accounted.

#1. Mg is highly reactive. There is 78% N2 and 21% O2 in air. Mg reacts both with N2 and O2 when temperature of the metal is very high (800.00C or above) during oxidation in air.

            Mg + Air -----------> MgO (s) + Mg3N2(s)

Since you aim is to determine the (Mg : O) molar ratio, the formation of Mg3N2 is undesirable. In the resultant mixture, there are both the solids of MgO and Mg3N2 in random proportion (i.e. the ratio of MgO and Mg3N2 is not constant when the experiment is repeated).

#2. So, is becomes inevitable to convert Mg3N2 into MgO so that all the metal is present in the form of metal oxide. This conversion is done in two steps after the crucible has cooled down after initial oxidation step-

            I. Mg3N2 + H2O ------> Mg(OH)2 + 2 NH3(g)

When treated with distilled water, magnesium nitride forms Mg(OH)2 and NH3. The ammonia gas instantly escapes the liquid with a fizz sound.

            II. Mg(OH)2 -----Heat-------> MgO + H2O

When Mg(OH)2 is heated, it’s converted into MgO. The resultant water can be evaporated to obtain pure metal oxide.

# So, the purpose of addition of distilled water to magnesium nitride is to transform it into metal oxide- the aim of you experiment.

* You would then calculate the increase in mass of oxidized metal with respect to the pure metal (element). So, you further calculate the mass and moles of O2 consumed to form metal oxide. The information is further used to determine the empirical/chemical formula of magnesium oxide or as desired.

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