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Under what conditions can $\ce{Na2O}$ be made from $\ce{NaCl}?$

I know $\ce{NaCl}$ doesn't oxidise under normal ambient conditions, but in the presence of what temperature and pressure ranges is this reaction possible?

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  • $\begingroup$ Maybe look at how sodium oxide is made in practice? $\endgroup$ – Oscar Lanzi Nov 23 '19 at 20:31
  • $\begingroup$ Sodium oxide is usually made from oxidation of pure sodium, however I am looking for a direct formation of sodium oxide from sodium chloride. $\endgroup$ – Joeseph123 Nov 23 '19 at 20:34
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    $\begingroup$ Methinks this ain't happening, or the method would already be in use. There must be some reason they trouble to use purified sodium. $\endgroup$ – Oscar Lanzi Nov 23 '19 at 20:36
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There is no need (or possibility, really, in terms of standard lab capabilities) to oxidize sodium(I). In fact, one method relies on sodium(I) reduction to metal as a method of eliminating unwanted chloride.

Method 1

  1. Electrolysis of molten sodium chloride: $$\ce{2 NaCl(l) -> 2 Na(l) + Cl2(g)}$$

  2. Oxidation of sodium metal to oxide by burning: $$\ce{4 Na + O2 ->[>\pu{250 °C}] 2 Na2O}$$ Drawback: pure sodium oxide cannot be obtained by direct oxidation of sodium. Instead, a mixture of sodium peroxide and sodium oxide is formed. In order to suppress the formation of peroxide, sodium metal or sodium nitrate is added in excess to the mixture in inert atmosphere: $$\ce{Na2O2(s) + 2 Na(l) ->[\pu{150 °C}] 2 Na2O(s)}$$

Method 2

  1. Convert sodium chloride to sodium bicarbonate using Solvay process: $$\ce{NaCl(aq, conc) + H2O(l) + NH3(g) + CO2(g) -> NaHCO3(s) + NH4Cl(aq)}$$

  2. Thermal decomposition of bicarbonate first yields in sodium carbonate: $$\ce{2 NaHCO3(s) ->[\pu{250 - 300 °C}] Na2CO3(s) + CO2(g) + H2O(g)}$$ which is subsequently calcined to form an oxide: $$\ce{Na2CO3(l) ->[>\pu{1000 °C}] Na2O(s) + CO2(g)}$$ This appears to be a preferred method as it is less energy- and resources-consuming and allows to obtain $\ce{Na2O}$ selectively.

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  • $\begingroup$ I agree this might be seemingly unnecessary practise, but this would help a bit with my research. Are there any direct ways to obtain the oxide from the chloride, without electrolysis? Possibly with the use of under-pressure or over-pressure with elevated temperatures? $\endgroup$ – Joeseph123 Nov 23 '19 at 22:05
  • $\begingroup$ I was wondering if the pressure is reduced from rtp to around ~0.1-0.2 atm this may aid in destabilising the sodium chloride crystal? $\endgroup$ – Joeseph123 Nov 23 '19 at 22:06
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    $\begingroup$ @Joeseph123 If you have a muffle furnace, then the second method is probably what you are looking for. Considering both sodium chloride and carbonate are equally very cheap, you may opt out conversion to hydrocarbonate and start from carbonate; this could save some time. And no, to affect the crystal lattice of ionic solids to a noticeable degree you need extreme pressures; reducing pressure a little won't do a thing, I'm afraid. $\endgroup$ – andselisk Nov 23 '19 at 22:10
  • $\begingroup$ In my case I am looking for a way that doesn't require the addition of another reagent. By any chance does alumina(Al2O3) react with NaCl? Alumina is of very high abundance, and a lot more accessible in my project. $\endgroup$ – Joeseph123 Nov 23 '19 at 22:36
  • $\begingroup$ @Joeseph123 But Al2O3 is another reagent? By smelting NaCl and Al2O3 I suspect you end up with NaAlCl4 or some oxochloride, judging from the related phase diagrams (AlCl3–NaCl; Na2O–Al2O3). Sorry, but it looks like you are over-complicating things that can be done much easier. Thermal decomposition of Na2CO3 is straightforward and there is no unwanted side-products. $\endgroup$ – andselisk Nov 23 '19 at 22:55

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