My textbook says that the decarboxylation of sodium acetate with sodalime produces methane. But if we replace sodalime with barium oxide, pure methane is produced.

What is the difference between pure methane and the methane produced in the first case?

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    $\begingroup$ maybe percentage of other products is less with barium $\endgroup$ – Black Jack 21 Feb 18 '17 at 11:42
  • $\begingroup$ if that were the case, it would have said that the yield of methane is more. $\endgroup$ – Abhishek Mhatre Feb 18 '17 at 11:43

The first reaction is:

$$\ce{CH3COONa + NaOH -> Na2CO3 + CH4}$$

According to Encyclopedia of Inorganic Chemistry vol. 2:

The obtained methane in this process is not pure and may contain as much as 8 % hydrogen and 10% other hydrocarbons such as the chloride (to remove acetylene) and concentrated sulfuric acid (to remove ethylene and moisture). The purified methane still contains hydrogen, which may be removed as water by boiling at 110 °C the excess oxygen is absorbed concentrated sulfuric acid.

The second reaction doesn't make much sense to me with $\ce{BaO}$. If this reaction is happening in an aqueous medium, then $\ce{BaO}$ would probably have reacted to form $\ce{Ba(OH)2}$*. So I think you could justify representing the second reaction as:

$$\ce{CH3COONa + Ba(OH)2 -> CH4 + NaCO3 + BaCO3}$$

This is also how the aforementioned book represents the reaction, stating:

Heating sodium acetate with barium hydroxide, instead of sodium hydroxide forms nearly pure methane:

Sodium Acetate + Barium Hydroxide $\rightarrow$ Methane + Sodium Carbonate + Barium Carbonate

$$\ce{CH3COONa + Ba(OH)2 -> 2CH4 + NaCO3 + BaCO3}$$

So I guess the increased purity, in this case, is just due to the different amount of other products produced during the reaction.

| improve this answer | |
  • $\begingroup$ BTW, the first paragraph you quote seems really horribly written, to the point of incomprehensibility. The last sentence isn't even grammatical (there seems to be something missing after "110 °C" and/or after "absorbed") and the first one isn't much better. I suspect there was an editing mistake of some kind, and that the paragraph is indeed missing some text. $\endgroup$ – Ilmari Karonen Feb 18 '17 at 15:15
  • $\begingroup$ Seems that way. The quote is from page 390. There seems to be other errors on the page as well, but nothing so severe that I wouldn't trust the main idea behind the text, which is that the latter reaction produces a better yield of methane. $\endgroup$ – Bdrs Feb 18 '17 at 15:23
  • $\begingroup$ Actually, I found a copy of the book on archive.org (not sure if it's legal or not, hence I'm not linking to it), and the whole book seems to be full of similarly broken English. :( If that's the textbook the OP is using, I feel sorry for them. $\endgroup$ – Ilmari Karonen Feb 18 '17 at 15:24
  • $\begingroup$ I'm using a different book-OP Tandon. $\endgroup$ – Abhishek Mhatre Feb 18 '17 at 16:00

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