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Thermal Decomposition of Carbonates


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#1 Daave

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Posted 31 March 2005 - 09:00 AM

As we look at the metals on the periodic table, the further we go along, the more difficult that metal's carbonate is to decompose. i.e. Sodium Carbonate is more readily decomposed than Calcium Carbonate. I need to devise a method of experimentally testing this.

My thoughs as such are; we heat the carbonate (as a solid - possibly in water [but NOT aqueous]), and using limewater - test at what temperature carbon dioxide is released.

My question is - is this approach feasible, what equipment will I need, is there a better way of proving the hypothesis. I have access to varoius carbonates, limewater, and ordinary lab equipment (glassware, bunsens, filtration devices, etc)


Any suggestions? :)
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#2 raivo

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Posted 31 March 2005 - 09:38 AM

Sodium Carbonate is more readily decomposed than Calcium Carbonate.


Not true! Calcium carbonate decomposes at much lower temperatures. If you want to explore decomposition temperatures of carbonates you need very strong heating. I suppose that some alkali metal carbonates do not decompose even in bunsen burner flame.
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#3 Daave

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Posted 31 March 2005 - 10:10 AM

Not true! Calcium carbonate decomposes at much lower temperatures.

AH yes - I got it the wrong way round - the actual hypothesis I had to test experimentally is:

"that the ease of decomposition of carbonates is in the reverse order of the Periodic Table"

that being from easiest to most difficult, not the way around - as I had initially interpreted it.

When heating it (at such high temperatures), what would be the best way to collect the carbon dioxide let off? Or again - as I asked in my original post - is there some easier way to do it?
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#4 raivo

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Posted 31 March 2005 - 11:48 AM

If you can use analytical scales you may measure weight of remaining oxide instead of collecting CO2.

Some of carbonates can be decomposed in test tube. You have to put bent tube (usally glass is used, but when collecting CO2 metallic tubes are as good) through stopper and collect gas to flask or graduated cylinder that is capsized on water tank.
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#5 fermions

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Posted 31 March 2005 - 02:34 PM

I think that some carbonates don't decompose on heat e.g. sodium carbonate
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#6 jdurg

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Posted 31 March 2005 - 03:11 PM

Sodium carbonate will decompose upon heating. You have to be under the proper environment, however. (Performing the heating under a vacuum is the best way to accomplish this so that you can remove the CO2 as it is forming).
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#7 akcapr

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Posted 31 March 2005 - 03:16 PM

ive decomposed sodium carbonate before
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#8 budullewraagh

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Posted 31 March 2005 - 11:35 PM

well, we all have. CO3-2 --(H+)-->CO2

thermally, now that's different
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#9 Daave

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Posted 1 April 2005 - 07:33 AM

I do not need to prove that a carbonate will separate into it's oxide and carbon dioxide - but that the carbonates further down the periodic table are easier to decompose than those higher in the periodic table i.e. Calcium carbonate decomposing more easily than Sodium carbonate.
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#10 akcapr

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Posted 1 April 2005 - 07:57 PM

take some carbonate in a flaks/tuest tube. put a thermoter in ther and also have stopper draiwing the CO2 into lime water. then note the temperature at witch a precipetate forms. And heat its slowly for most accurate results.
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#11 fermions

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Posted 2 April 2005 - 02:45 PM

my teacher used to tell me sodium carbonate doesn't decompose on heat.... can the decomposition be achieved by a Bunsen flame? (if not I think that's why the teacher doesn't tell me the truth)
thanks
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#12 Daave

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Posted 2 April 2005 - 11:50 PM

Sodium carbonate decomposes somewhere above 851 degrees celcius.
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#13 BenSon

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Posted 3 April 2005 - 04:22 AM

my teacher used to tell me sodium carbonate doesn't decompose on heat



I was under the impression that every compound would decompose if enough heat was added...BTW your teacher sounds lost is he a PE teacher? :rolleyes:

~Scott
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#14 Daave

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Posted 4 April 2005 - 03:21 AM

agreed - definitely a lost P.E. teacher - BenSon is right, any substance will decompose given enough heat, the temperature at which this will occur is dependant on various things including the strength of the intra-molecular bonds and the distance of the valence electrons from the nucleus.
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#15 fermions

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Posted 4 April 2005 - 02:51 PM

I see... maybe it's so called out of syllabus at my level (even the public exam states the answer as cannot be decomposed) maybe I'll learn it at A level
Even the Haber process and Le Chaterlier's Principle are not required in my exams, I bet I'll learn more at A level
thanks anyway
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#16 YT2095

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Posted 4 April 2005 - 02:57 PM

IIRC the proces is called Calcination (the carbonate decomp thingy).
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