Thermal decomposition of calcium carbonate.

[macro2008]

In general, we heat CaCO3 to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas:

 

CaCO3 →825°C→ CaO + CO2

 

Is it possible to heat the calcium carbonate at temperatures below 825 degrees Celsius

[Sensei]

Why don't you make experiment by yourself?

 

Chalk you can buy in any stationery shop for penny.

 

That's CaCO3:

 

When we will use chalk as electrode in electrolysis it will become very hot in a few seconds and start to smoke white with nasty smelt and sparks will show up on it.

[John Cuthber]

Why don't you make experiment by yourself?

 

Chalk you can buy in any stationery shop for penny.

 

That's CaCO3:

 

When we will use chalk as electrode in electrolysis it will become very hot in a few seconds and start to smoke white with nasty smelt and sparks will show up on it.

Sensei,

Have you any idea what you are talking about?

I ask because

Most blackboard "chalk" is actually calcium sulphate.

Calcium carbonate is an electrical insulator, so it's not going to work as an electrode.

Carbon dioxide doesn't smell much.

 

 

Macro,

yes, you can get it to decompose at lower temperatures but the reaction is slow.

It would work better in a vacuum chamber.

The temperature given (825C) is the temperature at which the equilibrium pressure of CO2 is 1 atmosphere.

It's a bit like saying if you want to remove water from something, you can boil it off at 100 C.

But even at lower temperatures, it will still dry out.

The difference is that , you need to get the carbonate fairly hot before the decomposition happens at any noticeable rate.

(at room temperature, it doesn't happen at all)

[Sensei]

Sensei,

Have you any idea what you are talking about?

 

I am talking about mine experimentally gained experience.

Before posting, I have even repeated experiment.

 

You can see there is nothing in between electrode from chalk stick and water:

 

Bubbles of Hydrogen on negative electrode.

Quite small amount, because current is low 70 mA (above photo) to 0.13 A (below photo).

After adding 5 g of NaCl to water (~1 L), current goes to 0.5 A with distance between them like on above photo:

 

 

For a while, chalk stick is getting hotter and hotter and starts emitting white fume. Odor is absolutely not equal to SO₂/SO₃.

 

I have tried different metals which are connected with chalk stick, when I was doing it the first time years ago, and fumes were independent from used metal (if I recall aluminum, steel and copper).

For sure metals are going into reaction with chalk stick, there are evidences of this on surface.

 

I have made video of the whole experiment (even three times, because the first attempt was over 2 MB), but SFN refused .mp4 movies (2 MB was enough to have just 43 seconds..)

 

I ask because

Most blackboard "chalk" is actually calcium sulphate.

"most" doesn't mean "all".

 

I am pretty sure that mine chalks are made of CaCO₃, because I have used them to perform:

 

 

CaCO₃ -> CaO + CO₂

and then

CaO + H₂O -> Ca(OH)₂

 

 

The all sources in mine native language mention CaCO₃ as material for blackboard chalk sticks.

And only source mentioning CaSO₄ are in English language.

Maybe simply we are using different material for them in different countries.. ?

In UK majority CaSO₄, while here we're making them with CaCO₃.. ?

 

Quote from

http://en.wikipedia.org/wiki/Blackboard#Chalk_sticks

 

"A blackboard (UK English) or chalkboard (US English; also blackboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate,"

"Sticks of processed "chalk" are produced especially for use with blackboards in white and also in various colours.

These are often made not from chalk rock but from calcium sulfate in its dihydrate form, gypsum.

Chalk sticks containing calcium carbonate typically contain 40-60% of CaCO3"

 

(open question what's the rest 40-60%)

 

How about performing by yourself some experiments?

Put your chalk sticks to HCl.

If you will have CO₂ bubbles, you will know it's made of CaCO₃ (at least to some extent)..

Measure volume of produced CO₂ and you will know initial concentration of CaCO₃ (if there was any)..

 

 

Calcium carbonate is an electrical insulator, so it's not going to work as an electrode.

It's insulator when it's dry.

 

Any insulator can become electric conductor. It's just a matter of voltage.

http://en.wikipedia.org/wiki/Breakdown_voltage

 

Carbon dioxide doesn't smell much.

Yes, I know. I am using it in the cloud chamber particle detectors all the time..

Edited February 11, 2014 by Sensei

[Sensei]

I found a way to work around - zip it..

Chalk electrolysis 2.zip

 

 

[imatfaal]

I found a way to work around - zip it..

Chalk electrolysis 2.zip

 

 

People are gonna be loath to download a zipped file from the net - why not just put the video up on youtube or vimeo, even flickr and picassa accept vids now I think.

[Sensei]

People are gonna be loath to download a zipped file from the net - why not just put the video up on youtube or vimeo, even flickr and picassa accept vids now I think.

 

When I will buy new Full HD camera I will record new high quality video of these experiments and post. I promise.

It was taken quickly using phone at night just to show John.

Edited February 11, 2014 by Sensei

[John Cuthber]

"You can see there is nothing in between electrode from chalk stick and water:"

And, it's the water that conducts the electricity.

Thanks for proving my point.

 

""most" doesn't mean "all"."

 

At least I said "most" while you said that "any" stationers' chalk is the carbonate.

 

"Chalk you can buy in any stationery shop for penny."

Again, thanks for illustrating my point.

"The all sources in mine native language mention CaCO₃ as material for blackboard chalk sticks.

And only source mentioning CaSO₄ are in English language."

So the ones that are in the same language as the OP's question have a good chance of referring to...

 

 

"Any insulator can become electric conductor. It's just a matter of voltage."

indeed, but once you are talking about dielectric breakdown you are no longer talking about electrolysis .

So, once again, thanks for illustrating my point.

 

 

I can't see how the video will help.

Edited February 11, 2014 by John Cuthber