[Enthalpy]

Can you compute how many moles of CO₂ are needed to bring 1L bottle volume from 1atm to 2atm, once the temperature settles to the Ocean's temperature?
https://en.wikipedia.org/wiki/Ideal_gas_law

Then, 1 mol of bicarbonate releases 1mol of CO₂. I believe it also takes 0.5 mol of citric acid. Can someone confirm this please? pK_a 3.13, 4.76 and 6.39.

Maybe you can check Wiki's pages
https://en.wikipedia.org/wiki/Sodium_bicarbonate
https://en.wikipedia.org/wiki/Citric_acid
(and tartaric acid if you can buy some. It should need less mass than citric acid)
and find the mass for one mole of each.

Then you can deduce the mass of acid for the bottle's volume, and a minimum mass of bicarbonate. I'd put some little excess of bicarbonate, less harmful to the plastic than excess acid.

A water amount must still be estimated.

[AWK]

pK_a2 of carbonic acid - 10.3

[EDsteve]

It's all new territory for me. But i will give it a try:

This website told me the Volume of 1 mole of CO2 at room temp and pressure:
https://sciencing.com/calculate-volume-co2-7868589.html
So 1 mole CO2 needs a volume of 24 liter at room temperature.

This website lets me calculate the density of moles in relation of pressure:
https://socratic.org/chemistry/the-behavior-of-gases/molar-volume-of-a-gas-224-l-at-stp
So i took the formula in the attachment and changed temperature to 300K (lake temperature) and the pressure to 2 atm.
So that means for my understanding: 1 mole CO2 has a Volume of 12,3 Liter at 300K and 2 atm pressure.

So if i have a 1,5l bottle: 1,5 / 12,3 = 0.122

That means i need 0.122 moles of CO2 to create a pressure of 2 atm in a 1,5l bottle.

And this nice online converter converts mole to gram:
https://planetcalc.com/6777/

So according to my (for sure wrong) calculation i need 2,2g baking powder and 12g citric acid. Does that sound right to you?


The amount of water needed depends on the solubility of the two "ingredients" right?
Sodium bicarbonate: 100 g/L (at 25degrees) -> I need 22ml water to dissolve 2,2g baking powder
Citric Acid: 64.3% w/w  (at 25degrees) -> I need 20ml to dissolve 12g Citric Acid

So would 22ml do the job? Or do i have to add 20ml plus 22ml?

Thanks for all your help. I really appreciate it.



P.S.: Tartaric acid is ten times the price. But if the needed amount is a lot less. Then worth it. Because it also needs a lot less water to dissolve too.

[Borek]

That means i need 0.122 moles of CO2 to create a pressure of 2 atm in a 1,5l bottle.

Yes.

So according to my (for sure wrong) calculation i need 2,2g baking powder and 12g citric acid. Does that sound right to you?

Unfortunately you are right - this is wrong. Hard to say why. You need more sodium bicarbonate but less citric acid (although using some excess is a good idea.

Trick is, baking powder is not pure bicarbonate, so you will probably need more.

[EDsteve]

Okay. Cool. That already gives me some numbers i can start with. Of course i will start with half of that. Just to see what happens and then go from there.

Another question i am not sure about:

Sodium bicarbonate is baking soda and not baking powder. So i should use baking soda instead of baking powder?

Correct me if i am wrong

[billnotgatez]

...
Sodium bicarbonate is baking soda and not baking powder. So i should use baking soda instead of baking powder?
...

Correct
According to WIKI baking powder can be baking soda with added ingredients.
You want the plain baking soda.

[Enthalpy]

This is how I imagine the process:

• Bottle is full of air at 1 atm
• Bicarbonate and acid are poured in, in proper amount
• Stopper is closed, pressure rises to 2atm

So CO₂ must provide only 1atm in 1.5L, or equivalently, only 0.75L at 2atm, as air provides the rest for free. That is, only 0.06mol CO₂ are necessary.

Exegesis by AWK-logists suggests that 1 mol citric acid frees 3 mol CO₂, not 2, because citric acid acts by all its three functions. Less citric acid needed. Hope I grasped it properly, I never needed such a thing for rocket engines.

One 150g mole of tartaric acid frees 2 moles of CO₂. One 192g mole of anhydrous citric acid frees 3 moles of CO₂.

Amount of water: if the acid and the bicarbonate are first dissolved separately, then the solutions poured in the bottle, solubilities apply. A bit excess water helps dissolve.

The presently estimated water amount has no big drawback, does it? It only reduces the buoyancy of the bottle. I suppose it can be seawater, just try.

Alternately, fine powders of bicarbonate and acid could be mixed dry, introduced in the bottle, and water be added. This might accept less water, or not, difficult to predict. I don't see clear advantages to this. Maybe the reaction is slower, giving time to close the stopper and get away, useful.

Please take some precautions before the first trial and during the production. While a soda bottle is not a grenade, I know by experience it makes a strong bang, and among thousand bottles, some will explode. Do it outdoors. Protect your ears. Maybe a scuba mask protects your eyes against debris, and skiing gloves protect your hands, but maybe not, I don't know. I would leave the bottles behind a wall or sandbags immediately after closing the stopper. Use a mirror on a boom to watch if bubbling is finished.

[EDsteve]

Thanks for your infos.

Yesterday Citric acid and baking soda arrived so i had the chance to play around a bit.

I have done only tests with 5 different mixtures for now. And for now i get pretty good results with 7g citric and 7g baking soda plus 15ml water.

The trick is to keep the bottle almost horizontal at around 15 degrees. Water first which runs to the bottom and then the powder mix with a narrow spoon which stays on the upper half. So the water and the powder does not mix right away-> Close the lid and then give it a quick shake.
Otherwise i will loose most of the pressure because the reaction happens pretty quickly.

Unfortunately these caps from the not-soda-bottles are very sensitive. The threshold between overturn and a tight seal is very small. So i had some difficulties with that... leaks etc... But a total pressure of 1,5atm should actually do it.

Will do more testing tomorrow again with my full face snorkeling mask

I will post my final results here when i am satisfied.

The presently estimated water amount has no big drawback, does it? It only reduces the buoyancy of the bottle. I suppose it can be seawater, just try.

Yes. Correct. So if i need 15ml for each bottle. That means i will loose around 1% buoyancy which is totally worth it because i will gain maybe 30% buoyancy because of the internal pressure.
BTW: i live at a lake

[Enthalpy]

Please protect also your hands and arms. Just a water bottle isn't so horrible, but you don't need to hurt yourself.

Nice idea, introducing separately the powder and the water. Better than pouring the water just before shutting the bottle. But over 1000 bottles, you will definitely make mistakes.

[...] I will gain maybe 30% buoyancy because of the internal pressure. [...]

As a child, I wanted to pump pressurized air into boats so they could carry more load. No adult around me could correct that.

As opposed, a vacuum aerostat is vaguely suggested there
http://www.physicsforums.com/showthread.php?t=524229
http://www.physicsforums.com/showthread.php?p=4121567#post4121567
http://www.physicsforums.com/showthread.php?t=647031
pretty much useless, an endeavour for good mechanical designers. Not because it's easy, but because it's difficult.

[EDsteve]

Yes. I use gloves and snorkeling mask. But it's kind of difficult to make a bottle explode. Of course i also tried it out of curiosity and failed. The cap of the non-soda bottles will release pressure before anything happens. And the soda bottles. They need 10 times of the mix. So i think that project is pretty safe.

Another question: The transparent liquid which is the end result in the bottles. Is that still harmful?

As a child, I wanted to pump pressurized air into boats so they could carry more load. No adult around me could correct that.

As mentioned in my first post. I am adding the pressure to protect the bottles from getting squeezed under water. So if they keep their volume instead of getting squeezed. That's my 30% increase of buoyancy.
I am well aware that volume (displacement) is the key of buoyancy and not what is inside. Well... not really accurate because if steel would be inside. It will sink  And adding air would actually make it more heavy too = worse
I still like the vacuum balloon idea from the links

[Borek]

The transparent liquid which is the end result in the bottles. Is that still harmful?

Not more than the bicarbonate nor citric acid themselves (actually even a bit less) - I would not bath in them nor eat/drink them, but other than being possibly a mild irritants they are all reasonably safe.

[Enthalpy]

[...] it's kind of difficult to make a bottle explode. Of course i also tried it out of curiosity [...]

Somehow I had guessed you would.

It wouldn't hurt to recompute cleanly the amounts of bicarbonate and acid, in order to save them and to limit the produced pressure. There was a bug in the 1+1atm computation.

[Ren]

I totally love this experiment, EDsteve.:-) How did it go? Did you manage to pressurize some significant number of the bottles to actually build something?

[EDsteve]

Hey Ren,

yap. The idea sounds great
But it should be also worth it. And according to my calculations i can't do it with acid and baking powder because the shipping costs here in Indonesia will make it too expensive.
I pressurized around 80 bottles already but i am thinking to use fermentation in future. Yeast can basically be made for free. So only sugar is needed which i can find at the next shop. It will also be easier and faster to add the indigence in the bottles because the process is very slow.

But i have the problem to start too many projects at the same time. So the progress is sloooow 

I will keep this thread updated if there is an update

P.S.: Not-Soda-bottles can still hold a good amount of pressure but maybe 5-10% don't. That's another lesson i learned.

[Enthalpy]

For the same ΔP*V, the shipped mass is smaller with dry ice (it's CO₂). You can conserve it for weeks in polystyrene foam. Find something (with paper?) that gives you time to close the bottle before contact with the walls evaporates the ice.

Liquid nitrogen would be even lighter. Maybe it's less available than dry ice. More difficult to introduce in the bottle with delayed evaporation. Aluminium foil maybe.

If you live in a remote location without dry ice nor electricity, make your earning of delivering dry ice for fridges.