gatewaycityca
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How cold could you get vinegar and baking soda?
Okay...how about something different. What about getting something cold from a chemical reaction? I've read that the reaction between
vinegar and baking soda is endothermic so it gets colder. I never really noticed that before, but I did a simple experiment by just mixing them into a
cup and I kept adding more baking soda and vinegar. Sure enough, it did seem to get quite a bit colder to the touch. (I haven't actually measured it
with a thermometer yet, but I've seen videos where other people have, and there was a pretty significant temperature drop.)
Well, I wanted to try a simple experiment. Let's say you have two metal containers, one a little bigger than the other. Put the smaller container
inside the larger one. If you filled the larger one with water, and then mixed baking soda and vinegar in the smaller one, the reaction would try to
draw heat from its surroundings. So it should draw heat from the water surrounding it. If you were to keep adding fresh baking soda and vinegar into
the smaller container (like maybe dumping it out and replacing it once it stopped reacting) so that each successive reaction would keep drawing heat
from the water, how cold could you get the water? Would it be possible to actually get the water to freeze, or get near freezing temperature?
I was just curious. It seems like, if the reaction wants to draw heat from its surroundings each time, it should make the water pretty darn cold
eventually.
I know, vinegar and baking soda is the oldest trick in the book....but I don't remember ever seeing anyone try this. I mean, exactly how cold
could you get it?
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blogfast25
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Quote: Originally posted by gatewaycityca  | Well, I wanted to try a simple experiment. Let's say you have two metal containers, one a little bigger than the other. Put the smaller container
inside the larger one. If you filled the larger one with water, and then mixed baking soda and vinegar in the smaller one, the reaction would try to
draw heat from its surroundings. So it should draw heat from the water surrounding it. If you were to keep adding fresh baking soda and vinegar into
the smaller container (like maybe dumping it out and replacing it once it stopped reacting) so that each successive reaction would keep drawing heat
from the water, how cold could you get the water? Would it be possible to actually get the water to freeze, or get near freezing temperature?
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Remember that heat flows ONLY from a hotter to a colder body. Only if your bicar/vinegar body can reach to below 0 C could you freeze the surrounding
water, no matter how many successive reactions you carry out. You can only keep pumping heat out of the second body as long as the first one is colder
than the second one.
[Edited on 14-2-2014 by blogfast25]
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vmelkon
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My guess is -20 °C or something in that range. From what I remember from chemistry class a long time ago, every increase by 10 degrees double the
rate of reaction as a rule of thumb. So, the rate of reaction between the vinegar and sodium bicarbonate will go down.
It is possible to freeze water with other reactions. For example, dissolve NH4Cl into water or add solid NH4Cl to Ba(OH)2 and mix hard. So, any
endothermic reaction will do as long as it sucks enough kJ from the water.
[Edited on 14-2-2014 by vmelkon]
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blogfast25
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| Quote: Originally posted by vmelkon | So, any endothermic reaction will do as long as it sucks enough kJ from the water.
[Edited on 14-2-2014 by vmelkon] |
Not really, as explained above. To reach zero the endothermic reaction has to reach below zero.
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MrHomeScientist
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Instant cold packs, as their name might suggest, are also great at chemically lowering temperatures. They use either ammonium nitrate or urea and a
packet of water. Squeezing the bag breaks the packet, and the act of these salts dissolving in water is extremely endothermic. I've never heard of one
freezing from this, but you never know I suppose.
The suggestion of ammonium chloride + barium hydroxide is a great one. That's an experiment I've wanted to try for a while. It's interesting that it's
a solid/solid reaction, and it produces 10 moles of water per mole of hydroxide!
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Praxichys
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Ammonium nitrate in water will definitely get cold enough to freeze water, but not cold enough to freeze the mixture itself. This is evidenced by
frost appearing on the outside of a stainless steel container containing the mixture.
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MrHomeScientist
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Ahh that's right, excellent observation! I had forgotten that the mixture inside the cold pack would have a lower freezing point than pure water. So
while the cold pack itself might not freeze, making a setup like the OP mentioned might do the trick.
Remember that water has a high specific heat capacity, so it'll take a whlie to cool down a large amount of it.
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Praxichys
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I think the classic demonstration of this is to place a stainless steel container of the ammonium nitrate/water mixture onto a wet block of wood.
After a minute or two, the water freezes and they can be lifted in unison.
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blogfast25
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According to this resource:
http://www.chem.umn.edu/services/lecturedemo/info/Endothermi...
… the standard enthalpy of reaction for the neutralisation of solid bicar with dissolved (strong) acid is about + 28.5 kJ/mol. Assuming this value
doesn’t depend too much on temperature, to cool a slurry of NaHCO3 from 20 C to 0 C (20 K temperature difference) by neutralising it with the
required amount of HCl solution, so that the total mass of water would be 1 kg, just over 3 moles of bicar would have to be neutralised or just over
252 g of NaHCO3. This does not take into account the heat capacity of the dissolved NaCL
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gatewaycityca
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I finally got a thermometer and took some measurements. I filled a cup with vinegar, and let the thermometer sit in it for a while so that it would
adjust to the temperature. It showed 74 degrees F. Then I added baking soda. The temperature went down pretty fast...after adding a little more
baking soda and vinegar and getting another reaction or two, it ultimately dropped down to 60 degrees!  I honestly wasn't expecting that. I was <i>hoping</i> there would be a significant temperature drop, but
I expected maybe 5-10 degrees at most. I got 14! So this was a pleasant surprise!
It's a simple experiment, but I'm getting excited at the possibilities. I'm wondering what I could do with insulating the containers, using some kind
of heat exchange system, this could be pretty interesting. And just with baking soda and vinegar. I'm going to try to mix baking soda and citric
acid from some lemons next to see what happens.
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blogfast25
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In science we use Celsius or Kelvin, never Fahrenheit. All of 'heat science' is built around Kelvin.
A delta of 14 F is about 8 Celsius drop, kind of what I would expect from a simple cup type experiment.
To push the limits, vinegar isn't great because it only contains about 4 - 5 % acetic acid, which means you are cooling a lot of water, unnecessarily.
Ditto lemon juice. Using a stronger solution of HCl or H2SO4 reduces that effect.
For instance on the page I linked to, they use 3 mol/L HCl. Vinegar is only about 0.8 mol/L acetic acid. And of course it stinks too. 
For best insulation, think Dewar flask: double walled, vacuumed and silvered containers like thermos flasks.
Edit: for the experiment involving 8.4 g bicar and 33 ml of 3 M HCl, I predict a temperature drop of about 19 Celsius (assuming perfect insulation and
100 % completion of reaction though).
[Edited on 15-2-2014 by blogfast25]
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gatewaycityca
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Okay, I'll try to remember to use Celsius. I'm not used to it though, so it might take me a little while!
Blogfast25, I'm a little confused though. I did a little searching after your post, and I read that hydrochloric acid and baking soda would cause an
<i>exothermic</i> reaction. It seems that it would only result in CO2 being released and saltwater being produced, which would be safe.
(I'm trying to stay away from reactions that release hydrogen.)
Also, could I make concentrated acetic acid from vinegar? Or boiling lemon juice to concentrate citric acid? (I imagine either of them would smell
really strong, so I'd have to do that outside!) Would that get a stronger reaction by eliminating water?
Thanks for your help! I'm learning a lot from this site! 
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Oscilllator
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@gatewaycityca Concentrating vinegar an appreciable amount has been tried numerous times on this board and has been established to be extremely
difficult and often more expensive than buying glacial acetic acid. Citric acid can be bought from the supermarket, although I suppose you could
concentrate lemon juice to get some kind of impure syrup.
You are correct however that you would get a stronger reaction by eliminating water.
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blogfast25
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| Quote: Originally posted by gatewaycityca | Blogfast25, I'm a little confused though. I did a little searching after your post, and I read that hydrochloric acid and baking soda would cause an
<i>exothermic</i> reaction. It seems that it would only result in CO2 being released and saltwater being produced, which would be safe.
(I'm trying to stay away from reactions that release hydrogen.)
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No, the neutralisation reaction of bicar with ANY acid is ALWAYS endothermic. Separating the b*llcrap from the gems on the Interwebs isn't always
easy. Misinformation here [internet] rules.
HCl can be store bought as patio cleaner, here (UK) also as toilet descaler. H2SO4 (usually 95 %) as drain unblocker. Both very cheaply.
Citric acid is cheap as chips and can be dissolved to quite high strength (high solubility).
You mean by eliminating water altogether? Apart from the fact that fizzing may become so intense as to be unmanageable, in the case of glacial acetic
acid chances are your reaction would become exothermic.
Why? Because when you react solid NaHCO3 with pure GAA (chemically HOAc) you’re preparing sodium acetate in high concentration:
NaHCO3 + HOAc === >NaOAc + CO2 + H2O, that mol of water would be the only one!
If (and only if) the sodium acetate crystallises it sheds a lot of heat: it’s the operating principle of some ‘reversible chemical hand
warmers’.
[Edited on 16-2-2014 by blogfast25]
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vmelkon
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| Quote: Originally posted by Oscilllator | | @gatewaycityca Concentrating vinegar an appreciable amount has been tried numerous times on this board and has been established to be extremely
difficult and often more expensive than buying glacial acetic acid. |
I'm sure it is expensive but it isn't difficult.
1. Make sodium acetate by dumping NaHCO3 into vinegar.
2. Let it dry. Collect crystals.
3. Dump conc H2SO4 on it and heat it and collect vapors of acetic acid.
At least you avoid the cost of transportation when you order over the web which would be 30$. With 30$, I can buy 10 jugs of 4 L of 4% vinegar.
Signature ==== Is this my youtube page? https://www.youtube.com/watch?v=tA5PYtul5aU
We must attach the electrodes of knowledge to the nipples of ignorance and give a few good jolts.
Yes my evolutionary friends. We are all homos here. |
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blogfast25
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| Quote: Originally posted by vmelkon |
At least you avoid the cost of transportation when you order over the web which would be 30$. With 30$, I can buy 10 jugs of 4 L of 4% vinegar.
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http://www.ebay.co.uk/sch/i.html?_trksid=p2050601.m570.l1313...
Free postage on both 2 entries. I buy mine on eBay and pay normal rates for shipping. Totally affordable.
Yeah, good luck converting that. 40 g of HOAc per liter. Do let me know how you get on, won't you?
Not to mention the fact that you're getting the trihydrate, hardly the best starting point to obtain pure acetic acid, is it?
[Edited on 16-2-2014 by blogfast25]
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plante1999
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You gotta love Canada for shipping, it is ALWAYS minimum 15$ unless it come from china.
I never asked for this.
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Zyklon-A
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I think that sodium bicarbonate and an acid will not react unless water is present. As it is only basic in solution.
[EDIT] I'd like to test this, but I do not have any glacial acetic acid ant the moment. I do have ~98% sulfuric acid, so I just tried it with that...
It fizzed a little (likely from the 2% water), certainly not as much as even 5% acetic acid, then I added some water, and it fizzed a lot more.
This, however, does not prove much, because the extra speed of the reaction may (partially) have been because of the heat from the water addition.
[Edited on 17-2-2014 by Zyklonb]
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Turner
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When ammonium nitrate crystalizes out of solution, for example the solution cools, or too much water evaporates, is there a change in temperature?
Just as dissolving NH4NO3 cools a lot, crystalizing it should heat that equal amount?
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gatewaycityca
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| Quote: |
No, the neutralisation reaction of bicar with ANY acid is ALWAYS endothermic. Separating the b*llcrap from the gems on the Interwebs isn't always
easy. Misinformation here [internet] rules. HCl can be store bought as patio cleaner, here (UK) also as toilet descaler. H2SO4 (usually 95 %) as
drain unblocker. Both very cheaply. |
Thank you, blogfast25. That makes a lot more sense now! Is it still correct though that the reaction would only release CO2?
I can get HCl pretty easy and cheap from a swimming pool supply shop. They use acid to control the Ph in pools, and it's sold by the gallon. It's
pretty common and a lot of places sell it, even grocery stores and hardware stores. I can get a box of 2 gallons for around $8 I think. I don't know
what the concentration is, but I do know that you would normally add a very small amount to a pool to lower the Ph. And our pool is about 12,000
gallons! So it must be pretty strong stuff in the amount they sell.
I still like the idea of playing around with concentrated citric acid though.
Thanks to everyone here for helping with my questions. I'm definitely learning a lot!
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blogfast25
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Yes. Only CO2. Regardless of acid used.
Try citric acid by all means. Try and work quantitatively if possible; i.e. measure everything: weights and temps...
[Edited on 17-2-2014 by blogfast25]
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blogfast25
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| Quote: Originally posted by Turner | | When ammonium nitrate crystalizes out of solution, for example the solution cools, or too much water evaporates, is there a change in temperature?
Just as dissolving NH4NO3 cools a lot, crystalizing it should heat that equal amount? |
Yes, that's correct. But if you start from a saturated solution, you still need to put in the heat to evaporate the water to force the solute out of
solution as crystals.
But a super saturated solution of sodium acetate when it suddenly crystallises develops heat and quite a bit too.
[Edited on 17-2-2014 by blogfast25]
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