e.liska
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Baking Soda in water
I am sorry if my question is stupid but I am just a beginner.
I experiment with baking soda. When I add it to cold water, it dissolves peacefully. If I add it to hot water, it bubbles a lot and releases carbon
dioxide.
But what happens when I dry the resulting solution? Will I get the baking soda again, or because CO2 was lost in the hot water, I get something else
(washing soda or NaOH, I do not know)? And from cold water, do I get my baking soda back or is it the same as with hot water, just slower, so I do not
see the bubbles?
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theAngryLittleBunny
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Baking soda is sodium bicarbonate NaHCO3, when you heat it, it loses CO2 and forms sodium carbonate Na2CO3
2NaHCO3 -> Na2CO3 + CO2 + H2O
So what you're left with in the solution is sodium carbonate, and if you boil down the sodium bicarbonate solution, it will also decompose and you
will get sodium carbonate.
And don't worry about your question sounding stupid, everyone here was a beginner once ^-^
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e.liska
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So if no high temperatures are involved (no heating, drying slowly), would I get back the bicarbonate?
And what about the Na2CO3? Doesn't it also lose some CO2 to produce NaOH?
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XeonTheMGPony
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No you end up with Carbonate all the same, but it will slowly take CO2 from the air to become bicarbonate if I recall. But it will not become
hydroxide to make a hydroxide takes considerable energy!
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unionised
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If my memory serves me right, the version which is stable in air is the sesquicarbonate.
If you let a solution of either bicarbonate or carbonate evaporate slowly you will mainly get back what you started with, but some of it will be
converted to the sesquicarbonate.
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e.liska
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So is there any critical temperature of the solution that should not be reached to keep the bicarbonate? Will the pH change?
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ninhydric1
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According to Wikipedia, above 50 degrees Celsius does the decomposition take place slowly. Above 200 degrees Celsius, the reaction occurs much more
rapidly.
If you want to regenerate your sodium bicarbonate from sodium carbonate solution, build a carbon dioxide generator (usually acetic acid (vinegar) and
sodium bicarbonate) and bubble the carbon dioxide through the room temperature sodium carbonate solution. You may see precipitation due bicarbonate's
lower solubility than carbonate, which is fine. If you bubble carbon dioxide through the solution for long enough, almost all of the sodium carbonate
will be converted back to sodium bicarbonate. If you want to recover the sodium bicarbonate in solid form, chill the starting sodium carbonate
solution (but don't let any of it precipitate out), bubble the CO2, and collect the bicarbonate precipitate that crashes out.
EDIT:
Let me include the equation:
Decomposition reaction:
2 NaHCO3 --> Na2CO3 + H2O + CO2
The opposite reaction is the regeneration of sodium bicarbonate.
One more thing: sodium bicarbonate is safe to consume but sodium carbonate is NOT. That's why it's important to bubble an excess of carbon dioxide if
you plan to use this solution for consumption.
[Edited on 9-3-2017 by ninhydric1]
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e.liska
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Is there some easy way to distinguish between baking and washing soda when I get my dry crystalls?
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JJay
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I don't think that crystalline forms of sodium carbonate absorb carbon dioxide to a significant degree. Dissolving carbon dioxide in a saturated
solution of sodium carbonate causes sodium bicarbonate to precipitate due to its lower solubility. This is exploited commercially on a massive scale
to produce sodium bicarbonate. Neither sodium carbonate nor sodium bicarbonate are substances that you want to eat with a spoon, but both are safe to
consume in low concentration. Sodium carbonate is sufficiently caustic to cause burns at high concentration, but generally this requires extended
contact (but don't get it in your eyes). It can be tricky to tell them apart, but sodium carbonate is more soluble and neutralizes more acid per unit
weight. Also, it forms hydrates. More carbon dioxide per unit weight is given off when neutralizing sodium bicarbonate.
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