Sciencemadness Discussion Board

Baking Soda in water

e.liska - 3-9-2017 at 02:49

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?

theAngryLittleBunny - 3-9-2017 at 03:00

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 ^-^

e.liska - 3-9-2017 at 03:10

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?

XeonTheMGPony - 3-9-2017 at 03:55

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!

unionised - 3-9-2017 at 06:22

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.

e.liska - 3-9-2017 at 09:30

So is there any critical temperature of the solution that should not be reached to keep the bicarbonate? Will the pH change?

ninhydric1 - 3-9-2017 at 10:51

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]

e.liska - 4-9-2017 at 20:29

Is there some easy way to distinguish between baking and washing soda when I get my dry crystalls?

JJay - 4-9-2017 at 22:32

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.