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Old 15th March 2019, 07:57 PM   #1
Skeptic Ginger
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Chemistry question re bicarb

Thanks in advance.

I put baking soda (sodium bicarb) in a glass of water. It tastes salty.

In the morning it has a soap-like taste.

And later in the day a precipitate forms.

Can any of you tell be what the slow chemical changes are with baking soda and water?

Thanks
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Old 15th March 2019, 11:35 PM   #2
BowlOfRed
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Originally Posted by Skeptic Ginger View Post
I put baking soda (sodium bicarb) in a glass of water. It tastes salty.
That's the sodium part. I'm a bit surprised that's the first thing you get. Could be direct ionization:
NaHCO3 + H2O -> H2CO3 + (OH-) + (Na+)

Quote:
In the morning it has a soap-like taste.
Sodium carbonate is "washing powder".
2(NaHCO3) -> Na2CO3 + CO2 + H2O

Even though this reaction produces water, it doesn't happen (much) when dry, but does when it's wet. (I don't know why) So that would be the soapy taste.

It can further break down as
Na2CO3 -> Na2O + CO2

But apparently the sodium oxide is not stable in water. So whatever is precipitating out is something else.

Sodium carbonate is used as a water softener, precipitating out other minerals. I wouldn't expect that to be enough to be visible, but if it doesn't form in distilled water, that could be the reason.
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Old 16th March 2019, 01:52 AM   #3
EHocking
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If it is Baking Powder, rather than bicarbonate of soda, the precipitate is most likely from the Cream of Tartar added to the bicarbonate.

What are the other additives listed?
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Old 16th March 2019, 02:41 AM   #4
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Very hard water and the bicarb is saturating the water, causing Ca or Mg carbonate to precipitate out? (Yep, my chemistry was mostly forgotten decades ago )
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Old 16th March 2019, 07:07 AM   #5
pgwenthold
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Originally Posted by GlennB View Post
Very hard water and the bicarb is saturating the water, causing Ca or Mg carbonate to precipitate out? (Yep, my chemistry was mostly forgotten decades ago )
That was going to be my suggestion. You've got calcium salts forming.

I don't know anything about the soapy taste, but that would explain the precipitate.
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Old 16th March 2019, 11:29 AM   #6
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Sodium BI- carbonate degenerates to sodium CARBONATE, also known as Washing Soda.

You can do it yourself on purpose by heating baking soda to ummm 250f? Taste before and after- or taste some powdered dish washer soap, it is mostly washing soda. Much more caustic, you don't want it on your hands. But it cleans greasy clothes very well, same for greasy dishes. Now I use Cascade in the laundry.
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Old 16th March 2019, 11:40 AM   #7
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Originally Posted by BowlOfRed View Post
That's the sodium part. I'm a bit surprised that's the first thing you get. Could be direct ionization:
NaHCO3 + H2O -> H2CO3 + (OH-) + (Na+)



Sodium carbonate is "washing powder".
2(NaHCO3) -> Na2CO3 + CO2 + H2O

Even though this reaction produces water, it doesn't happen (much) when dry, but does when it's wet. (I don't know why) So that would be the soapy taste.

Would the NaOH not explain the soapyness?
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Old 16th March 2019, 11:51 AM   #8
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Chlorine? And what else is in your water?
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Old 18th March 2019, 12:05 AM   #9
Skeptic Ginger
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Originally Posted by EHocking View Post
If it is Baking Powder, rather than bicarbonate of soda, the precipitate is most likely from the Cream of Tartar added to the bicarbonate.

What are the other additives listed?
It's soda, not powder. I'll look for other ingredients in the morning, though. I hadn't thought of that.
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Old 18th March 2019, 12:07 AM   #10
Skeptic Ginger
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Originally Posted by Trebuchet View Post
Chlorine? And what else is in your water?
That's right, there is some chlorine in the water, hopefully not much else.

Originally Posted by BowlOfRed View Post
...

Sodium carbonate is used as a water softener, precipitating out other minerals. I wouldn't expect that to be enough to be visible, but if it doesn't form in distilled water, that could be the reason.
I will try distilled water tomorrow.

I knew you guys would know, thanks.
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Last edited by Skeptic Ginger; 18th March 2019 at 12:09 AM.
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Old 18th March 2019, 07:24 AM   #11
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Originally Posted by Skeptic Ginger View Post
Thanks in advance.

I put baking soda (sodium bicarb) in a glass of water. It tastes salty.

In the morning it has a soap-like taste.

And later in the day a precipitate forms.

Can any of you tell be what the slow chemical changes are with baking soda and water?

Thanks
If you are using bi-carb to fight acid reflux, get modern. H-1 inhibitors are much better for you.

Or to soak dental appliances in overnight? Okay, that is why you are familiar with taste changes. hmmmm. I doubt you want to complicate things with a neutralizing bath of vinegar water in the AM? Or use carbonated water for the overnight soak? Metal parts don't like acid baths.
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Old 19th March 2019, 12:02 PM   #12
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Originally Posted by GlennB View Post
Very hard water and the bicarb is saturating the water, causing Ca or Mg carbonate to precipitate out? (Yep, my chemistry was mostly forgotten decades ago )
That would be my guess, but Mg would probably be precipitating as MgOH, as that has very low solubility.

As others have suggested, the sopy taste after it has sit overnight is probably because it has offgassed CO2 and some of the bicarbonate has become carbonate, raising the pH.
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