Problems when mixing sodium carbonate

[Gungo]

Hello,

I’ve put 594g of sodium bicarbonate in the oven for 1 hour to make sodium carbonate but I’m trying to mix it and after a few hours the solution does not clear up. It has a brown-yellow color and I’m not able to see the bottom of the 1 gallon jug.

Any reason? Is this normal?

 

[lapin]

Perhaps you over cooked it. Did it burn?

 

[Gungo]

I thought about it. When I took it out of the oven there was some smoke but the powder was white.

 

[lapin]

I duno. Maybe someone has some ideas.

 

[redfishbluefish]

I'm going to speculate that it was "under cooked," leaving it as sodium bicarbonate. I say that for two reasons. One is that you'd need very high temperature to decompose sodium carbonate. The second reason is that it's not dissolving and sodium bicarbonate is roughly half the solubility of sodium carbonate.

Temperature needs to be over 176F (80C) for the carbon dioxide to be blown off. I usually cook at 350F for an hour. (I think Randy's recipe says 300F). The other consideration is how thick was the baking soda in the oven. I spread it out on a cookie sheet so it's maybe 1/4 inch thick or so. IF it's too thick I could see it now getting hot enough in the center of the mix.

 

[redfishbluefish]

Here's a test. Put some of the mixture in a coffee cup and microwave to a boil. The decomposition of sodium bicarbonate will still occur in solution as long as you exceed 176F. If the solution is now clear, that's what your problem was....didn't fully decompose the sodium bicarbonate to the carbonate form.

 

[Randy Holmes-Farley Verified Community Expert]

Do you see undissolved white solids, or just discoloration?

It certainly is not overcooked. Even in a blast furnace it will remain something white that is water soluble (calcium oxide).

Underbaking can impact the ultimate solubility, but not normally the color.

What was the origin of the sodium bicarbonate? Maybe it just wasn't pure enough.

 

[Gungo]

Here's a test. Put some of the mixture in a coffee cup and microwave to a boil. The decomposition of sodium bicarbonate will still occur in solution as long as you exceed 176F. If the solution is now clear, that's what your problem was....didn't fully decompose the sodium bicarbonate to the carbonate form.

I tried this and it didn't clear up. I ended up throwing it away.

Do you see undissolved white solids, or just discoloration?

It certainly is not overcooked. Even in a blast furnace it will remain something white that is water soluble (calcium oxide).

Underbaking can impact the ultimate solubility, but not normally the color.

What was the origin of the sodium bicarbonate? Maybe it just wasn't pure enough.

There were some undissolved white solids and discoloration. Please see a picture here. The source of the bicarbonate is a local shop that sells pharma-grade stuff, I even buy calcium and magnesium from them and never had a problem before.

 

[Gungo]

Just tried to prepare a new mix with the same batch of sodium carbonate to see if it was a problem with the powder and I noticed that the last time I used a wooden spoon to stir and mix. This time I used a metal spoon just in case and it cleared up pretty quickly. Maybe what happened here is that I used the wooden spoon and the carbonate and water discolored the spoon leaving the residue in the mix.

Thanks to all for the input.

 

[atoll]

The small difference in cost between buying sodium bicarbonate carbonate doesn't make it worth while making your own IME

 

[Randy Holmes-Farley Verified Community Expert]

The small difference in cost between buying sodium bicarbonate carbonate doesn't make it worth while making your own IME

Do you have a cheap source of quality sodium carbonate?

 

[atoll]

Do you have a cheap source of quality sodium carbonate?

BlueBay Aquatics 1KG - Sodium Carbonate Anhydrous Granular TATA Soda Ash pH Dye 99.7% Na2CO3 https://amzn.eu/d/hSV98C2

That's about $8 for a kilogram.

 

[Randy Holmes-Farley Verified Community Expert]

BlueBay Aquatics 1KG - Sodium Carbonate Anhydrous Granular TATA Soda Ash pH Dye 99.7% Na2CO3 https://amzn.eu/d/hSV98C2

That's about $8 for a kilogram.

You can get sodium bicarbonate with a better purity guarantee for less. That's the reason I proposed baking baking soda.

 

[atoll]

You can get sodium bicarbonate with a better purity guarantee for less. That's the reason I proposed baking baking soda.

I never suggested it was cheaper only that the difference was minimal with not having to heat it in the oven which adds to the cost of making your own. 99.7% purity of the sodium carbonate is fine plus I don't get any scum etc. What purity is the sodium bicarbonate you advise?

 

[Randy Holmes-Farley Verified Community Expert]

I never suggested it was cheaper only that the difference was minimal with not having to heat it in the oven which adds to the cost of making your own. 99.7% purity of the sodium carbonate is fine plus I don't get any scum etc. What purity is the sodium bicarbonate you advise?

Food grade. Spec is 99-100.5%. Aside from the % purity, the remainder of which could be anything, it has a heavy metals limit (lead less than 2 ppm). It also has a "no ammonia odor" spec.

 

[atoll]

Food grade. Spec is 99-100.5%. Aside from the % purity, the remainder of which could be anything, it has a heavy metals limit (lead less than 2 ppm). It also has a "no ammonia odor" spec.

Thanks, I can't smell anything from my sodium carbonate plus surly if there is ammonia in it the amount I dose (1 heaped teaspoon in my ATU water, 10ltr every 2 days) would be insignificant. As for lead I will try and find out what the 0.03% impurities are.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks, I can't smell anything from my sodium carbonate plus surly if there is ammonia in it the amount I dose (1 heaped teaspoon in my ATU water, 10ltr every 2 days) would be insignificant. As for lead I will try and find out what the 0.03% impurities are.

It has likely fine at that high percent purity.

 

[Gungo]

I baked another 594 grams of sodium bicarbonate at 180c for 1 hour and it mixed pretty quickly but my question is, I'm confused with the color of the water on the soda ash/sodium carbonate. I mixed 1 gallon of sodium bicarbonate from the same source and the water is 100% transparent but the water on the soda ash looks a little different. Could this be due to added concentration of sodium bicarbonate? I just want to confirm if this is normal or if I am doing something wrong.

 

[Randy Holmes-Farley Verified Community Expert]

Slight discoloration of dosing solutions is not generally a concern. Typically it will come from trace elements such as iron, and a little color may mean very little trace element. Baking can oxidize trace elements to different forms that may have more or less light absorption or solubility.

I presume the soda ash one is twice as concentrated, as per the recipe?

 

[Gungo]

Yeah, soda ash = sodium carbonate meaning is twice the concentration. I was concerned.