[tooma]

I have dissolved 213 grams of NaOH flakes (99% purity) by 425 grams of water and it completely dissolved after 4 hours (solution of 10 M of NaOH). Then I added 1118 grams of liquid Sodium Silicate (Na2SiO3) (55% water). I normally leave it for 10 hours then use the solution for my research, but this time I left it for 48 hours and found it completely different than what I used to see. a white solid balls of 1" diameter maximum size was formed. I took the attached picture after removing the liquid that covered the balls (the liquid consistency is the same as the Sodium Silicate liquid thus I supposed it is Sodium Silicate liquid). A layer of hard and solid glassy materials was formed in the bottom of the plastic pail that I left the solution in. Can anyone tell me what is that white balls and what is the glassy material that formed from this experiment.

Thanks.

[Borek]

No idea what it is, but looks quite interesting. Probably there is an interesting mechanism behind the ball formation.

If you were following a recipe that worked in the past I would assume one of the reagents used is not what you think it is (or is heavily contaminated) - and as it is this contamination (or something outside of the specification) that is responsible for the effect it can be almost everything.

[tooma]

No idea what it is, but looks quite interesting. Probably there is an interesting mechanism behind the ball formation.

If you were following a recipe that worked in the past I would assume one of the reagents used is not what you think it is (or is heavily contaminated) - and as it is this contamination (or something outside of the specification) that is responsible for the effect it can be almost everything.

Borek,

No reagents were used, but the tap water was used for dissolving the NaOH flakes. Is it possible that this is the normal results of mixing NaOH with Na2SiO3 for 48 hours? Or maybe it was caused by containments as you said .

[P]

Could some of the water have evaporated over the 2 days leaving the NaOH to solidify out? Doesn't that form little balls like this?

[tooma]

Could some of the water have evaporated over the 2 days leaving the NaOH to solidify out? Doesn't that form little balls like this?

By the end of the 48 hours I end up with three components; White balls, glassy hard and solid material at the bottom of the pail, and liquid that cover both balls and glassy material and thus very little evaporation has taken place. I believe that the glassy material is solid NaOH (it for sure didn't resulted from evaporation), Unfortunately, I did not weight the three components to have more information about them. Now, supposing that the glassy material is solid NaOH (or maybe something else), what are the white balls supposed to be?

[P]

The glassy material sounds like the silicate...  the white balls look like the NaOH and the liquid is the solution of both.

If you leave some sodium silicate solution laying around for 2 days then you would expect some evaporation and some glassy silicate to form on the surface for sure. 


S0 - imo - it doesn't look like a reaction at all, rather the solids crashing out of a saturated solution due to evaporation of some of the water.

[P]

Does it all mix back in or do you need to add some extra water to get it to redissolve?

[Borek]

No reagents were used

Well:

mixing NaOH with Na2SiO3

(yes, NaOH is there mostly to keep the pH high, but for me technically these are reagents, just like water is in this case).

What was the temperature, was the mixture covered? Such concentrated solutions don't dry easily, they often build a layer of a solid on the surface, which makes drying even slower. Doesn't mean the idea suggested by P is wrong, just the time scale (especially when comparing 48h with 10h) doesn't make it plausible for me.

[tooma]

The glassy material sounds like the silicate...  the white balls look like the NaOH and the liquid is the solution of both.

If you leave some sodium silicate solution laying around for 2 days then you would expect some evaporation and some glassy silicate to form on the surface for sure. 


S0 - imo - it doesn't look like a reaction at all, rather the solids crashing out of a saturated solution due to evaporation of some of the water.

There is one important notice that I would like to highlight, the materials shown in the picture is about 1/4 of the pail height and the liquid was covering it to 1/2 of the pail height. I spilled the liquid before taking the picture. Anyway, your answer still valid to me but need more demonstration. Do you think that the surface of the Na2SiO3 liquid which was exposed to air has gradually solidified and sank to the bottom and that this process continued until I stopped it after 48 hours and a layer of glassy silicate was formed as a result?
Is it normal that NaOH solution solidify to white balls if left for long period of time?

[tooma]

No reagents were used

Well:

mixing NaOH with Na2SiO3

(yes, NaOH is there mostly to keep the pH high, but for me technically these are reagents, just like water is in this case).

What was the temperature, was the mixture covered? Such concentrated solutions don't dry easily, they often build a layer of a solid on the surface, which makes drying even slower. Doesn't mean the idea suggested by P is wrong, just the time scale (especially when comparing 48h with 10h) doesn't make it plausible for me.

Temperature was in the range of 25-35 oC and the solution was exposed to air. You maybe right that the liquid has dried at the surface and this gives me an idea that it was sank to the bottom of the pail to form that layer on the bottom

[P]

You maybe right that the liquid has dried at the surface and this gives me an idea that it was sank to the bottom of the pail to form that layer on the bottom

This is the bit I find odd though...  if it was just drying I would expect the glassy formation to form over the surface rather than sink..   not sure. You would certainly have lost quite a bit of water if it started 35C and was left open for 2 days. That's still my best guess.

Let us know if you work out what happened! :-)

[tooma]

Does it all mix back in or do you need to add some extra water to get it to redissolve?

I added water and left it for about 2 days until the white balls disappeared. The glassy layer at the bottom lasted for five days until it completely dissolved and meantime I changed the water three times.

[Enthalpy]

Had the solution an opportunity to absorb CO₂ from the air?

[tooma]

Had the solution an opportunity to absorb CO₂ from the air?

Yes, it was exposed to the air

[P]

Does it all mix back in or do you need to add some extra water to get it to redissolve?

I added water and left it for about 2 days until the white balls disappeared. The glassy layer at the bottom lasted for five days until it completely dissolved and meantime I changed the water three times.

Sounds like it dissolved back in  -  I reckon the glassy material (silicate) would have dissolved back in quicker with excess warm water and agitation....  particularly the agitation - stirring speeds this up massively.

Just thinking aloud - I seem to remember that the solution gets pretty hot when NaOH dissolves.