Trouble with Caustic Soda

[veron]

Hi,

I have been reducing the amount of water for sodium hydroxide. I use a little more water in the 1: 1 ratio, but I have had the problem that it is not completely transparent as when I use more water.

When I add just a little bit of water the mixture becomes more cloudy and it is difficult to get it back to the initial state and the heat does not help much either. In fact, when the temperature drops it becomes a little more transparent.

My question, can I use this slightly cloudy solution to saponify the oils? I imagine that the sodium hydroxide will be consumed and increase the solubility for the little bit that seems to be in suspension.

I would also like to know if to make a 50% sodium hydroxide solution you have to leave it for an hour or a day to dissolve completely, I have not found an exact protocol on how to do it.

Pls, help

I have been using demineralized water and sodium hydroxide pellets (98 %).

 

[ResolvableOwl]

Sounds like you have minor contamination with sodium carbonate: the NaOH pulled CO₂ from the air.
Sodium carbonate (soda ash) is freely soluble in water, but insoluble in concentrated NaOH solution, so it won't dissolve, but give a bit of sediment. When a container with lye solution stands open, this will happen by itself, when a thin crystalline crust forms, floating on top of the lye.

There is little you can do to revert this. Where ultimate precision is paramount (chemistry, pharmacy), they use freshly distilled water in the first place (over time, distilled/demineralised water will pull some CO₂ from the air as well), and then decant/filtrate off the insoluble carbonate.
However, it sounds that your contamination isn't that bad to make such drastic (and laborious and wasteful and dangerous) measures necessary, on a soapmaker's level.
When the carbonate forms (but also with pulling water from the air), the lye gets slightly diluted, i. e. your purity drops a bit. In soap, this leads to slight increase in superfat.

When in doubt and possible, only use freshly opened containers of NaOH and distilled water/use up a whole batch at once, to minimise air contact.

I would also like to know if to make a 50% sodium hydroxide solution you have to leave it for an hour or a day to dissolve completely, I have not found an exact protocol on how to do it.

Quite some of the folks around here do routinely make lye masterbatch. I have no experience with this, but that concentration is definitely doable (someone else to chime in!).
Regular stirring/shaking will be helpful (but try to minimise air contact, soda ash danger!), a magnetic stirrer would be ideal.

 

[TheGecko]

I'm by no means as expert when it comes to Sodium Hydroxide, but I do know that if you add more water to the cooled solution, that it will heat up and become cloudy again.

Prior to master batching my Lye Solution (where I make up a couple of gallons of 33%-35%), I would either make individual containers and let them sit in the garage overnight, or make them in the morning for use in the afternoon. But I have also use the Heat Transfer method, where you use a freshly made Lye Solution that is 200F+ to melt your hard oils without issue.

 

[veron]

Thank you for your answers. My concern was that the case of undissolved sodium hydroxide could damage the skin later or that NaOH was not consumed in the saponification. I imagine that sodium carbonate does not have a major impact on the formula. In any case, I will take the care that you recommend, because I left the beaker uncovered.

 

[earlene]

You can pour your MasterBatched or cloudy lye solution through a sieve into the weighing vessel prior to adding it to your oils.

If you thoroughly mix the water with the dry NaOH prior to letting it cool and the solution does not get too cold, it should not come out of solution if you mixed it with the total weight of 1:1 mix. There will be some evaporation while it heats up, so add back in the few grams of water (for me it's about 4 to 6 grams of water lost to evaporation during the mixing).

I always shake up my MasterBatched lye solution prior to weighing out the required amount. My bottles have tight child-proof lids, which I make sure are quite tight & keep my gloved fingers on the lid while shaking. If it appears to be cloudy, I use a sieve just to be safe. On rare occasions I have had NaOH come out of solution and leave a little crystalline disk at the bottom of the container (in the deep winter when my house gets really cold.) That disk doesn't just fall apart & end up in the measuring vessel, but if I hear the disk inside my MB bottle, I know that the solution is not 1:1 when I pour it through the sieve and I know I'll have a higher superfat than planned.

 

[veron]

I used a glass beaker and after adding the NaOH I quickly covered the glass with aluminum foil.
No precipitate formed in the solution (or floating precipitate). Before, precipitate formed on the walls as well (the remaining water that splashes on the walls of the glass when mixing with a rod).
There was only a slight cloudiness which must be from the sodium carbonate of the water, because I did not use fresh water (I have demineralized water from a while ago).
Later I will do it in a stainless steel or plastic jug of 5.
I was thinking of using Parafilm but I don't know if the steam eats it or just keep using the aluminum foil.
I bought a polypropylene bottle with a screw cap, so I'll leave it slightly open at first and then close it to keep out air.

 

[DeeAnna]

Oh, dear -- Please, PLEASE don't use aluminum around NaOH or soap batter. Aluminum reacts with sodium hydroxide to release flammable hydrogen gas and corrosive sodium aluminate.

If you want to cover your sodium hydroxide solution with something -- and that's something I've recommended many times -- then use a plastic cover, waxed paper, a paper towel, or a cloth rag. Even plastic food wrap. Any of these options is better than foil.

 

[veron]

Ok, thanks