Sciencemadness Discussion Board

How do I make a sodium hydroxide solution from caustic soda?

dobeid - 8-11-2008 at 10:03

Hi:
I need to mix up a strong lye solution to bring an acidic mixture to a pH of 14. I have the caustic soda (NAOH) but am confused as to how much distilled water to add to how many grams of caustic soda to create the strong lye solution that I need.

If anyone can educate me on this I would be most appreciative.

Thanks

[Edited on 8-11-2008 by dobeid]

crazyboy - 8-11-2008 at 12:14

NaOH+H2O=>sodium hydroxide soloution.

Caustic soda is sodium hydroxide which is NaOH. Just add sodium hydroxide to water until it is at the correct pH.

Thanks Crazyboy.

dobeid - 8-11-2008 at 12:21

chief - 8-11-2008 at 14:33

Watch out: I gets hot, sometimes beyond boiling point, and may spit around the hot and dangerous (at least to the eyes) NaOH-solution ! Wear protective glasses, or don't do it !!!!

Nerro - 8-11-2008 at 14:46

pH 14 = pOH 0 which means you need 1M NaOH in water. -log(1) = 0, conversely 10<sup>-0</sup> = 1/10<sup>0</sup> = 1/1 = 1 :)

And, always add acids and bases to water, never the other way around, that way theres not so much acid/base splashing about.

Jor - 8-11-2008 at 15:13

I have seen an eye splashed with NaOH solution. You DON't want that........

Klute - 8-11-2008 at 16:53

The proper procedure would be to gradually add NaOH pellets to a very well stirred, cooled volume of distilled water.
Do not be afraid of taking your time, even 20min, NaOH pellets liberate large amounts of heat when they dissolve, and there can be a latency, as it takes a little moment to heat up, and then as more dissolves, the heating increases, often to over 100°C!

So do it slowly, and with very good stirring!

smuv - 9-11-2008 at 12:29

I like to prepare sodium hydroxide solutions in plastic cups, as sodium hydroxide has a tendency to fuse itself to the bottom of Pyrex glassware.

Just a little tip.

Picric-A - 9-11-2008 at 12:35

I used to remove lightly fused NaOH form glassware by covering the fused mass with water and slowly adding conc HCl..
I have heard a dilute soloution (around 5%) works wonders for cleaning fused solids off glassware.... never tried it myself though.

Nerro - 9-11-2008 at 13:07

To be honest when I'm in a lab I usually just dump the pellets in water and let it stir for a while. As long as it's in a fumehood and off to the side nothing is really going to happen. Obviously you should ALWAYS wear glasses and keep your head out of the fumehood.

So long as you THINK about what you're doing you'll be fine.

smuv - 9-11-2008 at 13:33

Quote:
I used to remove lightly fused NaOH form glassware by covering the fused mass with water and slowly adding conc HCl..


In my experience there is still a blemish left on the glassware even after washing with acid, because the spot where the pellet gets fused gets etched. Best to avoid the problem altogether and use plastic...

[Edited on 11-9-2008 by smuv]

chemrox - 9-11-2008 at 17:50

Quote:
Originally posted by Jor
I have seen an eye splashed with NaOH solution. You DON't want that........


what happened? In general bases are much worse than acids on eyes and skin

Jor - 9-11-2008 at 18:06

Yes I know it's very late :D Can't sleep!

I didn't see it in real life, but on a picture. Our lab assitent wanted to show us to show us how dangerous chems can be.

Well the eye was gone, it had turned into a slurry. Just red flesh was left, like a hole. It was a mess. According to one of the professors, getiign a base like NaOH conc. in the eye will mean almost certain blindness, while with acids there is still hope.

crazyboy - 9-11-2008 at 20:59

Quote:
Originally posted by Klute
The proper procedure would be to gradually add NaOH pellets to a very well stirred, cooled volume of distilled water.
Do not be afraid of taking your time, even 20min, NaOH pellets liberate large amounts of heat when they dissolve, and there can be a latency, as it takes a little moment to heat up, and then as more dissolves, the heating increases, often to over 100°C!

So do it slowly, and with very good stirring!


How big are your pellets? It seems like people are talking abut chunks of NaOH about the 1 cm long correct? Strange I have only found it very small prills.

MagicJigPipe - 10-11-2008 at 00:06

My experiences with NaOH differ slightly. Whenever I add water to NaOH pellets (just enough to dissolve them completely) it gets hot but hardly ever heats up over 60*C. Why is that?

Also, there is never any splashing/boiling.

And the boiling point of NaOH solution is greater than 100*C (and much more if it is saturated).

[Edited on 11-10-2008 by MagicJigPipe]

UnintentionalChaos - 10-11-2008 at 00:18

MagicJigPipe- Try splashing a little water onto a pile of prills and there will be quite a bit of nasty steam coming out of the vessel. I have a HDPE jar with a liquid tight lid that I shake the prills in while they dissolve so Im not stirring a huge lump at the bottom of a container but I need to open it repeatedly to relieve pressure and afterwards, it is sometimes too hot to touch.

crazyboy- Standard lab grade stuff is usually half-oval shaped pellets between 3/4 and 1 cm long. The drain cleaner stuff is almost universally flakes or tiny round pellets.

Klute - 11-11-2008 at 22:21

Well, no they are quite small pellets (0.5 cm wide, 0.2cm high), and pouring water directly on them causes a hell of a mess, often fusing to the bottom of the glass immediatly...

The solution itself doesn't boil indeed, but gets superheated at some points, where it ca,n sizzle and splash everywhere... and you have to wait 10min in a ice bath to get it to room temp anyway, so might just aswell take 10min to prepare the solution, which will be ready and a room temp, with much less carbonaet formation IMHO.

Directly adding water to NaOH (or conc acid BTW) is a very dangerous thing to do. I do not see any advantage to it either.

Foss_Jeane - 22-11-2008 at 14:25

Quote:
Originally posted by MagicJigPipe
My experiences with NaOH differ slightly. Whenever I add water to NaOH pellets (just enough to dissolve them completely) it gets hot but hardly ever heats up over 60*C. Why is that?


Because you've been damned lucky so far. I wouldn't push it.

Why do you think "Red Devil Lye" makes such a good drain opener? As soon as the pellets hit the water in the goose neck, it gets very hot -- hot enough to melt the grease and other gunk that got stuck down there. Even then, gitdahellawayfromdere! It can boil over and come shooting back up the drain.

I always add the NaOH or KOH flakes/prills to cold water with the beaker sitting in an ice water bath. So it takes time to prepare concentrated solutions. What's better: waiting 20 mintes for your solution, or living the next 50 years blind as a bat?

P.S. Since we're on the subject, NH4OH safety: chill the bottle before you open it. That way, you cut down the pressure so it won't shoot out a nasty cloud of ammonia. Allow to warm up to room temp with the cap cracked so that you don't have an increase of air pressure as it warms. That sort of defeats the purpose. Of course, you wouldn't be using this stuff unless you had a fume cubboard, right?

Need I say goggles, goggles, goggles?

[Edited on 22-11-2008 by Foss_Jeane]