Mixing Sodium Hydroxide and Water

In The Darkroom Cookbook, it suggests putting sodium hydroxide in a

plastic or glass container and slowly adding cold water to it, with

ice on hand, etc. In the Film Prociessing Cookbook, the same author

says always add the sodium hydroxide to cold water, and NEVER THE

OTHER WAY AROUND (his emphasis). <BR><BR>

Can someone tell me which is correct? When a neophyte,

inconsistencies like this tend to mnake one nervous....<BR><BR>

TIA and cheers,

Richard

Richard: The film processing cookbook is right. When you add water to Sodium Hydroxide a considerable amount of heat is released which can cause the mixture to splatter, shatter the container, etc., Considering that this is an extremely corrosive material specially to the eyes, the consequences can be serious. In a chemical lab, NaOH is handled with extreme care, goggles and gloves being mandatory. If neither of your books mention this, the error of omission is unforgivable and irresponsible. Even fairly dilute solutions of NaOH can cause loss of an eye even in short exposures BEWARE! It is good practice besides to always add powder to liquid to avoid lumps.

Stay safe, you were smart in asking.

Julio is exactly correct. One additional comment... If you get sodium hydroxide in your eyes, you must flood them with water for 15 minutes while holding your eyelids away. Not 5 minutes, not 10 minutes, not 14 minutes. 15 minutes. This will be hard to do, but you must. The reason is that NaOH hydrolyzes and dissolves the eye tissue. After washing with for a brief time, your eyes might feel OK but they are not. The caustic material is still in your eye and doing damage. I had a friend in graduate school who got with ammonium hydroxide in his eyes and washed them for a �few� minutes, until they stopped hurting. After a while the started to burn again and by then, he had damaged his eyes to the point that he has unable to function normally for 2 weeks. His eyes finally fully recovered, but it was a valuable lesson to everyone in the department. Regards, Chris Hawkins, Ph.D. chemist.

Richard, my copies of "The Film Developing Cook Book" and "The Darkroom Cookbook", by Steve Anchell, both contain several warnings about always adding acids and caustic soda to cold water. Never the other way around. Also, both say "always use eye protection whenever working with these types of chemicals". There is also a discussion in the Appendix III section of the film cookbook warning the reader to avoid these types of chemicals. For example," Rodinal should be obtained from Agfa in the premixed form".

Dissolving NaOH in water produces large amounts of heat. You should therefore slowly add the NaOH to the water. The water will be able to absorb the heat better if the water/NaOH ratio is great and you'll avoid accidents.

 

Same thing with concentrated acids. NEVER add water to acid.

<p>The lesson we drill into all first-year chem students here when they step into the lab:<br>

Do what you oughta,<br>

Put the acid in the watta.</p>

<p>Same thing applies to bases.</p>

All the above is correct and not an over exageration.

David Bickerdike

Chemistry Lecturer/Teacher

I know this is getting off subject a bit.... but I notice that in all natural bars of soap, they are made with an oil such as palm or coconut oil, and sodium hydroxide? The product seems so caustic from the above, why do you think it would be used in these all natural soaps? From a soap making page...

 

The common alkalis used in soapmaking are

sodium hydroxide (NaOH), also called

caustic soda;

In the air conditioning trade we use sodium hydroxide (in a solution of other ingredients) to acid clean evaporator coils. I usually add it to the water. At the strength we use it, it will take skin off your hands.

Bill, I'm trying to recollect some high school chemistry here - so I hope someone will chime in if I get any of this wrong. Soap is essentially sodium stearate. So, sodium hydroxide is used in the process of 'making' the soaps i.e., as an ingredient (its called lye in the trade). It is combined with a fat and they turn into soap through a process called saponification. At the end of the process, you actually do not want any sodium hydroxide in the soap i.e., the pH is supposed to migrate towards 7. Cheers, DJ

I cannot believe that you chemists, especially the Ph.D. variety, have answered the way you have.

 

Ponder for a moment, if you will, which has the higher boililng point: pure water or a high concentration NaOH solution?

 

Consider which has the higher heat capacity: pure water, or a concentrated NaOH solution?

 

Ponder on the question of where all that heat originates: in the dilution of concentrated solution only or from the dilution of any conentration of NaOH.

 

Now go back and give the correct answer.

Thanks for the answers. I suspected that the Film Processing Cookbook was correct as it was written later than the Darkroom Cookbook. <BR><BR> However, my copy of the Darkroom Cookbook (2nd Ed, 2000) clearly states that the easiest method is water into sodium hydroxide and suggests a method for doing so.<BR><BR> Errors like that make you wonder what ELSE might be wrong in the book....<BR><BR>Cheers,

Richard

Bruce: Adding water to NaOH will not generate explosive splatters or shatter glass, but it does get hot enough to vaporize a small percentage of the water. Have you forgotten about steam distillation? You can prove to youself that adding water to solid NaOH is a bad idea. Here is one way. Put 100g of NaOH in a 1L beaker. Add 500g water. Wait a couple of minutes, then look closely into the vessel and tell us what you experience.

Richard, you never mentioned why you were mixing the sodium hydroxide. There are only a few developer formulas that use NaOH for an accelerator. Rodinal is the most common one, and it is best to use the Agfa preparation. Sodium hydroxide is used for cleaning a clogged drain in the bathroom sink (Drano).

I agree with everyone who has said add acids and bases to water. Wear eye protection. Because dissolving NaOH generates a fair amount of heat, you may want to be careful you don't melt or weaken the container. NaOH is best stored in a plastic bottle because it can etch glass. It's not as big of a problem with a screw cap jar, but it's really annoying to see someone fuse two expensive ground glass surfaces with NaOH.

 

About soapmaking and saponification.

 

Fats are typically esterified to glycerol or a similar molecule, unless they are free fatty acids. The base hydrolyzes the ester, in essence separating the glycerol from the fatty acid. The cation (Na+) is this case and the fatty acid form a soap (sodium stearate) in this example. Put a little oil on a tube. Add some NaOH solution. Shake. You'll see soap bubbles. This is also why bases feel slippery. Some cations form insoluble compounds rather than soaps which we see as soap scum.

 

Lake Crescent in Olympic National Park is caustic enough to saponify fats. Many years ago, a man killed his wife (Hallie Illingsworth) and threw her body into the lake. She stayed submerged for several years until she saponified (turned to soap) at which time she came bobbing up to the surface. She was identified and her husband convicted.

 

 

http://www.gorp.com/gorp/features/halloween/turnsoap.htm

Eugene,<BR><BR>

I buy my Rodinal premixed. The sodium hydroxide question was in relation to mixing the Thiourea Toner from Photographers Formulary (who also say add water to the sodium hydroxide in their instructions!).<BR><BR>Richard

Can any one contribute why the heat is evolved ?

 

What makes to contribute in this regard?

Ramachandra,

As heat is required to break chemical bonds, the reverse is true so that heat is released when chemical bonds are formed.These form very quickly when a hydrogen ion from water meets an OH- ion from sodium hydroxide. Bruce,I pondered for a while about the heat capacity of water and then remembered that water is famous for having a high heat capacity. Therefore when heat is generated from the new chemical bond of water with hydroxide, the water does not boil until it has reached its full capacity of heat.Dilute sodium hydroxide presumably has a lower heat capacity and will boil and splutter dangerously when water is added to it - making adding sodium hydroxide to water the favoured option. Careful with those lumps mind you!