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Mixing Sodium Hydroxide and Water

Richard Rankin , Jun 16, 2002; 06:54 a.m.

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


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Julio Fernandez , Jun 16, 2002; 09:00 a.m.

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.

Christopher Hawkins , Jun 16, 2002; 10:12 a.m.

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.

Eugene Singer , Jun 16, 2002; 11:17 a.m.

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".

Esben Jensen , Jun 16, 2002; 12:10 p.m.

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.

Jon Dubovsky , Jun 16, 2002; 01:32 p.m.

The lesson we drill into all first-year chem students here when they step into the lab:
Do what you oughta,
Put the acid in the watta.

Same thing applies to bases.

David B , Jun 16, 2002; 02:23 p.m.

All the above is correct and not an over exageration. David Bickerdike Chemistry Lecturer/Teacher

Bill L , Jun 16, 2002; 02:38 p.m.

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;

Wayne Crider , Jun 16, 2002; 03:57 p.m.

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.

Dhananjay N , Jun 16, 2002; 04:09 p.m.

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

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