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What gas is released during dissolving solid $\ce{NaOH}$ in a high purity water? Water more than 10 M$\Omega$/cm and standard quality $\ce{NaOH}$.

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  • $\begingroup$ If the water had some dissolved ammonium ions in it, those could evaporate when you raised the pH by adding NaOH ($\ce{NH4+ (aq) + OH- (aq) -> NH3 (g) + H2O}$). But that seems unlikely, and in any case, the smell would be very distinctive. I can't really think of any other obvious candidates for volatile cations one might find in water. $\endgroup$ – Ilmari Karonen Mar 12 '15 at 19:10
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I don't think any gas is released. You are probably experiencing dust or mist that contains NaOH itself, or tiny amounts of gas phase NaOH.

There is related discussion at a soapmaking website

http://www.tikvah.com/medical/lye.html

See also "Pneumothorax following inhalation of caustic soda fumes" Archives of Emergency Medicine, 1988, 5, 45-47

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  • $\begingroup$ I will check it next time. $\endgroup$ – Jaroslav Kotowski Mar 12 '15 at 16:49
  • $\begingroup$ @JaroslavKotowski You might be able to detect NaOH in the air from a bunsen burner flame turning yellow above the open vessel. $\endgroup$ – DavePhD Mar 12 '15 at 17:15
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That is simply air included in the evaporation/drying process.

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  • $\begingroup$ The gas is not possible to breath, it maks me cough. And its temerature is same as ambient. $\endgroup$ – Jaroslav Kotowski Mar 12 '15 at 16:09
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    $\begingroup$ I agree the gas is likely air. Breathing it is a horrible idea though, because it it likely to contain aerosolized sodium hydroxide, which could reach your lungs and do some damage. Be safe! $\endgroup$ – Curt F. Mar 12 '15 at 16:41
  • $\begingroup$ Thx for the answer, try to avoid it if you prepare 100 l of 5% solution in an open tank. $\endgroup$ – Jaroslav Kotowski Mar 12 '15 at 16:46
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I think it is due to the heat of solvation of NaOH, causing the solution to evaporate. If you dissolve NaOH with a large amount of solution, the "gas" wouldn't be released.

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Thanks for the comments. Based on them, here what I observed: The thank is filled with 100 l of water then $\ce{NaOH}$ is added. If it is added slowly, no bubbles or gases were observed. We need to shorten the preparation time so we stirred it intensively. During stirring, air bubbles are introduced to the solution. After their release, a alkaline mist/water dispersion is released to air - that is what I was observed. Thanks again for your thoughts.

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Ammonia is possible in the small amount.

$$\ce{NH4+ (aq) + H2O (l) <=> NH3 (aq) + H3O+ (aq)}$$

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    $\begingroup$ This answer is in no way different than the comment by Ilmari Karonen to the original question. Also, Welcome to Chemistry.SE. Take the tour to get familiar with this site. Mathematical expressions and equations can be formatted using $\LaTeX$. $\endgroup$ – Martin - マーチン Mar 13 '15 at 7:56

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