When I dissolve KOH pellets in water I observe bubbles coming from the solution. Is it H2 or water vapor?
It all depends on the purity of the youor KOH (solid powder). For example, if your KOH is 100% pure hydroxide, then when mixed with water it ionizes to give potassium ions (K+) and (OH-) ions. Water also ionizes into (OH-) and (H+) ions.
If, however, your KOH powder contains elemental potassium, then it will react with H2O to produce H2 gas and KOH (in ionic form).
Hope this helps answer your question.
Professor Yehia Khalil, Yale University, USA
Fellow of the University of Oxford, United Kingdom
Probably you have a bit of carbon dioxide combined with the KOH. Also it could be air bubbles if the water starts highly aerated. Probably it is not hydrogen or water vapor.
Pellets are normally porous and the air in the pores will be released as bubbles while KOH dissolves.
I suggest they are air bubbles. The solubility of air is less in hot water and KOH pellets heat up the water locally as they dissolve exothermically.
Prof Khalil: I have never heard of KOH containing free potassium. This could be very dangerous, and as one of the Editors of Bretherick's Handbook of Reactive Chemical Hazards, I would appreciate you giving the literature source.
Prof. Pitt - In my chemical engineering teaching lab, we keep alkali metal pellets like sodium and potassium in an inert environment (N2 gas). Only when the pellets are dropped in water, a vigorous exothermic reaction occurs and H2 gas is released. I assumed that the KOH pellets were not 100% pure hydroxide salt and kept under an inert environment before coming in contact with water.
Prof Khalil: as I understand it, the principal impurities are water (increasing with time if a jar is repeatedly opened and small portions taken out), sodium hydroxide and potassium carbonate. I see no reason why potassium metal should be there, but would be glad to be told otherwise if this actually occurs.
KOH pellets or flakes are normally supplied in plastic jars or sacks. It is not susceptible to oxidation like Na or K so does not need to be kept under nitrogen, but should be guarded from moisture as it is deliquescent.
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