Is "anhydrous potassium hydroxide" (dry KOH) the same as "potassium oxide" (K2O)?

Question

I know K2O + H2O --> 2KOH

So if you just add water to K2O to get KOH, then wouldn't dehydrated KOH be the same thing?  You have to add water to it to get a caustic reaction as well.

? · Accepted Answer

NO
when you add water to K2O a chemical change takes place.  Exactly One H2O molecule combines with each K2O molecule to give 2 KOH molecules.

KOH IS anhydrous - its a white powder, or sometimes supplied as pellets with a varying (small) amount of water in the mix. However its very hygroscopic and if left exposed to air will rapidly go tacky and eventually dissolve in the absorbed water.

KOH forms a series of crystalline hydrates, namely the monohydrate KOH·H2O, the dihydrate KOH·2H2O, and the tetrahydrate KOH·4H2O.

You can dry it out by heating it when the absorbed water will evaporate off.  However it will be KOH that you get.

If heated it will melt but still not return to K2O.

Is "anhydrous potassium hydroxide" (dry KOH) the same as "potassium oxide" (K2O)?

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