1.12.13-8. KOH and NaOH are highly hygroscopic, meaning that they avidly attract and hold water vapors from the atmosphere. Both absorb so much moisture from the air that eventually they can dissolve in the water absorbed (watch this video
). The process by which a hygroscopic substance self-dissolves in the water it has absorbed from the atmosphere is called deliquescence
. The absorption of water vapors from the air commences on the surface of a hygroscopic material. The larger the surface area, the faster the rate of the moisture uptake will be. A powdered solid substance always has a larger surface area than a pellet or block made of the same quantity of the same substance. It is for this reason that pellets of KOH and NaOH are less hygroscopic and more convenient to work with than KOH and NaOH powders.