Close, Bill, but no cigar. [:)] Dissolution is not the same thing as corrosivity. Sugar and salt dissolve in water, but even though water is the universal solvent, it is not considered corrosive. A corrosive, by definition, is any material that has the potential for causing the destruction of (or irreversible damage to) living tissue at the site of contact. For a material to be corrosive, it must have a pH of less than 2 (acidic) or a pH greater than 12.5 (basic). Many folks consider strong acids to be the only corrosives, but even dilute solutions of potassium, sodium, or even ammonium hydroxide (strong bases) can be quite corrosive. There are, of course, other bases as well.
You are correct about oxidation. That is typically the effect a chemical material has on a metal. Water is a great oxidizer…
Gip is giving you the definition of “corrosion” from the viewpoint of the effect a material has on the human body.
From the viewpoint of the inorganic chemist, there is no precise definition, because the process is poorly understood, and often involves very different systems. For example, the corrosion of metal is generally thought of as oxidation—except that oxygen does not have to be involved, nor are the chemical reactions necessarily those classified as reduction/oxidation reactions. In silicate chemistry, the situation is even more complex and confusing.
And I’d like to add that, terrible as acid burns may be, alkali burns are far worse. My former employer often testified in cement (portland cement is highly alkaline) burn cases, and I was involved in some of them. The pictures are not for the weak of constitution.
One of the things that makes alkali solutions so dangerous is that usually, by the time you realize that you have a problem, it is much too late. By the time they start to hurt, you are already severely “burned.”
I’m using corrosive as meaning the ability to eat away or be erosive, as opposed to the definition of corrosive meaning destructive. Acetone does not work on oil and grease the same way water does on salt and sugar.
Many people assume only the latter definition applies to corrosive. I did not mean corrosive such as an acid would have. Prolonged exposure to acetone does have the ability to cause dermatitis.
As I understand it, alkali solutions have the unique ability to destroy nervous tissue (as well as skin, muscle and fatty tissue), and therefore cause substantially “painless” tissue destruction, while acids are known to physically burn the skin as they “eat” their way through. Correct me here, but I believe portland cement contains calcium hydroxide, a very powerful base. I used to insist our laborers wear rubber boots and gloves (and eye protection, too) when pouring concrete.
My understanding is that alkali solutions penetrate all tissue relatively rapidly, compromising everything they encounter—nerves are dead before they can send signals. It is only when the adjacent tissue reacts that pain is felt. The only acid that does this is hydrofluoric, and I believe the molecular mechanism is similar, IIRC.
Portland cement, when combined with water, produces enormous amounts of calcium hydroxide (mineral name: portlandite) and also produces substantial amounts of the alkali cations (mostly sodium, some potassium). The pH of normal plastic portland cement (the binder in concrete) is 13.8 and higher. Actual effective pH of wet concrete exceeds 14.
So don’t stop insisting on rubber boots, gloves, knee pads, and eye protection! And at the end of the day, work clothes go into the laundry, they are not worn again until they are washed. Any article of absorptive clothing that comes in contact with plastic (wet) concrete or cement is immediately removed, no exceptions and no exclusions! (Making a construction worker remove his pants in public just once is usually enough to convince everyone…) I recall once a foreman literally cut the pants off a worker, who had refused to take them off (he’d fallen into the concrete that had just been placed.) The worker was dumbfounded, then furious. I stopped him cold when I showed him a picture of a cement burn. He went from furious to tossing his cookies. (Such a picture was part of my field kit—ruined some lunches, but stopped arguements.)
Acetone is “lipophilic”—it dissolves lipids, or fat-like substances. That is why it causes dermatitis.
“Corrosive” is generally chemical. “Erosive” is physical, as in breaking a part off. (Of course, on the molecular scale, the distinction blurs…[(-D]
Actually, the effect acetone has on lipids is analogous to that of water on sugar and salt, in an organic chemistry sort of way. Some lipids return to their original state after solution in acetone and evaporation, similar to the purely ionic solution and redeposition of salt and sugar in water. However, the analogy breaks down with other lipids, which are chemically altered by exposure to acetone.
Technically, your use of “corrosive” may not be correct, but in a literary sense, the meaning is clear. [swg]