Re: How do acids burn or dissolve matter?

The answer to why acids burn, dissolve matter and eat through paper and 
metal is a complicated one.  Even the topic of strong acids versus weak 
acids also gets into the picture.  I'd like to start there.  All acids 
produce hydrogen ions in water solution.  Strong acids are those that are 
especially good at that.  Weak acids are poor at doing this.  When a weak 
acid dissolves in water, only a small portion of it forms hydrogen ions.  
It is the hydrogen ion that reacts with some metals to "eat" through 
them.  The hydrogen ions react with the metals and are converted to 
hydrogen gas.  The metals are converted to soluble metal ions.  Strong 
acids do this more effectively (faster) than weak acids.

In the case of paper, the acid (hydrogen ions) reacts with the cellulose 
(the wood fibers from which the paper is made)to cause a decomposition (a 
breaking into smaller pieces).  As the fibers break into smaller pieces, 
they become detached from one another and are further degraded by the 
acid.  Most of the reason why paper yellows and weakens as it grows old is 
from some very small amount of residual acid left in the paper from the 
process by which it is made.

The "burning" of skin is similar to the paper situation, but more 
complicated yet, because of the variety of materials present in the skin 
and flesh.  One part of that picture is that the hydrogen ions react with 
the peptides (proteins) and other components of the flesh to cause a 
decomposition.  Again it is a breaking apart of these materials into 
smaller pieces.  Not good for the skin.

On the other hand, the fluid in our stomachs, the gastric juices are very 
acidic, because the strong acid aids in the decomposition of the food so 
that we can make use of the pieces from the food items.  The stomach 
lining is special; it is not attacked by the acid, unless the acid level 
is too high for too long, and then the acid breaks through the lining to 
form an ulcer.

I hope that this helps; mail me if you have more questions.

Dr. Jerry Franzen
franzenj@thomasmore,edu