So real chlorine
is an element. And it happens to be a gas. Most of you have never
seen or smelled the pure stuff, and those of you who have wish you
hadn't. Chlorine is so dangerous it has books written and courses
given on just its safe handling. And chlorine's always hungry to
become a compound, as you'll see.
The most common
compound formed by chlorine in water is hydrochloric acid, HCl.
(l, not 1.) That's hydrogen and chlorine in compound. This common
and powerful acid is formed when water, even moisture, gives up
some of its hydrogen (H) to chlorine (Cl) when the two get together.
It is, incidentally,
this hydrochloric acid that makes chlorine so poisonous. It forms
HCl when contacting the moisture in the lungs, doing great damage
to the little parts (alveoli) in there. HCl also is the reason chlorine
is considered so corrosive. That's the acid formed by chlorine,
not chlorine itself, which corrodes. (Pure, elemental chlorine is
shipped in steel bottles yet they don't corrode... There's no water
in the tanks to produce the corrosive acid.)
Does any of
this help us in pools? Yes, indirectly – and mostly in the
understanding of general water-chemistry principles. We're not yet
finished with what happens when chlorine mixes with water...
Specifically,
the mixture of chlorine and water gives us one more compound that
is the one we really want. It is hypochlorous acid.
Sounds pretty much like hydrochloric acid. It's not. This one is
very mild as acids go, yet a very good worker as you'll
see. Here's a formula – the only one we'll ever give you,
promise. "Read my lips...
Hypochlorous Acid (Spoken Hi-po-chlor-us asid): Oh m'gosh, another big chemical term. Well, this is the most important stuff you'll ever study in the water-chemistry curriculum.
Hypochlorous acid is the compound of chlorine which does all the disinfecting and oxidizing that most of us will ever need in our pools. This is the good guy – the chemical we want in the pool to the exclusion of all others (if we could be so lucky). This one is worth memorizing; you'll sound like you really know your chemistry!
Trouble is, hypochlorous acid isn't very stable – it doesn't hang around long. If it did, it probably wouldn't work very well, so we put up with its fragile nature, constantly adding more chlorine, playing with the pH, adding other magical chemicals and chewing our nails off trying to keep HOCl around and working. That's what Chapter 10 in the AFO manual is all about.
A few last words about chlorine. Most of you know that there are many other forms of chlorine at the pool supply store, and surmise by now that they're compounds, not the element itself. True. Sodium hypochlorite is liquid "chlorine bleach". Calcium hypochlorite is "dry" or "granular" chlorine. And there are more. They all produce that fleeting and wonderful HOCl, hypochlorous acid, when mixed with water, and that's what we want!
There are pH effects resulting from the addition of each type of chlorine. Obviously gaseous (elemental) chlorine, which makes a powerful acid (HCl) as a by-product, will drive the pool water in the acid direction – or to lower pH numbers. The two chlorine compounds mentioned above drive the pH upward, not downward, indicating that the good-guy hypochlorous acid (HOCl) isn't much of an acid; other factors are much stronger in the pH-upward direction when using either bleach or calcium hypochlorite.
In the course you'll find out not only that chemicals have an effect on a pool's pH, but the pH of the water has a significant effect on how well the chlorine works! The lower the pH, the more powerful the chlorine. As pH rises near 8 or higher, on the other hand, the chlorine becomes very weak.
This pH business as it relates to chlorine is very important. It will be covered in Chapter 10 and thoroughly in the course; don't worry about it right now.
Prep School Basics :: Other Stuff |
