What is "chlorine"? Lets talk ions and stuff. - The Planted Tank Forum
 
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post #1 of 3 (permalink) Old 04-14-2005, 04:59 AM Thread Starter
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What is "chlorine"? Lets talk ions and stuff.

What is the "chlorine" compound used in tapwater..? And what is "chloramine"..? How do they both do what they do?

I ask this after seeing a "Chloride Test Kit", and it made me start thinking about a few things:

- "chlorine" and "chloride" are not the same thing

- "chlorine" as used in tapwater and swimming pools probably is not elemental chlorine, as it would evaporate. so i figure its probably some kind of multi-pronged molecule that likes to play harbour-mine and breaks up into different smaller nasty bits when it comes in contact with something that sets off its fuse

- a "chloride test kit" is probably for chlorine ions like sodium chloride amd potassium chloride.

- since putting salt in water does not make bleach, it would seem free CL ions do not make "chlorine". nor does it go boom when the sodium ions hit the water like metallic sodium would. so seems to me chlorine and "chlorine" are not the same thing.

- maybe "chlorine" releases di-atomic chlorine gas (CL2) in the water and that's what does it? perhaps like O2 or the nastier ozone O3...? What happens to the rest of the molecule? what by-products are left behind?

Perhaps a good discussion and/or review of ions and "dissociation" is in order. And of course this would apply to not just chlorine, but all the other ionic "-ite" and "-ate" compunds and such that we have in our tanks.

I know my vocabulary would make it sound like I should now these things, but I am just remembering random patches of topics from the fourm, science shows on tv, and high school chemistry class.....ummm...17 years ago...

I could Google it, but that would be like asking how butter works in chocolate chip cookies and trying to Google "butter"... See my point...? I was hoping for some directly aquarium-related discussion of these topics.

Thanks!
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post #2 of 3 (permalink) Old 04-14-2005, 11:43 AM
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Actually, clorine does evaporate from tapwater when exposed to air. That's why some of the older literature recommends *aged* water for water changes.

Unfortunately, it's not stable and as has been discovered, when free chlorine is added to water, it combines with a vast assortments of minerals, some of which are really bad for you. Chloramine is a combination of chlorine and ammonia which causes fish keepers grief because not only does it have chlorine to burn the gills, it then releases a whole bunch of ammonia to finish them off.

My mind is aglow with trancient nodes of thought, careening through a cosmic vapor of invention - Hedley Lamar
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post #3 of 3 (permalink) Old 04-14-2005, 12:52 PM
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As I understand it, much of the chlorine in the water supply is in the form of hypochlorite ion OCl-(same as bleach) at less than 1ppm (bleach is about 5%!). Some of it is also elemental chlorine (Cl2) and does off-gas. It is extremely effective at killing microorganisms in the water (E. coli, etc), but it is not extremely long-lived in the water distribution system (the water may become re-contaminated before reaching your house).

So, chloramines are often used now. Though not as great at killing microorganisms as chlorine, they stay in the water a lot longer so they end up more effective. They are also at about 1ppm in the water supply. They are made by adding ammonia to chlorine-treated water, leading to a number of chloramine products. The primary bacteria-killer is monochlroamine (NH2Cl). Since it is not ionic, it is best removed using activated carbon or treatment with hydroxymethanesulfonate (Amquel, HOCH2SO3-) which can break the chlorine-ammonia bond and bind the ammonia (activated carbon releases the ammonia).

Your chloride test kit measures Cl- (the ion), not Cl2 (the element). Chloride ion concentration is not very important in a planted tank (unless it gets really high).

Chlorine does combine with some metals to help remove them from water (iron and manganese), but these are not harmful. The harmful product is the reaction of chlorine with organic molecules to produce things like chloroform (the level of chloroform is on most water quality reports for this reason). If the people at the treatment plant are doing things right, very little chloroform is formed - of course, when things go wrong (like during heavy rains), it is worse.

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