What is "chlorine"? Lets talk ions and stuff.

[spinjector]

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!

 

[Analog Saint]

Chlorine is just what you think- dissolved diatomic chlorine gas. It doesn't stay in solution very long, and that's why Chloramines are sometimes used. And yes, that chlorine gas is the same stuff that was used on WW1 battlefields. There's a push to move to Ozone because of two major reasons 1) Ozone can be made on-site and doesn't require transportation of a very poisonous gas under pressure 2) Ozonolysis (use of ozone and reducing agent) is quite effective as an antimicrobial. Oh, and Chlorine can react with things in the presence of heat or UV light to form highly reactive chlorine radicals, which are a whole world of bad news.

Chloride test kits- haven't seen em, but chloride is the Cl(-) ion, so one could safely assume that's what it tests. Dunno what good it would do you.

Equilibria and Solubility... Just thinking about that is giving me flashbacks of G-Chem 2. Although, I'll give that class some credit, I actually do use Chem 2 know-how when dealing with my tank.

 

[YoFishboy]

Here are a couple of sites that discuss chlorine, chloramine and all kinds of chemicals in our tap water that affects our tanks - http://www.advancedaquarist.com/issues/jan2004/chem.htm and http://www.aquahobby.com/articles/e_parameters.php - maybe these sites are a good place to start this discussion.

 

[Raskolnikov]

What is the "chlorine" compound used in tapwater..?

When I called the head chemist at my water treatment plant for information on my tapwater (boy, was that a runaround), he said that they used Sodium hypochlorite. You may recognize this as common household bleach.

"It produces an unpleasant working environment for workers because it has poor stability in water which results in gassing off---being released into air."

http://www.btcproducts.co.za/clo2_compare.asp


.

 

[Kasakato]

So it smells?

 

[happychem]

Yes, in areas where a lot of chlorine is used the tap water can have a distinct bleach smell. Often this just has to do with your proximity to the treatment plant and the distance between the treatment plant and the farthest customer. Since chlorine dissipates with time (read distance) the farther the water needs to travel, the more chlorine is added. This is why chloramines are often used, chloramines do not evaporate like chlorine does so there's not a need to use as much.

As Raskolnikov found out, the chlorine added to pools and water treatment is sodium hypochlorite (NaOCl), which in water dissociates to Na(+) and OCl(-) - hypochlorite. Hypochlorite can react with a chloride ion (Cl-) and H+ to form water and Cl2. There is no transport of pressurized Cl2.

Ozonolysis is one alternative mainly derived from a desire to move away from chlorine based water treatment. The problem with ozone is that it's expensive to produce and it's toxic and generally not something that you want to be producing en-masse. In the stratosphere, O3 is a good thing, it protects us from UV; in the upper troposphere, it's a good thing since it photolyses (by absorbing UV) to (ultimately) produce OH radicals which convert CO (carbon monoxide) to CO2 and CH4 (methane, about 15 times worse a greenhouse gas as CO2) to CO2 and again. In the lower troposphere it's not a good thing, it's toxic to those of us who breathe O2 and is carcinogenic - causes cancer - by dissociating into O2 and an oxygen radical.

In short, there's no real advantage to O3 over Cl2. Both are toxic (or they wouldn't do the job) and both evaporate. The biggest motivator is scare tactics that attempt to convince people that Cl2 is bad, they usually reference things like it being a chemical warfare agent in WWI and the inherent dangers of Cl2, all very true. However, Cl2 is not used in the chlorination of tap water and the amounts that are actually present are tiny. Quite a number of years ago there was a successful lobby in one of the SA countries (Brazil, I think, but I'm not positive) to stop chlorinating water because of the evils of chlorine, it was associated with an outbreak in typhoid fever, so they started chlorinating again, goodbye typhoid.

I've never heard of a chloride test kit, it's not easy to test for, being very unreactive.

Chlorine - Cl2
"chlorine" - I think is what you're calling NaOCl (or even just -OCl), but for all intents and purposes, Cl2.
chloride - Cl-
prefixes:
hypo- : one oxygen atom less than min (eg. hypochlorite: OCl)
per- : one oxygen more than max (eg. perchlorate: ClO4)
suffixes:
-ite : the minimum stable valence (eg. chlorite: ClO2)
-ate : the maximum stable valence (eg. chlorate: ClO3)

I think that I got most of everything in there, probably missed or messed up something though...

 

[Stefanie]

yes, you can smell it if your nose is not desensified over time...
Actually after I just moved to the us from a country where there is never chlorine in the water, for the first few month i felt like being in a swimming pool when taking a shower... now i do not smell it anymore... only in ice cubes in my soda.