How does chlorine evaporation work??!?!?

If the chlorine is already bound to another molecule in the tap water and has become inert then we wouldn't really need to worry about it, right? That's also not technically chlorine anymore, it's another molecule all together.

There is still some free chlorine in tap water though I believe. If there isn't then that means your water may not be getting sufficiently disinfected because any free chlorine should bond with something so if there's no free chlorine then that means that there is potentially something in the water that hasn't been bound with chlorine.
http://www.cdc.gov/safewater/publications_pages/chlorineresidual.pdf

Chlorine itself boils at a rather low temperature, below freezing, so boiling the water is not necessary to remove free chlorine from water.
WikiAnswers - What is Chlorine's boiling point and melting point

To me that seems to mean that it is the free chlorine evaporating that we're smelling from the tap. Ultimately it sounds to me like the chlorine does both, it binds to a bunch of things and becomes relatively inert and it also evaporates.

 

I agree....


To pdgoodsell....I think the sunlight/warmth speeds up the bonding process. In your pool, the chlorine bonds to all of the crap in your pool like sweat, blood and tears. The hotter, the more people swimming and sweating. So the more going on, the more the chlorine is slowly used up.

 

That's a great question, and one I asked GoToSleep a few days ago. I just began to use filter socks, and I've been doing a lot of reading about their care and cleaning. Seems many people wash them in the laundry with just a cup of bleach and nothing else. Also seems most folks slip in an extra rinse cycle as insurance to get rid of the bleach. In fact, many people simply refuse to use bleach because "they're nervous."

For more than 20 years, I've used bleach on live rock dozens of times, then rinsed with freshwater and allowed to dry. My nose has always suggested that the bleach is gone after drying is complete.

Back to the point, chemistry isn't my forte, and since MDs have to take (at the very least) chemistry, and organic chemistry, I asked GoToSleep if the extra rinse cycle was necessary. I assumed a normal laundry cycle followed by a 3-day air dry would be more than enough to neutralize any traces of bleach.

Here's his answer, I quote:

"The short answer is I think that you are absoloutely right and your proposed method is perfectly safe.

For the long answer-- Chlorine is a diatomic (2 atom) molecule composed of 2 atoms of Cl- The bond between these two atoms is pretty weak and when they break apart they are very reactive and potent oxidizers (another potent oxidizer in some tanks is ozone). If you let these filter socks dry the chlorine should break down and you'll just be left with some chloride ions which your tank is already filled with because salt is of course sodium chloride (NaCl). There are lots of other chloride salts in our tanks as well -- magnesium Cl, calcium Cl, etc...

The funny thing is that most of the folks getting excited about running an extra rinse cycle are probably running municipal water supplies that are, you guessed it, chlorinated. . . . "

He goes on, but there you have it. I'm confident that this would translate to rock as well (without the washing machine!!) The pertinent point being that air drying must take place to make the object safe. The nose knows.


I hope GTS doesn't mind me quoting his words, but I thought since it benefits the community, I'd post it. As a colleague of mine is wont to say, "I'd rather beg for forgiveness than ask for permission."

 

Wow....that is very reassuring and makes perfect sense. Thanks reefsparky!

 

the photons from light do produce enough energy to carry out a hydrogenation reaction with chlorine... in your pool the chlorine is being hydrogenated with the free water molecules around it, so yes, sunlight does speed up the reaction

 

I think one of the points of this thread (since it sparked from a conversation OP and I were having) is this:

let's say you use tap water for your tank. if you fill a bucket with tap water and let it sit for 24 hours (most likely in your house) - will the chlorine evaporate out of that. That is, are dechlorinators necessary if you let your water sit first?

I'm thinking that's a big no based on what i've read in this thread....

 

the chorine will take the thermodynamic path and evaporate into cl2 gas. 24 hours should be enough time to get all the chlorine to evaporate given enough surface area

 

what's enough surface area? I think for most folks we're talking about a bucket. Deeper than it is wide.

If I fill a 3 or 5 gallon bucket up with tap, is the chlorine gone 24 hours later? If so, why don't we recommend that instead of recommending de-chlorinators as a rule on 3reef?

 

I wouldn't recommend de-chlorinators, how about RO/DI? ;D

Joking, but really de-chlorinators are conveniences, time-savers. I believe they're relatively cheap ($8 of prime will treat 2500 gallons) so it's not necessarily a bad recommendation if you're OK with using tap water. Maybe there should be some fine print in the recommendation that there are alternatives.

Also a good solution to the bucket problem (taller than wide with little surface area) is water circulation using and airstone or powerhead.

 

I do use RO/DI... but I used to use tap... so I'm curious. I used to fill 3 gallon bucket, add dechlorinator, let it sit for a day and then use it as top off water. Never had any problems, but seems like I was doing one more step than necessary...

For me, had I known, I would rather not use the dechlorinator and just let it sit out. Doesn't the dechlorinator cause it to not evaporate out? Since it bonds to it, doesn't it just become dissolved junk in the water? Making the "air out" method superior?


Still wondering too how long a non aerated or circulating 3 or 5 gallon bucket would need to sit to allow time for chlorine to evaporate. Bc I think that's the most common scenario (for tap users) - I mean using a bucket and no circulation for top offs.

I want to know A. for my own knowledge and B. so I can make good recommendations to people.

I'm sure there's a formula for this... not sure how to find it though... my calculator (and it's even "scientific" doesn't have a chlorine button ;D)