Why is adding water to chlorine more dangerous than adding chlorine to water?

[_N3WTON_]

So, unfortunately a neighbor of mine had a terrible accident involving pool chemicals. He added water to chlorine and started shaking it, causing an explosion that left him in bad shape (luckily, I am told he will make a full recovery). I have not had a course in chemistry in a few years (although I still know enough to realize what he did was quite foolish), so I am wondering, how is the chemistry different between adding chlorine to water vs adding water to chlorine? If somebody could give me an explanation I'd greatly appreciate it, thanks.

 

[leafjerky]

"The reaction of an isocyanurate (Dichlor, trichlor) with hypochlorite (calcium hypochlorite) can result in rapid formation of nitrogen trichloride, which at high enough concentrations will detonate spontaneously with great violence."

REFERENCE: http://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=73

 

[_N3WTON_]

"The reaction of an isocyanurate (Dichlor, trichlor) with hypochlorite (calcium hypochlorite) can result in rapid formation of nitrogen trichloride, which at high enough concentrations will detonate spontaneously with great violence."

REFERENCE: http://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=73

I appreciate the response but mainly what I'm wondering is why is it OK to add chlorine to water but not vice versa?

 

[Borek]

I'm wondering is why is it OK to add chlorine to water but not vice versa?

In general when diluting (or reacting) something concentrated it is better to add it to excess water. That helps quickly dissipate reaction products and heat, reducing risks.

 

[_N3WTON_]

Awesome, thanks!

 

[Emmanuel_Euler]

So, unfortunately a neighbor of mine had a terrible accident involving pool chemicals. He added water to chlorine and started shaking it, causing an explosion that left him in bad shape (luckily, I am told he will make a full recovery). I have not had a course in chemistry in a few years (although I still know enough to realize what he did was quite foolish), so I am wondering, how is the chemistry different between adding chlorine to water vs adding water to chlorine? If somebody could give me an explanation I'd greatly appreciate it, thanks.

Did You mean Cl2 gas ??

 

[mp3car]

Most likely he did not mean chlorine gas, as I think it would be hard to "add water to gas" since chlorine gas for pools is stored compressed in cylinders.

However, I am still not following why adding water to a chlorine solution (presumably water and calcium hypochlorite), or hypochlorite powder would cause a reaction, unless there was something in the water... the sentence preceding the quote that @leafjerky posted is as follows: "Finally, if the choice is to alternate between stabilized and unstabilized chorine, they should not be stored near each other. The reaction of an isocyanurate with hypochlorite can result in rapid formation of nitrogen trichloride, which at high enough concentrations will detonate spontaneously with great violence."

This doesn't sound what the OP's neighbor did, as this would involve mixing two chemicals. HOWEVER, where did the water come from? It seems like, unless the water he was adding to the chlorine had something disolved in the water of fairly high concentration (an isocyanurate?), I'm still not following how adding "tap water" to a liquid chlorine solution (if pool places still sell those yellow jugs), or water to a powder, would cause a violent reaction...

I DO know strong chlorine is dangerous/reactive stuff, and can be "fun" to play with for a pyromaniac 16 year old... (Back when you could be a 16 year old pyromaniac and set a pipe bomb off in the woods and not be guilty of committing a terroristic act and locked up for 10 years...)

 

[mp3car]

Correction to my post above... if it were a liquid form, I think it would be sodium hypochlorite and water, not calcium hypochlorite.

 

[James Pelezo]

One of the essential safety mandates that chem students learn early on in basic chem courses is ... when preparing solutions of strong acids such as Hydrochloric Acid (HCl) from commercial stocks, one should always add the pre-determined amount of concentrate (cautiously) to at least a 2.0x larger volume of water, then dilute to the desired solution volume. NEVER EVER add a larger volume of water into a small quantity of concentrated acid. The rate of ionization will be so fast that the heat generated would explode the mixture and cause serious injury. Remember A&W Root Beer... Acid into Water - NEVER - Water into Acid. The same is true for mixing hypochlorite salts. Adding the salt into the water instead of water into salt moderates the ionization/reaction rate and minimizes the potential for explosion. I always hate to hear of someone hurt b/c of misapplication of chemical reagents. Remenber, if you are not familiar with application of a chemical (and that includes anything easily purchased locally) please read the instructions and, of course, follow them. It always takes less time to do a job right the 1st time than to pay the price (health or dollars) of doing it over. Hope this helps.

 

[mp3car]

That's perhaps the problem... I am an EE, and the only reason I recall ever learning about adding acid to water from a saftey reason was because of "splashing" :(

 

[James Pelezo]

That's perhaps the problem... I am an EE, and the only reason I recall ever learning about adding acid to water from a saftey reason was because of "splashing" :(

Well, at least you've has some exposure to how to handle this type system. I just wish it were promoted more widely. Good job.

 

[Borek]

when preparing solutions of strong acids such as Hydrochloric Acid (HCl) from commercial stocks, one should always add the pre-determined amount of concentrate (cautiously) to at least a 20x larger volume of water

Always at least 20x larger volume? So how do you prepare 3 M solution of HCl if that calls for approx 1:3 dilution?

 

[James Pelezo]

Always at least 20x larger volume? So how do you prepare 3 M solution of HCl if that calls for approx 1:3 dilution?

Assume needing 100-ml of 4M HCl(aq), [HCl]_conc = 12.1M (common concentration of commercial stock HCl(37%)
(Vol Conc)(M Conc) = (Vol Dilute)(M Dilute) => Vol Conc Needed = [(Vol Dilute)(M Dilute)]/[M Conc]
Vol Conc Needed (ml) = (100-ml Soln)(4M HCl) / (12.1M HCl)
= 33.05-ml Conc HCl

To a 150-ml Griffin Beaker containing ~ 70-ml of solvent (water) slowly add 33.05-ml of stock concentrate. Transfer to a calibrated 100-ml volumetric flask, then dilute up to but not to but not to exceed 100-ml. (Note: should have been, 2.0x vol of conc. not 20x... Left out decimal. my bad.