Chemistry geek question

[TexEdmond]

It's been a long time since I had the privilege of taking a chemistry class. But I know that one cannot create or destroy matter, so here's my question:

SWCGs use electricity to dissociate salt water into useable chlorine (I suspect it ends up as sodium hypochlorite) and hydrogen gas, which stays out of solution and bubbles off into the atmosphere.

Theoretically, if I'm ending up with something that's effectively stealing the O from water and glomming onto NaClO while throwing away the H2, wouldn't that theoretically mean that the SWCG is a kind of thunderdome situation? Two water molecules enter, one leaves? Or that's to say, for every molecule of NaClO that's produced, one water molecule is lost and I'll need to refill my pool extremely slightly more often than normal evaporation and splash-out? Or maybe more accurately, I'll have to replace 1 molecule of water for every molecule of hydrogen gas that bubbles out? I know these are likely very small numbers.

Somebody geek me out on stoichiometry. My chemical engineer brother is coming back thru town in a week and I want to talk smart to him over a drink.

 

[zea3]

Paging @JoyfulNoise

 

[mknauss]

There was a recent very long winded thread on this subject. I am looking for it.

Salt water generators are closed systems... what?

So I was watching this nice information packed video on SWCGs... And JoyfulNoise sort of mentioned off-hand that pool store workers "don't understand that the chlorine cycle in salt water generators is a closed system" and this is why you don't have to keep adding salt. To which I told my...

www.troublefreepool.com

 

[JamesW]

for every molecule of NaClO that's produced, one water molecule is lost and I'll need to refill my pool extremely slightly more often than normal evaporation and splash-out? Or maybe more accurately, I'll have to replace 1 molecule of water for every molecule of hydrogen gas that bubbles out? I know these are likely very small numbers.

You are basically correct.

For every 1 lb of chlorine gas produced, you lose about 0.2538 lb of water (about 3.89 fluid ounces).

H2 (hydrogen gas) is produced in the cell and the hydrogen gas bubbles out into the air.

For hypochlorite (OCl^-), the chlorine steals two electrons from the oxygen to create oxygen gas.

2OCl^- --> 2Cl^- + O₂

 

[TexEdmond]

There was a recent very long winded thread on this subject. I am looking for it.

Now that you mention it I definitely visited that thread. Must not have read all the way thru, or the water loss question wasn't addressed when I was there last.

 

[TexEdmond]

For every 1 lb of chlorine gas produced, you lose about 0.2538 lb of water (about 3.89 fluid ounces).

Gotcha. So if my SCG makes 2lbs max per day, the loss is a little less than a cup of water. Pretty negligible indeed.

Also not worth rigging up some kind of hydrogen capture tank...