Adding Dry Ice to Pool

[chem geek]

I bought around 20 pounds of Dry Ice (frozen carbon dioxide) for our Halloween party and wasn't very attentive at feeding the cauldron of water with dry ice to make bubbling and fog (condensed water vapor from the cold carbon dioxide gas). It looked great each time I dumped a chunk of dry ice into the warm water cauldron (a pot with a hot plate under it to keep the water warm), but my lack of attention meant that I had around 8 pounds of Dry Ice left over when the party ended. So I did what anyone with a pool might do...

I dumped the 8 pounds of Dry Ice into the warm pool (around 86 degrees). It bubbled a lot and produced a fog over the area where I dumped it. I figured that it would lower the pH of the pool, but didn't know how much carbon dioxide would dissolve into the pool vs. get bubbled out. It looked like it was mostly bubbling out, but I wouldn't know for sure until the next day...

So now it's the day after the fun experiment and I measured the pH of the pool and sure enough, it's lower by around 0.5 (from 7.5-7.6 to 7.0-7.1). My calculations show that around 1/4th of the carbon dioxide from the dry ice dissolved into the pool to cause the pH to drop. My plan is to just keep my pool open and exposed to air to slowly outgas the CO2. If I had something to aerate my pool more effectively, I'd use it, but I don't. If the pH doesn't move, I'll add some base to get the pH up.

Better living through chemistry!

Richard

[sevver]

LOL, gotta love it. You guys are truly chemistry nutz.

[CarlD]

Richard!!!!

OY!!!

[chem geek]

Yes, it was fun, but oh so educational...

If anyone wants to do this for Halloween, you could probably get by with 5 pounds of dry ice dropping in chunks when trick-or-treaters arrive. However, if you have lots of guests continually over many hours you'll need at least 10 pounds or more. You must use gloves (leather gloves work great) when handling dry ice as it is very cold and will freeze your skin if you touch it for more than a few seconds eventually leading to frostbite -- not as bad as liquid nitrogen, but not something to fool around with. See this website for lots of great info on dry ice.

Be sure to use a heavy old pan/pot -- thick metal, but not aluminum as the acidity of the water (from the dissolved CO2) might ruin the pan. If you don't want to use a hot plate, then just change the water when it gets cool and refill with hot water (hot tap water is plenty hot enough -- even warm water is OK).

I was actually (briefly) concerned that I was contributing significantly to greenhouse gasses by using dry ice so I did some calculations. Since the body exhales about 200 ml of CO2 every minute, this is about 0.36 grams per minute or about a pound per day. So using 20 pounds of dry ice is equivalent to having 20 people breath for a day. One gallon of gasoline produces around 20 pounds of carbon dioxide so using 20 pounds of dry ice is equivalent to using a gallon of gasoline or driving 20-40 miles depending on your MPG. There, now I've made you feel appropriately guilty, so have some fun and plant a tree (one tree absorbs around 1400 pounds of CO2 over its lifetime, mostly in the first 15 years of its growth).

Richard

[matt4x4]

I used to do this yearly on out front lawn, a witch with glowing eues, a couldren kept warm via a hotplate and a "fake" fire underneath, most parents were scared to step on out property, but that might have been because oif the lifesized "working" Guillotine i built which gets "remote controlled" by a friend hiding in the bushes - our display used to take up 2 front lawns (thanks to my old neighbours for the 2nd lawn) , now we're in the country with 5 acres and it takes up this little corner of our front lawn and is no longer as scary. Every year I build more, but I'll be 100 before I can get near filling THIS lawn!

[RavenNS]

Rotfl

You guys crack me up


Happy Halloween

[chem geek]

Here's a picture of the cauldron after having a large chunk of dry ice just added to it. The "hand" coming out of the cauldron is a nice touch, don't you think? Boil, boil, toil and trouble!

[chem geek]

So I tried leaving my pool open and the pH still stayed pretty much the same. I then realized that I could use my pool cover pump that normally pumps water off of the pool cover and could attach its output hose to a portable plastic shower that I have and put the pump into the pool (it's a waterproof pump -- essentially like a sump pump). I had to take off the shower nozzle because it gave too much resistance to the water and shut down the pump, but with the nozzle off I was in business. The stream of water hitting the pool surface from about 6 feet in the air has given enough bubbles and aeration to cause the pH to noticeably rise -- about 0.1 for every 8 hours of aeration starting from around 7.1

Though I could have just added some base, I thought I'd just try outgassing the same CO2 that I had added with the dry ice.

I hope everyone had a Happy Halloween.

Richard

[DaveD]

Here is a cheap way to aireate. Take a washing machine feed hose (about 1/2" id). Remove the coverplate and eyeball on one of the return jets from the pump and dry the cover plate. Use a copious amount duct tape to tape the hose so that end will be near the center of the eyeball and extend into the jet of water about 1-2" - you may need to form the hose slightly with some hot water so it points in the direction of the water flow. Don't tape around the back of the plate or you won't be able to put it back on. Put the coverplate and eyeball back in and lay the hose on the deck or rail of the pool. When you turn on the pump play with hose until you get the maximum amount of air coming out. You just made an eductor. You'll hear the air being sucked in and see a large stream of very fine bubbles. With this I could drive my alkalinity down in hours. Looks hokey, but heh - free and take it out when your done. And NO, I'm not red-green.

[chem geek]

Dave,

I'm just trying to visualize this. So the end of the hose that is in the jet flow is pointed so that the open end is pointing away from the wall -- that is, it is pointing towards the direction of where the water is going, is that right?. The water jet creates lower pressure around it (the Venturi effect) and that sucks air in from the other end of the hose that is on the deck. Though I can see how this would work by using a focused jet into an exhaust pipe outlet where a "tap" to the side just behind the output of the focused jet would be at lower pressure (i.e. a water eductor), I think that would require something more complicated than what I think you were describing. Have you tried this? How do you control where the water jet is flowing? I tried just using a flexible hose in the jet stream, but it doesn't lower the pressure enough to suck in air (i.e. to overcome the foot or two of water between the jet and the water surface). The hose tends to divert the jet flow so I suspect I am missing something about your description in terms of how you maintain the jet flow to be directed and concentrated so that it flows past the hose end without getting diverted or disrupted. I can see how this works readily in a water eductor that is quite common, but I'm missing something about how the duct tape and hose combination replicated this.

Richard