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Tom's Dumb Question: Salt Water Chills Beverage Faster?

   From Tom Shroder:

   Welcome to Tom's Dumb Question, Science Fair Edition. If anyone has invented a way for an adult to feel dumber than "helping" a child with his/her science fair project, I am unaware of it. Anywho, my son's project is on the fastest way to cool bottled beverages using ice and various water
solutions. We compared ice and plain water, salt water and water with alcohol. The salt water cooled furthest and fastest. We understand, or WILL understand once we decode all the stuff we downloaded from the web, why salt water has a lower freezing temperature than fresh water. But we
couldn't find anything to explain why salt water would cool FASTER than fresh water, given the same starting temperature and the same amount of ice dumped into the water. Anyone?

    [From JA: Tom, based on your description of the experiment, I'm assuming the various water solutions are of a fixed temperature, carefully calibrated, and that you can carefully monitor the speed at which the bottled beverages get cool when immersed in aforementioned solutions. Probably you have special NASA instruments and an atomic clock and stuff like that. Your results are expressed in Universal Time. I'd like to see a schematic of the experiment, along the lines of one of those Miller-Urey graphics. I don't know why the salt water conducts the heat more quickly from the bottle, but I bet it has something to do with the clathrates. Someone out there will explain all this in the boodle.]

By Joel Achenbach  |  January 12, 2006; 7:49 AM ET
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Everything you need to know about science fair projects is summed up in this sentence, which may or may not have been first uttered by Yogi Berra:

"In theory, theory and practice are the same. In practice, they are different."

Posted by: Reader | January 12, 2006 7:59 AM | Report abuse

sounds like tom has never made old-fasnioned ice cream - with the crank and the rock salt...

Posted by: ot | January 12, 2006 8:38 AM | Report abuse

Didn't you take any courses in the academically demanding departments at Princeton, Achenbach, like physics or math, or did you just get by hanging out with Oates and Morrison? Salt water has a lower freezing point (`ideal' solutions have this property, due to entropy (just counting possible states for mixtures as opposed to pure liquids)) so adding salt to water means that more of the ice melts than water freezes --- the system is no longer in equilibirum at 0 C. Well, if more of the ice is melting, that means it has to absorb the required latent heat of melting from the environment, so your bottles cool down faster since they are providing the required latent heat. At least, I think that's right, but having only gone to Princeton as a graduate student, I didn't have the benefit of CAP alumni as role models. Come to think of it, I'm pretty sure CAP would not have approved of my presence at Princeton at all. Off-topic, I am not sure why the idiot Democrats don't ask plain questions - how hard is it to say `Were you lying then or are you lying now?' with respect to any number of Alito documents? And Biden should be shot. Why anyone thinks this plagiarizing windbag is a viable candidate for President is beyond me.

Posted by: princeton-party-school | January 12, 2006 8:47 AM | Report abuse

Methinks it has much to do with conductivity, ions--sodium and chlorine, and electrolytes, and how clean or dirty is the water you are using.

Perhaps this link will help...

Wouldn't you rather be experimenting with Miyamizu instead?

Making good sake requires good water. Since ancient times, good Japanese sake has depended on the water, rice and climate. "Miyamizu" (shrine water) of Nada, Hyogo Prefecture in Japan is famous as the perfect water for fermentation of sake, and it is said that the technological factors behind Nada's success in the sake industry have been its highly polished rice and use of Miyamizu. When conductivity is calculated from the quality table of Miyamizu, it becomes 600 µS/cm, which means that is delicious water. It is further said that Miyamizu was discovered by Yamamura Tarozaemon, an ancestor of Sakura Masamune, in 1840. Tarozaemon carefully examined the difference of taste from one place of fermentation to another, and through trial and error by changing chief brewers and comparing methods of fermentation, he finally found the water to be a key factor in the taste of sake. Today, it is clear through analysis of Miyamizu which components in the water affect fermentation, and more and more brewers have came to use water that is appropriate for sake fermentation. Still today in Nada, Miyamizu is used, and the region takes great pride in the taste of its sake. Naturally, when making whiskey, wine or beer, there are differences in taste and color, depending upon where they are produced and what kind of water is used. The famous Munich black beer uses hard water, and Pilsner light-colored beer uses soft water.

Posted by: Loomis | January 12, 2006 8:48 AM | Report abuse

Hmm. I was thinking the same thing about homemade ice cream and rock salt.

I'm gonna take a couple of quick stabs at the question here, then think about it awhile.

1. We know salt water is more conductive of electrical energy than regular water.

2. I'm thinking about thermodynamic inertia. A steady state system requires more energy to change a given amount than a system that's already changing. The process of dissolving salt in water puts the system out of equilibrium, making any other system change require less energy (i.e. more efficient). Umm, right?

I think an improvement in conductivity and the themodynamic equilibrium, might cover it.

When I have some time, I might do some homework...


Posted by: bc | January 12, 2006 9:09 AM | Report abuse

Ah, I see I've BOO'd here.


Posted by: bc | January 12, 2006 9:15 AM | Report abuse

I don't know; I'll ask my 12-year-old daughter when she gets home from school. She's much smarter than I am.

But I better ask quickly, because her teacher told the class that after the "Winter Break," they would be preparing for the aptly named SOL tests (Standards of Learning), Virginia's answer to No Child Left Ahead. That means that between now and May, her accelerated-learning class WILL LEARN NOTHING NEW.

Posted by: TBG | January 12, 2006 9:19 AM | Report abuse

the short answer is: melting ice absorbs heat from its surroundings, and adding salt makes ice melt faster.

Posted by: omnigood | January 12, 2006 9:21 AM | Report abuse

Was the ice obtained from the Titan probes?

Posted by: Scottynuke | January 12, 2006 9:23 AM | Report abuse

We're all missing the *Really Important Question*, here: can the technology be harnessed in time to get our beer really cold in time for the football game (or 10am this morning, whichever comes first)?

Posted by: byoolin | January 12, 2006 9:26 AM | Report abuse

The comment about latent heat (technically, "heat of fusion") and depressed freezing point is correct.

The introduction of salt to the water creates a solution whose freezing point is lower than 0C. Pure water ice in that solution is no longer thermodynamically stable and so it melts. However, it takes energy to do that. The energy comes from the heat supply of the salt solution, and anything in contact with the salt solution (like a can of cold, refreshing, malt beverage), lowering the temperature. Water takes a lot of energy to change phases. If you can force a phase change by adding salt, then the increased melting rate of the ice means an increased heat-loss rate from anything in contact with the ice, as energy is consumed in the melting process.

If the background environment were held stable at the freezing temperature of the target salt-solution, then the salt and ice could coexist comfortably together with no melting, because there would be no energetic advantage to melting and refreezing. Salt solution melts ice only if there is a heat reservoir at a temperature above the freezing point of the salt solution.

Posted by: ScienceTim | January 12, 2006 9:28 AM | Report abuse

On a side note, I noticed this little tidbit from the AAS yesterday, Gugliotta picked up on it.

Lessee, things we thought were true constants over time but have found evidence that they may not be:

Speed of light
Dark energy/Cosmological constant (not)

Please make it stop, or I'm going to start losing sleep.


Posted by: bc | January 12, 2006 9:29 AM | Report abuse

The atmosphere of Titan is cryogenic. Michael Jackson has expressed interest in investment opportunities, as well as establishing his own shrine upon Saturn's moon. He already made it to our moon, his "moonwalking" as famous as Neil Armstrong's.

Posted by: Loomis | January 12, 2006 9:30 AM | Report abuse

I'm not as smart as Tom's kid. When I wanted to cool some beer quickly in grad school, I went for overkill, and tried to use liquid nitrogen. It would have worked, if we had cans. It also turns out not to work if you try to addd liquid nitrogen directly to the beer. Frozen beer foam everywhere.

Posted by: ScienceTim | January 12, 2006 9:30 AM | Report abuse

Hmph. In college, I was fine with room temp beer, especially if it was free.

Sure, I preferred cold, but beggars can't be choosers.

Warm beer + cold pizza = The Breakfast of Champions.


Posted by: bc | January 12, 2006 9:36 AM | Report abuse

Since Science Tim has checked into the Boodle this morning, I have two questions:

How did you become interested as a young boy, or a young man, in studying the heavens/sky/stars/solar system/galaxies/etc.? A mentor, a book, a camping experience, laying in the grass at night, looking up?

How does poetry find the astrophysicist, or vice versa (since Tim, you've shared two with the Boodle thus far..)?

(This would be a good question for bc, too, since you are interested in the cosmos, and I thought your Alito poem yesterday was a fine one--so interesting to see a tab at your website titled "bc's Playhouse.")

Posted by: Loomis | January 12, 2006 9:41 AM | Report abuse

I too used to drink room temperature beer in college. Of course I'm talking a basement room temperature of 58°. Oh yeah, and the beer was actually an english ale. Mmmhmhmhmmm.

Posted by: omnigood | January 12, 2006 9:52 AM | Report abuse

Not wanting to obscure SciTim's answer, but since I have an extreme science bent as well, I'll offer an answer, Loomis.

My dad's a retired electrical engineer, and he filled the house with science books of many stripes. He tended to tune to PBS regularly as well, so my TV evenings were often filled with "Nova" and "Cosmos" and such. Probably explains why I wrote a report on black holes in middle school.

Posted by: Scottynuke | January 12, 2006 9:54 AM | Report abuse

*slapping forehead*

We obviously forgot to ask JA to ask Tom what beverages they were cooling... Would beer lose heat faster than soda?

Posted by: Scottynuke | January 12, 2006 9:56 AM | Report abuse

WOW, not two hours after Tom posts a dumb question JA puts up another Kit. Looks like JA is figuring out this scheming thing quite well.

Posted by: omnigood | January 12, 2006 9:58 AM | Report abuse

Now, Scottynuke's question is a more difficult one (heh heh). You need to do some fluid mechanics for this one, since the temperature gradient introduced in the can causes fluid flow that will depend on the density and viscosity of the fluid. The convective flow, and hence the rate of heat transfer, will depend on how the can is oriented with respect to gravity. I don't think this can be solved analytically. For American beer, it probably doesn't differ very much from soda. On the other hand, for the real stuff (Guinness!) it probably is a bit different.

Posted by: princeton-party-school | January 12, 2006 10:06 AM | Report abuse

I had to chop down a lovely old mimosa tree because its roots were making cracks in my concrete porch floor. This was a shame too because of the lost shade and my black cats looked so pretty napping in its branches nestled among the pale pink blooms. Anyhoo, cutting down the tree doesn't kill the roots; it makes them stronger. A box of rock salt melted in boiling water and then poured over the freshly cut trunk destroys the root system.

Posted by: Nani | January 12, 2006 10:14 AM | Report abuse

SCC but I don't know why. Science Tim?

Posted by: Nani | January 12, 2006 10:20 AM | Report abuse

Just a side comment... Experiments involving heat flow and temperature ('calorimetry') are notorious among physical scientists for being hideously difficult and error-prone. It's remarkable that Tom got a result that was plausible, and possibly even correct.

Posted by: Matt | January 12, 2006 10:57 AM | Report abuse

From the kit: "We compared ice and plain water, salt water and water with alcohol."

In the interest of science, what kind of alcohol? Scotch, perhaps?

Posted by: Bayou Self | January 12, 2006 11:36 AM | Report abuse

This is one of those science fair type of experiments that is pretty meaningless, because it is not testing any type of hypothesis based on an observed phenomena. You have no idea whether salt water should freeze faster or not and if so why. All you are doing is making observations. The whole science fair schtick bothers me because 95% of the kids are doing things like what shape rock falls faster and the kids with science connections are doing things like Effects of Various Nutrient Concentrations on the Cloning of the Eye of Solanum tuberosum at Multiple Stages and "Fractal Dimension Analysis of Putative Martian Coastlines.". (real national winners of different science fairs)

In my engineering world, we freeze regular water and we boil salt water, so I have much better information on that stuff. But here is what little factual information I do have:

The freezing point of regular water is 32 deg F (duh) and the freezing point of a 20% sodium chloride solution (a lot of salt) is 2.3 deg F. Water has a density of 8.34 pounds per gallon. 20% salt water weighs 9.6 pounds per gallon. That mixture consists of 1.92 pounds of salt and 7.68 pounds of water.

The specific heat of water at room temperature is 1.0 Btu/lb*degF. The nice round number is not a coincidence. The definition of a British Thermal Unit is the energy required to raise the temperature of one pound of water one degree Farenheit. The metric unit, the joule, is defined the same way except with a gram of water and degrees Celcius.

The specific heat of our salt water is only 0.813 Btu/lb*degF, so it should cool faster. However it has to cool all they way down to 2.3 degrees before it freezes. Water needs 333 Btu to get from room temperature to freezing, Salt water is going to need 544 degrees.

It takes 144 Btus to freeze a pound of water without changing its temperature. This is called the latent heat of fusion. Beyond this point, I am no longer credible since I have no documentation on this stuff. If the salt does not affect the latent heat of fusion (which is a big if) it takes 1196 Btus to freeze our 8.34 pound gallon of pure water, but only 1101 Btu to freeze our 7.68 pounds of water that are in the gallon of salt water.

So the total cooling required to freeze our room temperature tap water is 1529 Btus. To freeze the salt water it probably takes about 1645 Btus. At a constant rate of heat removal, the salt water should take 7.6% longer to freeze, which contradicts your observation.

This is all fraught with a lot of assumptions. 20% salt water is very very salty. You are probably using a much weaker concentration and the differences are going to be much smaller. I doubt the freezer you're using is holding below 10 deg F, which means it can't even fully freeze the concentrated salt water. This needs to be done in sealed containers to prevent evaporation from affecting the results. Since water expands as it freezes (it's most valuable anthropic property), Whatever you freeze it in will probably burst.

I know someone has read this far and is rolling there eyes in amazement and mumbling, "This dork has no idea what he's talking about." And I agree. Anything involving phase change is thermodynamically and even chemically very complicated. Way beyond the ability of a middle school science fair project to address meaningfully.

And don't end up making any ice-9 by mistake, or we are all goners.

Posted by: yellojkt | January 12, 2006 11:44 AM | Report abuse

If you look at the USGS stream gage site for the NW Branch of the Anacostia River at you can see that the conductivity spikes to be above 1800 µS/cm on December 12, because of snow related road salt entering the creek.

Unfortunately the monitoring program stopped at the New Year because of lack of funding.

Posted by: Mike | January 12, 2006 11:48 AM | Report abuse

I think Global warming will take care of Ice-9 just fine.

Posted by: omnigoof | January 12, 2006 11:51 AM | Report abuse

Okay. Science Tim and others answered this question very well, but let me try to put it into slightly different language.

Ice is like a bunch of frat boys talking to one another at a party. They enjoy hanging out together, but if they get too warm the heat will make them wander around aimlessly in search of a cool breeze. This is melting. The warmth comes from the bottles you are trying to cool. Salt is like a pretty girl. Once she shows up, the frat boys desperately want to all cluster around her, pushing and shoving to get a good look. But they need heat to do so, so they get the heat from the bottles. Just as quickly as they can. This is also why salt water is harder to freeze. The frat boys are loath to abandon the pretty girl and will put up a fight until the last little bit of energy is taken from them. Then they grudgingly start to hang out together again.

(By the way. I have been told that I can post from work, as long as the postings are inconsequential. Which pretty much describes everything I write.)

Posted by: RD Padouk | January 12, 2006 11:57 AM | Report abuse

I misunderstood the project altogether. I thought you were freezing ice water. You're using ice water to cool other things. That's much easier. Ice is going to be whatever temperature it is in your freezer, usually 0-20 def F. Ice melts when it reaches 32 deg F. The ice is not actually cooling the can or cup (for our puposes let's assume a can). The cold water the ice is sitting in is using convection and conduction to cool the can. Salt water freezes at a much lower temperature (2.3 deg for 20% salt), so the ice/salt slush stays colder.

The rate of heat transfer from the ice to the can is given by:
where Q is the amount of heating or cooling (you are either cooling the can or heating the ice, dpending on your perspective).
h is a heat transfer coefficient that depends on the fluids and the geometry.
A is the area of the can in the ice.
dT is the temperature difference between the ice slush and the inside of the can.

Since in a well designed experiment h and A are kept the same, the dT changes.

Since salted ice is colder than regular ice , Q or the rate of heat taken from the can is higher and faster.

The usual caveats about thermodynamics being more than one algegra equation apply.

Posted by: yellojkt | January 12, 2006 1:49 PM | Report abuse

Practical science project idea: Keep one thermometer in the ice water to document brine temperature versus cooling time.

Posted by: yellojkt | January 12, 2006 2:27 PM | Report abuse

yellojkt, Science Tim... less verbose please, and the original problem only.

Why does salt water freeze FASTER than regular ol' water? Like a bunch of boodlers said, there's not enough information about the temperatures used, etc.
Lost in the gibberish was the basic point: Phase change takes energy.

Let's assume that normally equal volumes salt water and regular water in identical beakers cools equally (same heat capacity).

This no longer holds true when water nears the freezing point. Water's heat capacity (I hope this term is right) shoots up, because it needs to suck/retain heat to form ice crystal lattices.
So it cools/heats slower right around the phase change.
Salt water doesn't do this at around 32 F because it has a lower freezing temperature. Therefore salt water won't slow down its cooling until it's at a much lower temperature.

An introductory physics book might give you the information needed, and you can have fun calculating the kcal required for phase changes of water versus cooling/heating. Poor kid.

Posted by: Wilbrod | January 12, 2006 2:38 PM | Report abuse

Tom - you might want to modify the frat boy analogy for your offspring - but I still think it's fundamentally sound. I hope in your research you find reference to water atoms as "Mickey Mouse" atoms. That's always fun.

To all - remember this is a kid's Science Fair project. The idea is to help Tom explain the underlying concepts to his child. As someone who has judged such projects, I despise seeing kids with nifty charts and complicated equations but do not get the underlying principles. A very wise chemistry professor once told me that chemistry is about thinking about things on a molecular level. In the Feyman Lectures on Physics he makes basically the same point.

Tom - get your child to think like an atom. All else will follow.

Posted by: RD Padouk | January 12, 2006 3:11 PM | Report abuse

Exactly right RD Padouk, this is a kids science fair project. I still hold that my answer is the truest and best:

the short answer is: melting ice absorbs heat from its surroundings, and adding salt makes ice melt faster.

Posted by: omnigood | January 12, 2006 3:19 PM | Report abuse

This Kaboodle is amazing. You'll all share in the "A", if my son manages to get his project board in on time. We thank you.

Posted by: Tom | January 12, 2006 4:38 PM | Report abuse

If I may go (slightly) off-topic, check out this guy who built a jet-powered beer cooler. Very cool (yuck-yuck).

Posted by: digs | January 12, 2006 8:31 PM | Report abuse

Okay, first timer here, but I think there's a simpler explanation than I've read so far. The brine is colder than the ice water. That's it. No need to invoke phase change. You could get the same effect by putting an ice-free brine straight into the freezer and then starting the experiment when the brine has reached the same temperature as the ice in there.

Ice water is stuck at 32 F until either all the ice melts or all the water freezes (whichever direction you're going). The brine can be colder than the ice water because it freezes at a lower temperature.

Posted by: Alf O'Mega | January 13, 2006 11:10 AM | Report abuse

It looks like you've all been snookered. Tom isn't talking about sodium chloride, he's talking about using the Strategic Arms Limitation Treaty. Obviously when you expose alchohol to the liquid oxygen in the ballistic missiles, everybody freezes. In terror perhaps, or more likely awe as one drunkenly watches the contrails of the ICBM heading towards the beginning of the end.

Posted by: PeterK | January 13, 2006 11:23 AM | Report abuse

wow that was alot of information that helped with my project.

Posted by: jasmine | January 15, 2006 3:10 PM | Report abuse

There are a couple of really good posts on colligative properties of solutions. The salt lowers the melting point and further cools by absorbing heat to dissolve in water. That is why it is colder and cools faster.

But the most innovative aspect of your experiment is using this blog for private education sending your son to a good private school where he would learn all this in class, at much greater expense notabene. Hear hear!

Posted by: AgentG | January 18, 2006 8:16 PM | Report abuse

Can I make 5F water by taking 20F ice and mixing it into a brine solution that I keep at 20%?

Posted by: Randy | July 27, 2006 10:26 AM | Report abuse

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