A high-schooler told me that his science teacher showed the class a demo with ice in different sodas. Only in Diet Coke, the ice deformed non-uniformly thereby proving that ice melts + corrodes in Diet Coke.
I haven’t had time to look into this myself. Is this true? And, if so, why wouldn’t the ice corrode uniformly? If anything, wouldn’t one simply observed it melted faster, assuming one can manufacture ice cubes of identical physical dimensions (and identical imperfections within)!
I doubt that there’s any sort of significant thermal reaction happening with the simple chemicals in cola or diet cola. Certainly not “corrosion,” which makes it sound as though something in the cola is eating away at the ice, instead of simply causing it to melt differently.
The most obvious difference between diet cola and regular cola is that of density. Regular cola is significantly denser, due to the sugars in solution. Aspartame doesn’t effect the density of the solution very much – diet cola is very nearly the same density as water.
Here’s where my profound ignorance of fluid dynamics may get me into trouble:
Is it possible that the different densities creates some minor differences in the way that the melting water mixes with the soda? Obviously, water is miscible in a hydrous solution of caffeine, phosphoric acid and sugar-- but might the melted water hang around the bottom surface of the ice cube a bit longer in regular Coke due to the higher density of the surrounding fluid? (Sort of like an aggregate of of little black-and-tans?) If so, you’d have little buffer zones of colder, just-melted water providing a little insulation from the surrounding soda, and preventing all those lovely little bubbles of CO2 tap-tap-tapping against the cubes, pulling warmer fluid against the same spots, effectively melting little pits and streaks.
If this is the case, you might predict uneven melting in Diet Coke, and smoother melting in regular Coke.
I don’t know nuthin’ 'bout ice or diet coke, but I do know that my SIL cleans her funky-looking coffee cups with coke. and Rum and coke on the floor will strip the wax off lickety-split! You have to wonder what that stuff is doing to you stomach! :eek:
It’s an interesting article, but there’s no information in it that might shed light on why ice melts less uniformly in diet Coke than regular Coke, if that is indeed the case.
My point being that I don’t think it does “corrode” in Diet Coke, I think the students witnessed a “normal” melting process. I think the teacher served up an UL with a twist.
Lets not get caught up in the word corrode. It’s got a few meanings, and the only one which applies here it the loose defintion which means an object is slowly worn away to nothing. Scientifically speaking it refers to a chemical reaction which isn’t occuring here.
As for what could cause it, tough to say without more information. There’s four factors that I can see having an effect.
Density: The Diet Soda, as mentioned by Larry Mudd, will have a different density than the regular soda and therefore will have different thermal characteristics.
Salinity: The Diet Soda will likely have a different chemical composition, most commonly it’s salt content. As you see every winter, salt will lower the freezing point of the fluid and cause the rate at which the ice melts.
Solubility: The different types of liquid will have different soluabilities. Meaning that the diet may have a different ratio of corbon dioxide in solution and/or a different solubity quotient.
Bouyancy: Ice may be more or less bouyant in Diet Soda and therefore a different proportion of it my stay in contact with the fluid versus the air. Heat transfer between the liquid will be faster than with the air.
All three factors will have a sizable inpact on the rate at which the ice melts. The rate at which ice melts can also change the dynamics of that melting which could make the ice appear to be doing melting differently when all it’s doing is melting faster or slower. None of these factors are independant of one another and predicting what will happen is difficult to do.
Still, it sounds like the teacher and student in question have a flawed experiment if they are assuming that ice melts in a variety of liquids at the same rate. Every ice cube is different. Every fluid is different. The chemistry taking place is pretty basic high school material.
Additional the pH between each fluid is different, however I don’t expect that to play much of a role in the thermodynamics here. Still, it’s worth noting.
Ice does not corrode. That is a process of chemical attack on a metal. Did the student/science? teacher mean melt non-uniformly?
Perhaps the experiment, if any, of melting ice cubes in plain and diet coke were not well controlled and/or observed.
The freezing process of the ice cubes was not consistent?
You’re almost right. Sugar acts as a mild anti-freeze, and thus sugared sodas freeze at a tad below 32degrees F/0 degrees C. While diet sodas freeze ore or less at the freezing point. I know this as when I was a security guard in a building they gave me a key to the soft-drink machine. The machine was set as cold as possible. Thus TAB and Fresca (mostly Fresca) would come out semi-frozen, kinda like a slushy. Kinda tasty in fact. Beer and sugar soda can be kept around 30degrees F without freezing, and DAMN they are cold then!
Perhaps carbonation has something to do with it also. Maybe CO2 bubbles clinging to the ice offer spots of insulation, causing uneven melting.
That would apply to a wider range of colas, but whoever noticed this phenomenon (if it truly happens) may not have realized that it extends to other carbonated beverages.
The can of Coke Zero I’m holding right now lists the sodium at 40mg. Can’t say about the others, and the info is mysteriously elusive on Google, but I’d be a little surprised if canned Diet Coke and Coke were really sodium free.
In the spirit of the SDMB, surely someone has cans of both regular and diet Coke at home and can make the experiment? While ice cubes may be somewhat variable in size and shape, actually doing the experiment might give us some insight into whether this supposed phenomenon actually occurs, and if there are differences what might be the explanation.
I’d do the experiment myself, but then I’d have to drink the Coke.
Interesting. Burger King lists a large Coca-Cola at 5mg sodium, while a large Diet Coke has 25mg. Assuming large is the same at both vendors (714gm at BK vs. 32fl. oz. at McD), I wonder why different vendors would have different formulations?
