caffeine=antifreeze?
mcdo...@hartwick.edu
Besides, it's about ingredients...
My fridge works very well. Let's say _too_ well. A bottle of Coca Cola (tm)
froze. Except this is caffeine free Coke. A bottle of regular, caffeinated
Coke didn't freeze.
The Coke is a 2/3 full, open bottle. Not flat though. The CF Coke is a new
unopened bottle that had a shaky ride home, and therefore may be under pressure
or something. But as I understand it, the pressure would _lower_ the freezing
point and therefore make freezing harder.
So... Is caffeine antifreeze?
Louis Hom
<mcdo...@hartwick.edu> wrote:
>
>My fridge works very well. Let's say _too_ well. A bottle of Coca Cola (tm)
>froze. Except this is caffeine free Coke. A bottle of regular, caffeinated
>Coke didn't freeze.
>
>The Coke is a 2/3 full, open bottle. Not flat though. The CF Coke is a new
>unopened bottle that had a shaky ride home, and therefore may be under pressure
>or something. But as I understand it, the pressure would _lower_ the freezing
>point and therefore make freezing harder.
>
>So... Is caffeine antifreeze?
>
the regular Coke not diet? You're right that a pure substance under pressure
has a lower freezing point. But I think that only means that the CO2 would
experience that effect, not necessarily the Coke mixture containing the CO2.
Since freezing point depression is a function of molality (a measure of
concentration), I kind of doubt the caffeine is the source of the difference.
Caffeine has a sizable molecular weight, and a pretty low concentration in
colas (well, your human colas at least).
Or does dissolved gas do something weird to freezing points that I
don't know about?
--
______________________________________________________________________________
Lou Hom "On that day did they all mingle blood with wine and
lh...@ocf.berkeley.edu drink it and when they had drunk themselves to mighty
drunkenness, they parted."
-- from _All Men Are Brothers_
Lin Nah
I don't think you want to freeze a closed can or bottle
of coke. very messy results ;)
lin
Steve Loring
>From: mcdo...@hartwick.edu
>Subject: caffeine=antifreeze?
>Date: 30 Nov 94 00:19:30 -0500
<deletion>
>My fridge works very well. Let's say _too_ well. A bottle of Coca Cola (tm)
>froze. Except this is caffeine free Coke. A bottle of regular, caffeinated
>Coke didn't freeze.
>The Coke is a 2/3 full, open bottle. Not flat though. The CF Coke is a new
>unopened bottle that had a shaky ride home, and therefore may be under pressure
>or something. But as I understand it, the pressure would _lower_ the freezing
>point and therefore make freezing harder.
>So... Is caffeine antifreeze?
There are unknown variables here, such as the cooling patterns of the
refrigerator and the formulas of the different soft drinks. Even though the
regular Coke was not "flat," it had lost considerable pressure by being open,
therefore also lowering its CO2 concentration. Freezing points are affected
by solute concentration (CO2 in this case), which already means the two
bottles are operating under different conditions (shaking the bottle up
doesn't change the overall internal pressure, but will affect how quickly--and
explosively--the gas comes out of solution when the bottle is opened and the
pressure suddenly lowered). A chemist I talked with said that caffeine is
not an antifreeze (for one thing, it's present in only mg quantities, too
little to have much effect on the freezing point). So, we're back to the
drink formulations, cool spots in the refrigerator, and pressure differences.
Steve
William Hodgeman Jr
> > But as I understand it, the pressure would _lower_ the freezing
> > point and therefore make freezing harder.
>
> on the freezing point of water and that it would be to raise it. I'm not
> sure, but since water expands upon freezing, I would guess this would be
> the case. Can anyone give a positive answer on this?
Increasing the pressure decreases the freezing point. The most often
quoted example for this is ice skates...the runner greatly increases the
pressure and causes the ice to melt thus the skate moves on a layer of
water. BTW, water is one of the very few substances that do this... melt
with increased pressure/expand upon freezing.
Bill
murphy kenneth p
John Widmann <wid...@u.washington.edu> wrote:
> > But as I understand it, the pressure would _lower_ the freezing
> > point and therefore make freezing harder.
>
>on the freezing point of water and that it would be to raise it. I'm not
>sure, but since water expands upon freezing, I would guess this would be
>the case. Can anyone give a positive answer on this?
>
John,
An increase in pressure will favor the phase with the smaller molar volume.
Hence if you raise the pressure you raise the boiling point, but for water you
decrease the melting point. Most liquids contract upon freezing and increased
pressure increases the melting point.
Regards,
Kip
--
Dr. Kenneth P. Murphy e-mail: k-mu...@uiowa.edu
Department of Biochemistry office: (319)335-8910
Univeristy of Iowa lab: (319)335-7936
Iowa City, IA 52242 FAX: (319)335-9570
john bollinger
> > point and therefore make freezing harder.
>
>on the freezing point of water and that it would be to raise it. I'm not
>sure, but since water expands upon freezing, I would guess this would be
>the case. Can anyone give a positive answer on this?
The effect of pressure on freezing point depends on the substance. (Remember
your T-P phase diagrams?) Water is unusual in that increasing pressure lowers
its freezing point; most substances have lower freezing points at higher
pressure. The reason that water is different from most substances in
this way is the same as the reason solid water floats in liquid water: the
solid is less dense than the liquid.
I doubt, however, whether the additional pressure in a soda bottle would
result in a sufficient difference in freezing points to explain the observed
differences for Coke and caffeine free Coke.
John Bollinger
jobo...@indiana.edu
john bollinger
>your T-P phase diagrams?) Water is unusual in that increasing pressure lowers
>its freezing point; most substances have lower freezing points at higher
Oops. I meant to say that most substances have _higher_ freezing points at
higher pressure. Sorry.
John Bollinger
jobo...@indiana.edu
Gary Heston
[ stuff about freezing/pressure deleted ]
>I doubt, however, whether the additional pressure in a soda bottle would
>result in a sufficient difference in freezing points to explain the observed
>differences for Coke and caffeine free Coke.
Maybe not--but placement in a refrigerator can certainly make a difference!
I've had lots of stuff in the back freeze when stuff inches away didn't
show a trace of ice.
Besides, there is a significant difference between placing a material
*under pressure* and a carbonated beverage or whatever--the carbonated
liquid isn't really *under* pressure, it's a mixture of gas and liquid
which will act differently (I suspect the gas molecules will cause the
liquid molecules to be more separated, and make it harder for them to
link up, but I'm no physicist).
--
Gary Heston, at home..... ...which is now running Unix... :-)
ga...@cdthq.uucp uunet!sci34hub!cdthq!gary ga...@cdthq.uucp@uunet.uu.net
"Knowledge accumulates in universities, because the freshmen bring a
little in, and the seniors take none away." Academic saying
Jeff E. Janes
:
: Increasing the pressure decreases the freezing point. The most often
: pressure and causes the ice to melt thus the skate moves on a layer of
: water. BTW, water is one of the very few substances that do this... melt
: with increased pressure/expand upon freezing.
:
: Bill
However, in order to increase the pressure, CO2 must leave the solution,
entering the gas phase, which would lower the dissolved gasses in the
Coke. Less gas should mean higher freezing point (colligative properties)
I would guess that this would far outweigh pressure effects.
jeff
p.s. The ice skating example is very controversial. My High school physics
teacher and college P-chem prof both gave this as the basis of ice-
skating, while my High school physics text and college p-chem book say
this explanation is bunk, that the effect is very minor.
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Jeff Janes at Michigan Tech,no logical University +
+ jej...@mtu.edu +
Anthropomorphism: recommended by 9 out of 10 organic molecules
john bollinger
>Maybe not--but placement in a refrigerator can certainly make a difference!
>I've had lots of stuff in the back freeze when stuff inches away didn't
>show a trace of ice.
I have seen this too. It is a more likely explanation than the
pressurization.
>Besides, there is a significant difference between placing a material
>*under pressure* and a carbonated beverage or whatever--the carbonated
>liquid isn't really *under* pressure, it's a mixture of gas and liquid
>which will act differently (I suspect the gas molecules will cause the
>liquid molecules to be more separated, and make it harder for them to
>link up, but I'm no physicist).
I have to disagree with you here.
First of all, your view of the nature of CO2 in water is mistaken. CO2
does not exist as "gas" molecules or even gas bubbles in carbonated water;
rather the CO2 is dissolved in the water, and affects the water like any
other solute. (Which is to say reduces the freezing point and increases
the boiling point, among many other things.) The microscopic description
you give is similar to the generally accepted explanation for these
effects.
Second, the liquid really is under pressure. 1) Anything not exposed to
vacuum is under pressure. 2) The liquid in a sealed soda bottle is under
_increased_ (read "greater than atmospheric") pressure. The
concentration of CO2 in carbonated water is greater than the solubilty of
CO2 in water _at_atmospheric_pressure_. Thus CO2 evaporates into the
head space above the liquid until its vapor pressure above the solution
is sufficient that the solution is at equilibrium. This pressure is greater
than atmospheric. That is why you hear a hiss when you open a bottle or
can of a carbonated beverage, and why champagne corks shoot across the room.
Dr. John Bollinger
jobo...@indiana.edu