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In article <17hqh4INNsvb@darkstar.UCSC.EDU>,
          haynes@cats.ucsc.edu (Jim Haynes) writes:

> Why is it that adding table salt to soda pop causes foaming?  What's
> the chemical reaction (or is it all physical)?

i would imagine that crystals added to a solution supercharged with
gas would provide a great source of cavitation nuclei (minute cracks
from which bubbles would grow due to vapor pressure differences
overcoming the surface tension at the gas-liquid interface).

you can test this 'physical' theory by tossing sand, sugar, or
or whatever into some soda. i don't have any soda in the apartment
and _won't_ waste a beer . . .

ming
.sig under destruction

In article <1992Aug27.094131.1264@guvax.georgetown.edu>
cfhammer@guvax.georgetown.edu writes:
>In article <17hqh4INNsvb@darkstar.UCSC.EDU>,
>          haynes@cats.ucsc.edu (Jim Haynes) writes:
>> Why is it that adding table salt to soda pop causes foaming?  What's
>> the chemical reaction (or is it all physical)?
>
>i would imagine that crystals added to a solution supercharged with
>gas would provide a great source of cavitation nuclei (minute cracks
>from which bubbles would grow due to vapor pressure differences
>overcoming the surface tension at the gas-liquid interface).
>
>you can test this 'physical' theory by tossing sand, sugar, or
>or whatever into some soda.

     There are two possible ways to explain this phenomenon:

	  1) The increased ionic strength of the solution due to the
	     dissolving salt is making the gas less soluble.
          2) The salt is providing nucleation loci (as suggested by
	     Jim).

     If (1) were the case, this would only work with soluble substances
and the effect would depend on the rate of dissolution; if (2), any
granular solid that sinks in pop will produce the effect.  In either
case, sand is an ideal test substance (again, as Jim suggested).  I did
the experiment with sand a few years ago and got essentially the same
result as with salt.  Added to the observation that the salt doesn't
visibly dissolve in the time required for the reaction to take place, I
conclude that only (2) is important, i.e. that in this case, as in many
others, the effect is not strictly thermodynamic in origin and has a
substantial kinetic component.

				Marc R. Roussel
                                mroussel@alchemy.chem.utoronto.ca

The reason soda foams when salt is added has to do with the one ion
species forcing the other out of solution.  I used to know more about
it, but seem to have forgotten it.

Kurt Thorn