Thread: mentos and cola

I'm not sure if the chemistry forum is the right place for this question but maybe someone can help. Why does cola shoot out of a 2 litter bottle when Mentos candy are dropped in?

JA Cambece
JA Cambece Law Office

Go here.

http://www.thescienceforum.com/Soda-...tion-2836t.php

I've yet to see a good explanation for this...there are a lot of different explanations out there, but none of them stand up to scrutiny.

The only thing I can say with certainty is that it’s an effect caused by the outer surface of the mento. If you dissolve the outer surface off, the soda explosion doesn’t happen.

the dissolved Co3 reacts with the salt in the menthos (taking an oxigen) and the Co3 Changes to Co2 what is a gass. This happened almost instantly, so a similar to boiling reaction occurs and the gass escapes simultainously.

Originally Posted by Zwolver

the dissolved Co3 reacts with the salt in the menthos (taking an oxigen) and the Co3 Changes to Co2 what is a gass. This happened almost instantly, so a similar to boiling reaction occurs and the gass escapes simultainously.

But the same thing doesn't happen in you drop a handful of salt into the soda.

Also, I think your chemistry is kind of fuzzy there. How does the salt "take an oxygen" from CO3?

Well... your theories aren't true

In 'Cola solution' gaseous CO2 is dissolved. When you put mentos into 'Cola solution' blistres of gaseous CO2 form on its surface. There's no chemical reaction rather coarse surface of 'mentos' facilitates forming blistres of gaseous CO2 ( new phase can be created more easily on coarse surface than on smooth surface).

Originally Posted by Neecze

Well... your theories aren't true

In 'Cola solution' gaseous CO2 is dissolved. When you put mentos into 'Cola solution' blistres of gaseous CO2 form on its surface. There's no chemical reaction rather coarse surface of 'mentos' facilitates forming blistres of gaseous CO2 ( new phase can be created more easily on coarse surface than on smooth surface).

Also doesn't make sense. If you drop any other coarse material into a bottle of soda, the effect doesn't happen. I suppose it's possible that there's something unique about the mentos surface that makes it perfect for nucleating gas bubbles, but it seemse unlikely to me.

If you drop any other coarse material into a bottle of soda, the effect doesn't happen.

Of course it does. Try to put a bar of sugar into glass of soda - you'll see that frequency of appearance of blistres of CO2 will increase.
Ok, behavior of bottle of Cola in experiment was very violent but it could be brought about presence some organic acids in mentos (for example citric acid which is used as a stabilizer of acidity).
Citric acid is more stronger than carbonic acid so that citric acid can easily displace carbonic one as its anhydride - CO2. Since ionic reactions are very rapid, pressure in bottle increases violently: gaseous CO2 can't escape from container freely therefore CO2 put liquid out.

That's my theory

Originally Posted by Neecze

Well... your theories aren't true

In 'Cola solution' gaseous CO2 is dissolved. When you put mentos into 'Cola solution' blistres of gaseous CO2 form on its surface. There's no chemical reaction rather coarse surface of 'mentos' facilitates forming blistres of gaseous CO2 ( new phase can be created more easily on coarse surface than on smooth surface).

This is correct.
It is not a chemical reaction.
The CO2 bubbles generated by, and formed around, the rough surface of the candy rise and, in effect, push the cola out of the bottle rapidly.

Originally Posted by Scifor Refugee

But the same thing doesn't happen in you drop a handful of salt into the soda.

Wrong, the same happens, but a bit less drastically. I found that out as a child. My parents weren't able to explain it to me though.

Originally Posted by oracle

Wrong, the same happens, but a bit less drastically. I found that out as a child. My parents weren't able to explain it to me though.

Yes, if you drop salt into soda it produces some bubbles, but it’s nothing like the effect of a mento. It doesn’t make sense that the bubbling from a mento is caused by salt when dropping a handful of salt in directly produces a much smaller effect.

I'm not sure what happens at the surface of the candy but whatever it is the result has to do with Einstein's explanation of Brownian motion. Another one of his theories led to the atomic bomb and now this!!

Cola is a supersaturated solution, molecules of CO2 being kept in solution by pressure. Open a can and they try to get out but are slowed down by the surface tension barrier. A similar reaction to Mentos happens if you pour the contents over very cold ice cubes. In this case the effectiveness of the barrier is reduced by temperature difference.
Presumably the mentos chemistry and surface structure destroys the barrier allowing release of gas that is collected between candies in the string, bouyancy drives the string up to partially block escape allowing pressure to build up until finally it lets go with explosive force.

Sorry didn't mean to stiffle debate by invoking the Great One. My ideas about interface diffusion are not accepted by mainstream climatology so maybe I'm wrong.

I will however tell you an experiment that demonstrates sudden breakdown of surface tension barrier.

Float a lighted candle on a substantial amount of water and hold a glass jar over it making a seal at the water. After a few moments the flame starts to fade and eventually goes out with a little whisp of smoke. Nothing happens for a couple more seconds then WHAM! the water jumps up to fill 1/5 the volume. The oxygen in the enclosed space is changed to CO2 and hot molecules are beating against the water until surface tension breaks and they escape into the liquid. It does not happen gradually.