soda water

[elymir]

Why does sugar dissolve faster in soda water than regular water. Is it the action of the bubbles or the carbonic acid?

[EDS]

Why does sugar dissolve faster in soda water than regular water. Is it the action of the bubbles or the carbonic acid?

Hi elymir,

Good question! I'm a poor person to answer this; you probably know more wet chemistry than I do. But, I'll ask around and see if anyone I know has a good answer.

Intuitively, it seems like both effects could possibly be important.

Sugar molecules have slightly polar regions which can form temporary bonds with water molecules. If you add extra ions to the mix, one might imagine it having some effect on the interaction. (I don't know that it does, but it sounds plausible.)

On the other hand, the bubbles will almost certainly be important, both by mechanically agitating the surface of the solid and by moving the water around and spreading out the high sugar concentration near the surface.

You could also ask whether the dissolved CO2 molecules will have any effect. What happens when you try to dissolve two different molecules with tiny polar moments in wafer?

A couple experiments one might imagine doing to try to separate the two effects:

- Dissolve sugar in other acids with a similar pH but no bubbles. (Assuming there isn't some chemical reaction involving either acid and the sugar molecules.)

- Try to change the amount of bubbles. If you start with the same CO2 concentration and generate less bubbles, you're presumably got a higher concentration of carbonic acid (assuming the CO2 <-> carbonic acid reaction is fast enough). If the sugar dissolves faster, then the carbonic acid is dominant. If it dissolves slower, then the bubbles are dominant. For example, you could try dissolving similar sized and shaped crystals of rock candy mounted on a wire in bottles of room temperature soda water, one of which remains sealed while the other has been recently opened. Gluing the samples to the inside of half full bottles and then gently rotating them so as to submerge the crystal would allow you to perform the whole operation while one bottle remains sealed. (There may be complications that would cause trouble here - I don't know.)

good luck,
Erik

[Guest]

I think that the explanation for the sugar dissolving faster probably has to do with the carbonic acid. Basically what is happening is an acid/base reaction between the carbonic acid and the sugar. The sugar in this case is a weaker acid than the carbonic acid so it actually acts like a base, accepting a hydrogen atom from the carbonic acid. Any time a reaction like this can happen, it is going to increase the solubility of the solute (the stuff you added). In normal water, sugar dissolves because it is able to form hydrogen bonds with the water molecules. In the more acidic soda, the sugar can react with the acid giving the sugar a net positive charge. Whenever there are charged particles, water really likes to dissolve them, that's why salt dissolves so well in water. So the positively charged sugar dissolves more quickly.

[davidmoilanen]

Sorry, that last post was from me.

[EDS]

Sounds like the right person to answer this question happened by.

Thanks!

- Erik