The elder Free-Ride offspring is lobbying to try an experiment this weekend. The working title of the protocol is "homemade soda*" but I suspect it may be described differently in the final report.
Dr. Free-Ride: Tell me about the experiment that you proposed to your teacher.
Elder Free-Ride offspring: I'll mix four cups of baking soda and vinegar and put each in its own bucket to keep the bubbles from spilling over, and take what remains in the cup and add fruit juice to it, and taste it, and if it's not sweet enough add sugar to it, and then pass it off as soda!
Dr. Free-Ride: Tell me more about the "what remains in the cup" part of your plan.
Elder Free-Ride offspring: The liquid from mixing the baking soda and the vinegar after all the bubbles go out?
Dr. Free-Ride: I know I don't let you drink soda very often, but what's one of the defining characteristics of soda when you open it and drink it?
Elder Free-Ride offspring: It bubbles over.
Dr. Free-Ride: If you open it and pour it carefully, it shouldn't bubble over.
Elder Free-Ride offspring: There are bubbles in it.
Dr. Free-Ride: So, do you think vinegar and baking soda together are going to taste like soda? Or are they just going to give the visual appearance of soda?
Elder Free-Ride offspring: They're going to give the appearance, but that's why we're adding the fruit juice and the sugar.
Dr. Free-Ride: You think that will taste ... adequate?
Elder Free-Ride offspring: Mmm-hmm.
Dr. Free-Ride: Do you know how they normally make soda water bubbly?
Elder Free-Ride offspring: By adding carbon dioxide to it.
Dr. Free-Ride: Yes. So we're talking about dissolving a gas in the water versus here, you're proposing mixing a weak acid and a weak base in the water. What happens when you mix an acid and a base?
Elder Free-Ride offspring: A chemical reaction happens.
Dr. Free-Ride: Yeah, I know. Do you know what the products of that chemical reaction are?
Elder Free-Ride offspring: Well ... a solution, I think, and sometimes, a salt.
Dr. Free-Ride: Yeah, a dissolved salt. And it's true that cans of soda will list their sodium content -- they do have dissolved salts in them. I guess the question is whether the stuff that bubbles out when you mix the vinegar and the baking soda -- whether the reaction leaves enough gas dissolved in the solution, or whether it just gives the appearance of gas (while it's reacting).
Elder Free-Ride offspring: Well, I want to try it this weekend and do a taste-test.
Dr. Free-Ride: And your teacher said this was a good idea?
Elder Free-Ride offspring: Well, she said it would be edible but it probably wouldn't taste good, and that she encouraged me to try it.
Dr. Free-Ride: I guess you should, then.
I'm going to make sure we have some carbon dioxide chargers handy so we can try more traditional methods, too. Also, some towels in case of spit-takes.
*I guess this means the California vernacular term for a carbonated beverage is "soda". You should feel free to substitute your own local term (pop, soda pop, seltzer, Coke, etc.) when you try this experiment and home and notice that the resulting solution is nothing like [local vernacular term for carbonated beverage].
You guys should do a biology experiment and make real soda. All you need is water, flavoring, sugar, yeast and a sealed pressure safe container (used plastic soda bottle works well)
Then you can go through the chemistry of how yest makes C02 from sugar!
Well, using baking soda + acid should work to get carbonic acid into solution. (Although there are probably better choices than acetic acid, citric acid comes to mind.)
The real problem is that the proposed method has the containers open, so it isn't going to stay in solution. The fix for that is obvious, but somehow I think that a proposal to perform the reaction in a sealed vessel would result in a very rapid no from both the teacher and the good Doctor.
 Suggestion for experimental variation: Using different acids, obviously sticking to acids found in foods.
This reminds me of how some people I knew, 20+ years ago, tried to make homemade root beer.
They got the flavoring syrup and mixed it with the proper amount of water ... and then, for "carbonation", dropped several large cunks of dry ice in it.
The result? Flat, lukewarm "root beer".
At least they didn't try to lid the container after putting in the dry ice.
I propose just adding fruit juice and sugar to any liquid you happen to have handy (food products only... this will be gross enough) and see if it tastes like soda pop.
Go right through the entire kitchen. Vegetable oil, Milk, can of Campbell's Tomato Soup....
Well, I've often pondered the easiest way to make my own carbonated beverages. Thinkgeek has this for sale, which could be of some use if you wanted to pursue this further:
I brew beer as a hobby, and we do "force carbonation" to speed up the process (will save about 2 weeks in bottles). I use a 5lb C02 tank hooked up to an old school soad keg to carbonate 5 gallons at a time.
Other option is to add sugar prior to bottling and letting the yeast make the C02 (called Natural Carbonation, also referred to as 'Live" beer)
Ha. Great experiment, whether it works depends on how you define success. I don't think you will let elder get discouraged, as this is really good science.
Now after the experiment take an empty glass soda bottle, fill it with tap water to the brim. Place on kitchen counter, your realm. Put finger or thumb deep into bottle neck, and keeping suction pull upward steady and hard on the liquid. Hundreds of bubbles will race upward in the water. Why, may be a good thing for elder to figure out.
Did the Elder Free-ride Offspring "try it"? What resulted after this? *curious*
Would you allow an old-fashioned yeast ferment ginger beer? If you drink it up quickly it doesn't get very alcoholic at all - just don't keep it bottled for long.
We've used Alton Brown's ginger ale recipe a couple of times. Less vinegary than the alternative.
For the next go around you can make LN2 ice cream!