Science Buddies: "Ask an Expert"

Hello Experts

Looking for a scientific/mathematical solution to the Baking Soda & Vineagr trick for my son.

Here's the background: He (we) are putting together a project he has for school. We're using 2 liter bottle, pouring Vinegar inside bottle w/ a few drops of food coloring(this is for eruption effect) then pouring in baking soda & bam it erupts...he is calling it Fizz Mountain.

Is this anything more than a chemical reaction? Part of the assignment is to have the scientific or mathematical solution...looking for help in that area.

Thanks for your help

Hi Nascar4,
Welcome to the Ask an Expert forum.
This classic demonstration of a chemical reaction is actually a two-step reaction. In the first step, the acetic acid (in vinegar) reacts with the sodium bicarbonate (baking soda) to form carbonic acid and sodium acetate. The chemical equation for this reaction is written like this:
HC2H3O2 (acetic acid) + NaHCO3 (sodium bicarbonate) => H2CO3 (carbonic acid) + NaC2H3O2 (sodium acetate)

In the second stage of the reaction, the H2CO3 (carbonic acid) breaks down into water and carbon dioxide:
H2CO3 (carbonic acid) => H2O (water) + CO2 (carbon dioxide)

The formation of the carbon dioxide (CO2) bubbles (known as "exsolution") is what creates the dramatic fizz.

I hope that helps,
Chris

Thanks for your help.

My ds class has not got deeply involved in the scientific formulas. So, if we use something like this as a scientific solution would it be correct :

"The trick of using household products of baking soda & vinegar is a chemical reaction. Start with vinegar & add the baking soda & then the chemical reaction with the two items creates a carbon dioxide which is why there is fizzing out of the bottle."


As part of his project he has to state the scientific or mathematical solution to his trick. Would the above scenario work for him??

Thanks again
Lisa

Lisa,

I think that the "scientific solution" you have posted is completely acceptable for someone in a middle school science class. It hits the main point: the fizzing and foaming is the result of chemical reactions between the vinegar and baking soda. You may want to change "a chemical reaction" to "two chemical reactions", but that may be getting a bit picky. The most important thing here is that your child/student explains the scientific solution using concepts that he understands in his own words.

Best of luck with the project; let us know if we can be any more help!

In addition to the two chemical reactions in solution involved that starts with a liquid and a solid powder that yields a gas by product, there are physical and thermodynamic things going on as well.

If you are just pouring a quantity of baking soda powder into the top of a 2 liter plastic soft drink bottle, the rate at which the chemical reaction starts is poorly controlled. In order for the reaction to occur, the solid has to make contact with the liquid and disolve.

The surface area of the liquid in the bottle is larger than the cross section of the top opening. This means that the flow of gas will undergo a Bernoulli dynamic fluid flow compression process. If you cut the top of the bottle off just below where it starts to round over and get smaller, and compare results, I would expect significant differences in the rate and volume of overflow of liquid.

Bubble surface tension properties are involved in the overflow. The idea of using a detergent or glycerin surfactant to modify the surface tension would also change the dynamics of what is expelled.

There is a LOT of physics going on in this experiment in addition to the chemistry.