There She Blows!

So this is another entry from our Rainy Day Science Demo.  This is a classic one…the old vinegar meets baking soda reaction that is the centerpiece of every volcano project in elementary school.  To make it a little more interesting, we decided to forego the volcano aspect (well maybe “more interesting” is not the right phrase) and use a balloon to trap the gas created by the reaction.  Some shots from the scene…

The Analyst adding some vinegar to our water bottle.

Putting baking soda into a balloon using our homemade funnel - by far the trickiest part of the demo; the baking soda kept clogging up in the funnel.

The Actress placing the balloon over the top of the bottle as The Analyst blows up balloons in the background. Trying to teach a science lesson here and the package of balloons was the highlight of the event!

Tip the balloon so the baking soda dumps into the vinegar and what do you get? A blown up balloon of course!

So after the initial demonstration we attempted to turn it into a simple experiment.  I posed the question: “What do you think will happen if we have more baking soda in the balloon?”  The answer out of my little budding scientists…”It will blow up more!”  The beginning of their first hypothesis!

4T of baking soda instead of 2!

It certainly blew up more. In fact it blew the balloon off and splattered acetic acid onto the ceiling (found a week later)!

The Science Behind It…

So what is going on here anyway?  Well this “reaction” is actually two reactions that happen in quick succession.  To start with, vinegar is acetic acid (CH₃COOH) and baking soda is sodium bicarbonate (NaHCO₃).  What happens when they mix is a simple double replacement (AX + BY –> AY + BX) acid-base reaction:

CH3COOH(aq) + NaHCO3(s) —> CH3COONa(aq) + H2CO3

The sodium and hydrogen ions essentially “switch places” (.  The sodium replaces the H in the acetic acid to form sodium acetate.  Simultaneously the displaced hydrogen ion replaces the sodium to form carbonic acid.  Carbonic acid is a weak acid that quickly undergoes a decomposition reaction (AB –> A + B) to form carbon dioxide and water:

H2CO3 –> H2O(l) + CO2(g)

What you are seeing filling up the balloon then is the CO2 gas that has escaped from solution.