Expert: Amy - 1/25/2005

Question
My daughter 8th grade is doing sci fair proj:
Wine bottle filled with solutions of vinegar and baking soda (varying proportions for her data table)cork applied, lay it on its side and wait for gas to build up, shooting cork a measurable distance in a measurable amt of time. She hypothesises that if you use a certain propotion and double it, cork will go twice as far. What equations do we use to calculate the pressure built up inside bottle?   Thanks! Desperate Mom  

Answer
Hi Debbie,
I'd like to say first and foremost that my background is chemistry so I can only tell you part of what's happening inside the bottle from my own knowldege. However, I've spoken to someone else with more knowledge in the field and this is what we've come up with.

For starters, what's happening in the bottle is really really complicated and depends on a million of different variables. The exact concentration of vinegar, how dry the bicarb is when you start, the temperature, + a number of other things all play a role. The actual chemical reaction itself is quite complicated as well.

HC2H3O2(aq) + NaHCO3(aq)  NaC2H3O2(aq) + H2O( ) + CO2(g)

The build up of the carbon dioxide gas is what causes the cork to shoot out.

So.....the best way to look at it is to create your own equation from what you observe. A lot of science starts out that way.

Set up an experiment where you test a range of different amounts of vinegar and baking soda. Preferably, do it all in one day (to get similar temperature with all of the experiments) and make sure the bottle is cleaned out thoroughly and dried properly in between. Do each experiment 3 times to make sure you're getting some kind of consistancy.

Having the bottle on the table is a good idea cause the bottle is at the same angle each time. sure that there's no wind. Note down what angle you have the bottle.

When you've done all of these things, write back with all of your data and we'll see what we can come up with together. I'm away from my computer for the next few days though, so I won't be able to reply straight away.

I also suggest that you find someone with a physics background on this site. They'll have other things to add.

I hope this helps,

Amy