Ask A Scientist© Chemistry Archive

name         Emily C.
status       student
age          11

Question -   My class did a science experiment that combined baking
soda and vinegar.  We put out a flame with the carbon dioxide gas.  My
teacher said that we made water, salt and carbon dioxide in the
reaction.  He said it was not table salt though.  When I asked what kind
it was he said I could get extra credit if I found out what kind of salt
it is.  Can you help me?  Thanks for your time!
------------------------
Your experiment was an example of a reaction between and acid (vinegar) and a
base (baking soda). Such reactions typically form a "salt" and water. In your
experiment, because the acid component was acetic acid, it allowed production
of one of the products ==> sodium acetate. That is the stuff referred to 
as the
"salt."

  In the general case of simple acid-base reactions, the term, "salt" 
 refers to
the non-water, ionic product. If hydrochloric acid and sodium hydroxide were
the reactants, then NaCl (common salt) would be the non-water product. Your
reaction looks like this:

HC2H3O2   +   NaHCO3  ===>   NaC2H3O2    +  H2CO3

Acetic acid plus sodium bicarbonate makes sodium acetate plus carbonic acid

The NaC2H3O2 is the salt called sodium acetate.

The H2CO3 (carbonic acid) then breaks down into water and carbon dioxide:

H2CO3  ===>   H2O   +   CO2

I hope this wins your extra credit

Regards,
ProfHoff
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Hello Emily :

          Since your teacher is offering to give you extra credit for
finding out which salt is formed, it wouldn't be fair for me to give you
the answer. However, I think that you can work this one out with a bit of
thought. Write down the chemical formulas for baking soda and for vinegar.
Then write down the chemical formulas for water and carbon dioxide. Since
no atoms are being created or distroyed in the reaction, whatever atoms
were added to the bottle with the flame, must still be there. Match up the
atoms contained in the water molecule and in the carbon dioxide with the
atoms contained in the baking soda and in the vinegar. Whichever atoms are
not accounted for must be the atoms forming the salt. Let me know how it went.

Jim Rubin
Los Alamos National Laboratory
=========================================================
I will not tell you the answer, but I will help you figure it out.  The active
component of vinegar is acetic acid, which donates a proton (H+) to the
sodium bicarbonate (baking soda).

H+ + NaHCO3 --> Na+ + H2CO3
H2CO3 --> H2O + CO2

What is missing in the equations I wrote?  Where is the rest of the acetic
acid?

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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