Well, the obvious answer is "Baking soda is used in baking," but I'm pretty sure that isn't what you're looking for.
Another name for baking soda is "Sodium Bicarbonate" and it is used
in a lot of chemical reactions - baking soda is pretty easy to react
with other chemicals.
For fun, here's one that you can try at home:
Take about a tablespoon of baking soda, put it in a bowl, and add about a quarter cup of vinegar. Watch what happens.
If you want to try more with this reaction, try "Activity One"
a PDF reader)
Of course this is a lot of fun to do, but there are many more
reasons why people buy baking soda. Some people use it to clean up and
deodorize kitchens and bathrooms. One manufacturer of baking soda
recommends putting an open box in the fridge to remove odors. Some
people sprinkle it in cat litter to lessen the smell. Others use it in
toothpaste, and people add it to laundry detergent. Some people add it
to pool water to help it be more clear. The idea behind all of these
uses is mostly the same. Baking soda neutralizes acids, which are often
the causes of bad odors. Cat urine in particular is really stinky and
acidic, and so is vinegar. After the reaction with baking soda, the
salts that result are less noisome. One very popular use of baking soda
is to neutralize a portion of one's stomach acid. Having lots of extra
stomach acid can lead to damage in the esophagus as some of it is
regurgitated. Neutralizing it with baking soda helps relieve the pain
of heartburn (which really has nothing to do with the heart and
everything to do with acid coming back up from the stomach). Calcium
carbonate is a popular heartburn relief agent which works the same way,
and also supplies calcium, which is lacking in many people's diets,
while sodium is usually found in excess in people's diets. As with all
medications, please check the instructions on the box before ingesting
any. You may also burp (try the vinegar experiment above to see why).
(published on 10/22/2007)