What is the difference between baking soda and baking powder? and where can you buy baking soda?

I was recently asked the above question by a friend in Uruguay, so here is the answer:

Both bicarbonate of soda (baking soda) and baking powder are leavening agents. When included in a batter, the leavening agent creates air bubbles that expand when cooked, and cause it to rise.

Bicarbonate of soda needs to be mixed with moisture and an acidic ingredient for the necessary chemical reaction to make it rise, such as lemon juice, chocolate, buttermilk or honey.  Baking powder often comes pre-mixed with the acidic ingredient for you – so all you need to do is add the moisture.

In Uruguay baking powder is readily available at any supermarket and it is normally the Royal brand.

Baking soda (bicarbonate of soda) however, can not be bought at the supermarket - it is bought over the counter at any pharmacy.  It also comes in very small bags and for those of us that bake a lot it pays to buy multiple bags at a time.  Also, if you like to clean with baking soda check this site out:  http://www.thenewhomemaker.com/cleanorg/soda.html