Re: Why does ice fizz when you put baking powder on it?

Are you sure you observe the ice fizzing?  If you look closely, you'll see 
the bubbles coming out of the solution of liquid water on the surface of 
the ice.  Two things are happening here.  
1.  If you add something that dissolves in water, like salt, sugar or 
baking powder to water, the melting point of the liquid water goes down.  
If you've ever seen homemade icecream being made, you'll notice that salt 
is added to the ice.  This melts part of the ice, but the rest of the ice 
and the salt/liquid water solution become much colder.  
2.  baking powder is a mixture of an acidulant (something that makes an 
acid), generally citric acid, tartaric acid, or both and baking soda, or 
sodium bicarbonate.  It's designed to produce carbon dioxide bubbles from 
the reaction of the bicarbonate with the acidulant.  Most baking powder 
sold these days is "double acting", because one of the acidulants reacts 
much slower than the other.  This allows an initial burst of carbon 
dioxide bubbles to be released in the cake batter as it is mixed initially 
and another release of carbon dioxide when the batter heats up in the oven 
so that the cake rises during the baking process.  

Try your experiment again.  Depending on the pH of your water supply I 
think you'll find that baking powder will fizz if you just get it wet.  
You can really make it fizz if you add a little vinegar to it.