Do you ever wonder if that box of baking soda is still active? Before replacing it, pour a little bit of white vinegar in a bowl and add 1 tablespoon of it to it. If it bubbles and fizzes right away it’s good. If you get no reaction, it’s time to toss! Why? It means there is no gas left in it which will leave your baked goods flat. Baking soda is a leavening agent that relies on chemical reactions to produce carbon dioxide gas (the bubbles).