A powder made of sodium bicarbonate that is used as a leavening agent for making a variety of baked goods. It is activated as soon as it is mixed with liquid, such as water, and continues to react as it is added to a dough/batter mixture and warms to room temperature. This chemical reaction releases carbon dioxide gas that causes the baked item to rise. Baking soda is used in recipes that contain acidic ingredients, while baking powder is used as a means of adding acidic ingredients to recipes requiring it in order to make the dough rise. If properly stored in a cool dry area, baking soda can last for approximately 3 years. If stored in a warm or damp area, the soda begins to clump as the particles go through a chemical reaction, thus adversely affecting the flavor of baked goods using the soda. To determine if baking soda is still active, add a spoonful of the soda to a cup containing lemon juice or vinegar and see if it fizzes. Stale baking soda will be flat and will not fizz when combined with the vinegar or lemon juice.