By Harold McGee
The most common alkaline component of chemical leavenings is sodium bicarbonate (or sodium acid carbonate, NaHCO3), usually called baking soda.
Baking soda can be the sole added leavening if the dough or batter contains acids to react with it. Common acid ingredients include sourdough cultures, fermented milks (buttermilk, yogurt), brown sugar and molasses, chocolate, and cocoa (if not dutched), as well as fruit juices and vinegar. A general rule of thumb: ½ teaspoon/2 gm baking soda is neutralized by 1 cup/240 ml of fermented milk, or 1 teaspoon/5ml of lemon juice or vinegar, or 1¼ teaspoons/5 gm cream of tartar.