Baking soda is sodium bicarbonate (NaHCO₃). When used in baking, it acts as a leavening agent. In the presence of heat or an acidic ingredient (like those often found in dough or baking powder), baking soda undergoes a chemical reaction that produces carbon dioxide (CO₂) gas. The main reactions are: 1. Decomposition by heat (slow without acid): 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g) 2. Reaction with an acid (e.g., citric acid, tartaric acid, or acids in buttermilk/yogurt): NaHCO₃(s) + H⁺(aq) → Na⁺(aq) + H₂O(l) + CO₂(g) The carbon dioxide gas gets trapped within the gluten matrix of the dough, causing it to expand and rise. This creates small air pockets, which give the bread or cake a light, fluffy, soft, and spongy texture.