Chapter 6 Ions: Charged Particles in Solution 105 The equation below shows what happens when baking soda and vinegar (5% solution of acetic acid) are combined. NaHCO3 + CH3COOH Na(CH3COO) + H2O + CO2 sodium bicarbonate + acetic acid sodium acetate + water + carbon dioxide Baking soda will leaven a product if acid is not present. However, the by-product, sodium carbonate, has a bitter flavor. The product will also have a yellowish color. Heat must be added for this reaction to occur. heat 2NaHCO3 CO2 + Na2CO3 + H2O sodium carbon + sodium + water bicarbonate dioxide carbonate Baking Powder Baking powder is a combination of baking soda, dry acids, and a filler. Most baking powders used in the United States have two dry acids. One acid reacts when exposed to moisture and the other acid reacts when heated. These baking powders are called double-acting baking powders. The filler in baking powder absorbs moisture to help prevent the baking soda and acids from reacting prematurely. The most common fillers are cornstarch and calcium carbonate. Cream of tartar (potassium bitartrate) is one of the moisture-activated dry acids often used in baking powders. When liquid is added, the cream of tartar begins a two-step reaction with the baking soda. This reaction results in the release of some carbon dioxide before baking begins. If batter or dough is overmixed or baking is delayed, this carbon dioxide can be worked out of the mixture. Therefore, it is important to quickly finish mixing and begin the baking process after adding baking powder to a mixture. The formula below shows the first step in the two-step reaction between the baking soda and cream of tartar. moisure NaHCO3 + KHC4H4O6 KNaC4H4O6 + H2CO3 sodium + potassium sodium potassium + carbonic bicarbonate bitartrate tartrate acid (baking powder) The following formula shows the second step in the two-step reaction between the baking soda and cream of tartar. H2CO3 H2O + CO2 carbonic acid water + carbon dioxide In double-acting baking powder, most of the carbon dioxide is released after the product is exposed to heat. Several dry acids react slowly or only after heat is added. These include calcium dihydrogen phosphate, sodium aluminum sulfate, and sodium dihydrogen pyrophosphate. Most commercial baking powders are made with sodium dihydrogen pyrophosphate. These baking powders release about 30% to 40% of the carbon dioxide during mixing. They release another 10% if the product is allowed to stand more than 15 minutes. They release the remaining 50% to 60% during baking. These baking powders produce sodium pyrophosphate as a by-product. This substance does not give a bitter flavor to the finished product like the sodium carbonate produced by baking soda. See 6-13. heat NaHCO3 + Na2H2P2O7 Na3HP2O7 + CO2 + H2O sodium + sodium dihydrogen sodium + carbon water bicarbonate pyrophosphate pyrophosphate dioxide In each of the chemical leavening agents discussed so far, the gas that is produced is carbon dioxide. This is the only gas produced by chemical leavening agents available for retail sale in the United States. By law, baking powder must release 12 g of carbon dioxide per 100 g of baking powder. Ammonium Bicarbonate Ammonium bicarbonate is a chemical leavening agent that does not form a solid product that remains in the dough. However, the ammonia gas that is produced can affect the taste of the product if it ozgurkeser/iStock/Getty Images Plus 6-13 Baking soda must be used with an acid ingredient like vinegar or lemon juice. Baking powder contains a dry acid and needs only the addition of water and heat. Copyright Goodheart-Willcox Co., Inc.