Sodium bicarbonate

Sodium bicarbonate (NaHCO3), also known as baking soda or sodium hydrogen carbonate, is a white powder that readily dissolves in water to produce sodium (Na+) ions and bicarbonate (HCO3) ions. In the presence of acids, these ions create carbon dioxide gas (CO2) and water. Baking soda, a weak base, is used in antacids, fire extinguishers, and baking powder. In almost all of its common uses, sodium bicarbonate is employed to produce carbon dioxide gas.

Use in antacids

Many commercial preparations of antacids contain sodium bicarbonate. Alka-Seltzer antacid contains sodium bicarbonate in addition to citric acid (C6H8O7), which is used to dissolve the sodium bicarbonate. Pure baking soda will also relieve heartburn, but the citric acid in commercial antacids improves the taste and accelerates the disintegration of the tablet. When sodium bicarbonate is dissolved in water, the compound separates into ions, or charged particles, of sodium (Na+) and bicarbonate (HCO3). The bicarbonate ions then react with acids as shown below. The symbol (aq), meaning aqueous, shows that the substance is dissolved in water; the symbol (g) refers to a gas, and (l) means a liquid. The hydrogen ions (H+) are from acids.

As shown above, one hydrogen ion and one bicarbonate ion react to produce a molecule of water and a molecule of carbon dioxide gas. This can be demonstrated at home by filling a reclosable plastic bag with one ounce (30 ml) of vinegar. The vinegar represents stomach acid. A teaspoon (5 ml) of baking soda (or an Alka-Seltzer tablet) is then dropped in the bag and the bag is quickly closed. The fizzing is caused by the production of carbon dioxide gas. The bag will quickly fill up with gas, demonstrating why many people burp after taking an antacid. This belching helps relieve the pressure that builds up in the stomach. In spite of its widespread use, sodium bicarbonate can be harmful in large doses by disrupting the levels of sodium ions in the bloodstream. In a few rare cases, some people have consumed such large amounts of sodium bicarbonate that their stomachs were damaged by the internal pressure that built up from the carbon dioxide gas.

Use in fighting fires

When sodium bicarbonate is heated above 518°F (270°C) it decomposes and produces carbon dioxide. Since carbon dioxide gas is more dense than air, it tends to sink; thus carbon dioxide can smother a fire by obstructing the flow of oxygen to the fuel, which needs oxygen to continue burning. Sodium bicarbonate is employed in fire extinguishers and is widely used on electrical fires.

Use in baking

Baking powder consists of sodium bicarbonate mixed with a weak acid. In much the same manner as citric acid produces carbon dioxide gas in some antacids, the weak acid in baking powder—often potassium hydrogen tartrate (KHC4H4O6)—provides a source of hydrogen ions; the ions react with the sodium bicarbonate to produce carbon dioxide gas, which makes dough and batter rise. Baking powder is often used as a source of carbon dioxide in baking instead of yeast , since yeast produces a distinct taste that is not desirable in all foods, such as cakes.

See also Acids and bases.

Resources

books

Francis, Frederick. Wiley Encyclopedia of Food Science and Technology. New York: Wiley, 1999.

Lewis, Richard L. Food Additives Handbook. New York: Van Nostrand Reinhold, 1989.

Snyder, C.H. The Extraordinary Chemistry of Ordinary Things. 4th ed. New York: John Wiley and Sons, 2002.

periodicals

Campbell, Hannah. "The Baker's Friend: How America's Best Brand of Baking Soda Was Born." Country Living vol. 12, March 1989.

Norton, Clark. "Facts on Fizz; Bubbly or Creamy, Calcium or Aluminum? Here's How to Choose a Heartburn Remedy." Health vol. 5, July/August 1991.

"Stomach Acid-An Old Remedy." Consumer Reports vol. 59, February 1994.

Louis Gotlib

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Antacid

—A basic (alkaline) chemical that relieves the effects of excess stomach acids.

Aqueous

—A solution dissolved in water; salt water could be called aqueous salt.

Ion

—An atom or molecule which has acquired electrical charge by either losing electrons (positively charged ion) or gaining electrons (negatively charged ion).