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Lewis Acids and Bases

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Watch It Fizz

Watch It Fizz

          

Credit: Thavox
Source: https://commons.wikimedia.org/wiki/File:Sodium_bicarbonate.jpg
License: CC BY-NC 3.0

You and friends share a large pizza and watch a movie together. After they leave, you feel a burning in your stomach – acid indigestion. It’s too late to go to the store to buy some antacid tablets, so what do you do? Sodium bicarbonate to the rescue. Just mix about half a teaspoon of baking soda (note: this is not the same as baking powder) in a glass of water, drink, and you’re all set.

Why It Matters

  • Sodium bicarbonate is a seemingly simple molecule, but is actually rather complicated. The bicarbonate anion is a combination of the carbonate anion with proton which is attached to one of the oxygen atoms. The oxygen in this case serves as a Lewis base by donating a pair of electrons to the Lewis acid (the hydrogen ion which accepts the electron pair).
  • In water there is a complex equilibrium seen:
    • H2O + CO2 form the weak acid H2CO3 which is also in equilibrium with H+ + HCO3-.

LeChâtelier’s principle is in operation with this equilibrium. If the bicarbonate concentration is increased as you drink the sodium bicarb, the equilibrium shifts to the left, neutralizing the excess acid in your stomach. If enough carbon dioxide is formed, it will cause you to burp.

  • There are a number of over-the-counter products available for treatment of acid indigestion. Many of these contain either bicarbonate or carbonate salts (a carbonate anion can react with two hydrogen ions, whereas a bicarbonate anion will only react with one hydrogen ion). These antacids may contain cations other than sodium. Often, the specific metal cation can give rise to complications in certain groups of people. Calcium and aluminum-based antacids can cause constipation while antacids containing magnesium may produce diarrhea.
  • Credit: Shawn Campbell
    Source: http://www.flickr.com/photos/thecampbells/3367105978/
    License: CC BY-NC 3.0

    The variety of antacids available at a typical pharmacy [Figure2]

     

  • Baking soda has a multitude of applications around the home. In addition to its major contributions to cooking and relief of acid indigestion, sodium bicarbonate can also be used as an agent for cleaning the body and teeth. It has been used as a deodorant and a refreshing soak for the body or just for feet. This material can be very effective in cleaning dishes, pots and pans, and appliances. Your car can benefit from sodium bicarbonate to remove dirt and oils, while the solution will neutralize deposits that build up on the battery poles. A versatile material indeed.
  • Watch a video about acid indigestion at the link below: https://www.youtube.com/watch?v=JO074DchNqw

Can You Apply It?

Learn more about acid indigestion and its neutralization at the links below. Then answer the following questions.

  1. Why is sodium bicarbonate not recommended for individuals with high blood pressure, kidney disease, or heart problems?
  2. How do acid reducers work?
  3. How long should you normally take antacids?
  4. What does baking powder contain that is not found in baking soda?
  5. Why is baking soda useful in personal care?

Image Attributions

  1. [1]^ Credit: Thavox; Source: https://commons.wikimedia.org/wiki/File:Sodium_bicarbonate.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: Shawn Campbell; Source: http://www.flickr.com/photos/thecampbells/3367105978/; License: CC BY-NC 3.0

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