GO IN DEPTH

Acid Stomach

What You Need

Materials

  • Safety goggles
  • 9 plastic cups
  • Aspirin, Buffered Aspirin, Enteric Aspirin
  • 600 mL water
  • 300 mL vinegar
  • 45 g baking soda
  • Stop watch or a clock with a second hand
 
Acid Stomach

Purpose

To develop an understanding of how aspirin works and how understanding its interaction with other chemicals in the body aided doctors in medical research.


Context

This lesson is intended for a high-school, introductory chemistry class or health class. To complete the lesson, students must understand acids and bases. The lesson does provide for instruction in acids and bases if it is necessary. The lesson begins with an article on the history of the development of aspirin. Students will then complete a lab that compares the reaction of regular aspirin, buffered aspirin, and enteric aspirin in neutral, acidic, and basic solutions. They will then analyze the results of the experiment to gain insight into how this information was used by researchers to solve some of the problems associated with aspirin.


Motivation

Using the Acid Stomach student esheet, students should read The Aspirin Effect: Pain Relief and More from the American Chemical Society site. The article starts on page 3.

Discuss students' answers to these questions found on the esheet:

  • What do willow tree bark extract and aspirin have in common? (What these compounds have in common is their anti-inflammatory properties and they are some of the oldest and most frequently used drugs.)
  • The study of the chemistry of medicinal plants began in the 1800s. Why would it have been difficult to identify the active ingredients in those plants? (Chemical techniques of the day were relatively simple. In the bark of the willow tree, there would be hundreds of different compounds. Separating them from one another and identifying their effects in the body would have been very difficult with the limited knowledge and techniques.)
  • What were some of the drawbacks to salicylic acid as a pain reliever? (Salicylic acid is very irritating to the stomach. It can cause severe heartburn.)
  • Felix Hoffman, who worked for the Bayer Company, invented aspirin in 1897. How did he make it? (He acetylated salicylic acid, meaning that he replaced the hydrogen on the -OH groups with acetyl salicylic acid.)
  • What are some of the benefits of aspirin? (It relieves fever, pain, and inflammation, prevents some types of heart attacks, and inhibits clotting.)
  • How does aspirin work? (Aspirin stops the production of hormone-like compounds called prostaglandins. Aspirin interferes with the action on cyclooxygenase, which is the enzyme at the beginning of prostaglandin synthesis.)
  • What do you think are some possible strategies for reducing stomach irritation caused by aspirin? (These are not mentioned in the article, but try to lead your students to talking about buffered aspirin is a combination of aspirin with some other compounds to reduce acidity. Enteric aspirin is coated with a substance that allows the pill to pass through the stomach without being dissolved, thereby eliminating stomach irritation.)
  • What are some other medical discoveries that have been found as a result of our understanding of how aspirin works? (A specific prostaglandin that promotes coagulation of blood and another that inhibits it have been identified. A new group of prostaglandins that are related to the inflammation of asthma has also been discovered.)


Be sure that students save their answers to these questions because they will revisit them in the Assessment.


Development

Review acids/bases with your students. Depending on the level of the students, you could have them read: Acids and Bases as a review of acids/bases. This site is also very useful as a review for you if one is needed. You should use your discretion as how to best utilize this site.

After students have reviewed acids and bases, introduce the lab portion of the lesson by saying, "We will do an activity to better understand how buffered aspirins work."

Provide students with the Simulated Stomach Lab student sheet. Before they begin the lab, pass out the Simulated Stomach Lab Data Sheet and instruct them to record their observations in the data tables found there.

In doing this lab, students should find that when the three types of aspirin are dropped in water, the buffered aspirin may quickly begin to bubble and disintegrate. The enteric aspirin will eventually begin to disintegrate in the water, but it takes a very long time for the coating to dissolve and will not likely happen during a class period. In the acidic solution, the buffered aspirin very quickly begins to bubble vigorously. The regular aspirin disintegrates in the acidic solution just the way it does in water. The enteric aspirin can soak in the acidic solution for several hours without dissolving. In the basic solution (baking soda), all three types of aspirin will dissolve relatively quickly, although the enteric aspirin still takes longer than the other two. (In these solutions, vigorous bubbling—probably more than seen in any case previously—should be seen in all cases as the acidic proton on aspirin reacts with the bicarbonate ion to produce carbonic acid, which breaks down to carbon dioxide gas and water.)


Assessment

Have students answer these questions either online or on the printable student sheet, Understanding What You Learned. The first four questions are repeats of some of the questions found in the Motivation.

  • What were some of the drawbacks to salicylic acid as a pain reliever? (Salicylic acid is very irritating to the stomach. It can cause severe heartburn.)
  • What are some of the benefits of aspirin? (It relieves fever, pain, and inflammation, prevents some types of heart attacks, and inhibits clotting.)
  • How does aspirin work? (Aspirin stops the production of hormone-like compounds called prostaglandins. Aspirin interferes with the action of cyclooxygenase, which is the enzyme at the beginning of prostaglandin synthesis.)
  • What are some strategies for reducing stomach irritation caused by aspirin? (Buffered aspirin is a combination of aspirin with some other compounds to reduce acidity. Enteric aspirin is coated with a substance that allows the pill to pass through the stomach without being dissolved, thereby eliminating stomach irritation.)
  • How would knowledge of the way aspirin reacts in acidic, basic, and neutral (water) solutions help in solving the problem of stomach irritation? (The stomach is an acidic environment. Knowing how aspirin reacts in an acid helped doctors find ways to reduce the acidity [Buffered Aspirin]. It also helped them to devise a way for the aspirin to not react at all in the stomach [Enteric Aspirin].)
  • How has the understanding of aspirin's molecular structure and its interaction with other chemicals in the body aided doctors in medical research? (Investigation of aspirin interactions led to a better understanding of the varied roles of prostaglandins. Prostaglandins are the cause of some types of inflammation.)
  • What differences, if any, did you observe in the tablets while in water? In vinegar? In baking soda solution? (See description of lab above.)
  • Enteric aspirin is designed to remain intact until it reaches the small intestine. What could you hypothesize about the pH of the small intestine? (Because enteric aspirin does not react in the acid, but very quickly dissolves in the basic solution, we might hypothesize that the pH in the small intestine is basic.)

Extensions

These sites can be used to extend the ideas and concepts in this lesson:


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Lesson Details

Grades Themes Type Project 2061 Benchmarks
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