Over-the-Counter Pharmaceuticals

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Students will explore how over-the-counter drugs have different properties and identify an unknown pharmaceutical through performing a laboratory.

Big Idea

Over-the-counter drugs are used to relieve symptoms based on their properties.


In this lesson students have the opportunity to act as Forensic Chemists by performing a lab with common over-the-counter pharmaceuticals.  This lesson comes from the Health and Science Pipeline initiative's (HASPI) Medical Chemistry Curriculum with some revisions.  All of HASPI's lessons can be found on their website.  I have found that theses lessons are a great resource to bring real-world applications to chemistry class.  Through doing this students become more engaged in the lesson and better understand the importance of learning chemistry.

  • This lesson aligns with NGSS Science and Engineering Practice 3: Planning and Carrying out Investigations because students are performing a lab.
  • This lesson also aligns with NGSS Science and Engineering Practices 4: Analyzing and Interpreting Data because students are analyzing the data from their lab to better understand the results of their tests and to identify an unknown drug.
  • This lesson also aligns with NGSS Cross Cutting Concept 1: Patterns.  It does so because students take the data from the first four tests to determine the identity of the unknown pharmaceutical.

There are several materials needed for the lab including:

  • One tablet per group of Tums, Alka-Seltzer, Tylenol, and Aspirin.
  • Unlabeled vials for unknown including Tums, Alka-Seltzer, Tylenol, and Aspirin.  This picture shows the unknown vials.
  • One bucket per group containing 3 pre-labeled 12-well spot plates, universal indicator, distilled water, lots of toothpicks, mineral oil, 50% ethanol, mortar and pestle, scoopula, iodine solution, iron (III) nitrate solution, pH paper, indicator chart, and paper with the drug labels.   This picture shows the lab set up.
  • Conductivity testers at a separate lab station with each of the four drugs dissolved in water. This picture shows how I set up the conductivity station.
  • For some lab hints see the reflection on lab set-up.


5 minutes

To introduce students to the lesson I have them answer two prelab questions. 

  1. When you have a headache, cold, the flu, or an injury, or irritating heartburn, what determines which medicine you will take to relieve your painful, unwanted symptoms?
  2. How do you know if the medicine will work for your illness?

These questions are found on the top of the first page of the lab

I give students some time to think on their own first and then have them discuss with their groups. 

I then call on the different groups to discuss the questions.  This video shows how I discuss this with my students.  Rather than calling on students individually, I will often call on students by group and then one student in the group will share out.  I find this especially helpful when I give students time to discuss in groups.  It is difficult to hear the students in this clip, but I repeat what they say for the rest of the class to hear.


5 minutes

In this portion of the lab I go over the basics of the lab.

This includes the following:

1. I tell students that they will be performing tests on four known substances and then use their data to determine the identity of an unknown substances.  These tests include...

  • solubility in water
  • solubility in ethanol
  • solubility in oil
  • determining pH
  • reaction with an acid
  • reaction with iron III nitrate
  • reaction with iodine
  • conductivity

2. I also point out to them that they will be going to the conductivity station to determine the conductivity of the four known drugs and that they will not find the conductivity of the unknown.

3. I also let them know that they will not get the unknown substance until they are done with testing the first four.

I then break students up into cooperative lab groups.  This picture shows the groups and how I have them rotate. I remind them that they should be switching roles throughout the lab.  For more information about collaborative lab groups see my reflection from unit 1.


60 minutes

In this section students are actually doing the lab on their Lab Paper

As students perform the lab I walk around and make sure that students are staying on task and all participating.  I also look at their observations to make sure that they are recording appropriate information for the tests.  Some of the most common issues students have include:

  1. Not using the toothpicks to stir for each test.  As I walk around I encourage students to stir so they can better determine the results of the tests.
  2. Not recording physical appearance and odor.  I address some of this with changes to the procedure to have them note physical appearance and odor while grinding the drug. 
  3. Not understanding what to write for solubility in tests 1-3.  I prompt students to look back at the test instructions where it explains how to determine solubility based on how well the substance dissolves.  Despite this, many students still have a hart time determining between soluble, slightly soluble, and insoluble.  The goal is to begin to have students thinking about these terms, so if they get varied results it does not matter.
  4. For the pH test (test 4) some students need help with comparing colors of the universal indicator to determine pH levels.  I encourage students to write down the color they see and then estimate what that pH would be from the indicator chart. 
  5. Similarly with test 5 some students need help with using pH paper where I also encourage them to write down the color/numbers as well as if they see a reaction occurring.

This picture shows the results of one group's tests.  The amount of different colors in each of the wells gets students really excited about the lab. 

This pdf is an answer key with the 3rd page containing the expected results for each of the well plates.


15 minutes

In this section students answer questions at the end of their Lab Paper to analyze their results.  I encourage students to brainstorm answers together, but that they should write answers in their own words.

The 3rd and 4th pages of this pdf contain expected answers from students.


This is one of the few labs that I grade without a rubric.  I basically give students points for having completed data and then for answering the questions. 

This is a copy of a graded lab.  Notice that the lab is worth 25 points total.  Each of the questions is worth 1 or 2 points and the table is worth 11 points, 1 point for each row.  If students are missing parts of the table I deduct .25 points for each missing box up to 11.    

This particular student did well with answering the questions and only missed question number 6, "Why would the results from test #5 make a difference when you take over-the-counter drugs?"

- I was expecting an answer of how the drug may change the acidity of your stomach.

The other question that a lot of students struggled with was question number 3, "Why would solubility matter when taking a drug?" 

- This student gave an answer that I was hoping for which was, "It matters because if the drug is insoluble then it won't dissolve when it is inside the body."