Small Research Projects in the Chemistry Classroom

You may have read Sarah Kong's recent blog post on inquiry on this site. I thought I would give a description of one way I incorporate inquiry learning into one of the chemistry courses I teach. 

As part of the course requirements for General Chemistry II at Spring Arbor University (where I teach), students are required to complete a small research project.  I have included this research component in General Chemistry II for 8 years now.  Students work on this project during the final four laboratory periods of the semester.  The research projects are conducted at the end of the academic year in order to ensure that students have acquired the necessary skills (from both lab and lecture) to successfully complete the work. 

Students conduct experiments during three of the final four lab periods, and present their results at a poster session held during the final laboratory session.  Before the laboratory experiments begin, each student meets with me to choose a reasonable project (one the student can probably finish in three, 3-hour lab periods).  Each student and I try to find a topic that interests the student.  In addition, I work to assign projects that are open-ended:  the student does not know what is going to happen during the proposed experiment.  I suppose this is just another way of saying I try to build inquiry learning into each proposed experiment.  I am not always successful in these regards (finding a project of interest for the student, or building inquiry into the project).

On average, 50 students take General Chemistry II each spring semester at Spring Arbor, with about 17 students in 4 lab sections.  That’s a lot of different experiments!  Obviously, designing and completing all these projects each year has been (and continues to be) challenging.  It is helpful to have students repeat experiments done in previous years.  Also, repeating previous experiments with slight modifications keeps things interesting for me.  Despite the many challenges I face with these assignments, having students work on small projects like this is perhaps my favorite part of teaching chemistry.  My students and I really get in to it, and we both learn so much!  It is not uncommon for students to go well above and beyond the call of duty to work on their projects (I had one student a few years ago work over 40 hours on a project).  Some students have even decided to keep working on their project after they have completed my class. 

The vast majority of the time, I assign projects that can be completed with simple materials.  Below I will describe one such experiment, and I hope to share more in the future.  I also hope that you will take the time to share some ideas with me.  I am always looking for new experiments to have students try! 

I’ll first describe an experiment done by a student interested in physiology.  He and I decided to use what we know about gas pressure to measure the pressure inside our lungs upon inhalation.  We knew that a column of a liquid can be supported to a height, h, by air pressure (Figure 1).

Figure 1:  A column of liquid with height, h, supported by air pressure

The air pressure (P_ATM) exerts a pressure equal to the pressure of the liquid in the tube (P_Liquid).  If there is a vacuum in the tube, then we have:

P_ATM = P_Liquid    Equation 1

Because P_Liquid = Dgh, where D is the density of the liquid in the tube in kg m^-3, g = 9.8 ms^-2 and h is the height of the liquid column supported by the atmosphere, we can write:

P_ATM = Dgh       Equation 2

 We always used water for our liquid, so D = 1000 kg m^-3.  It should be noted that P_ATM in the above equation will have units of Pa, or Nm^-2 (1 atm = 101325 Pa).

Now let’s imagine the same scenario being set up by a person sucking through a straw (Figure 2).  In this case, there is not a perfect vacuum at the top of the tube (according to our measurements, humans are incapable of making a perfect vacuum in their lungs). 

Figure 2:  A column of liquid being supported by someone sucking through a straw

In this case, we still have the atmospheric pressure being equal to the pressure inside the tube, or straw.  However, because there is no longer a vacuum at the top of the tube, we have:

P_ATM = P_Liquid + P_Lungs    Equation 3

Since we know the pressure of the liquid, we can write:

P_ATM = Dgh + P_Lungs       Equation 4

 Rearranging, we get:

P_Lungs = P_ATM – Dgh       Equation 5

The above equation gives us a way to measure the pressure inside lungs upon inhalation.  We get a REALLY long straw, and have someone suck water up the straw as high as possible.  Let’s suppose someone is able to suck water up a straw to a height of 6.42 m when the atmospheric pressure is 735 mm Hg.  What would have been the pressure in the person’s lungs?

We substitute the appropriate values in to Equation 5:

 We convert 735 mmHg to Pa:

 We now calculate the pressure of the liquid, by evaluating the second term on the right hand side of the above equation:

 We substitute this result in for the pressure of the liquid to find the pressure in the lungs in Pa:

We convert this result to atmospheres and mmHg:

So that’s the idea for the experiment.  Now all we had to do was find a really long straw, put it in some water and see how high we could suck the water up the straw!

 Here’s what my student (I’ll call him John) did:  He decided to take a very long piece of rubber tubing and place it in a 2L soda bottle filled with water (Figure 3):

Figure 3: The end of a 30 ft rubber tube placed in a 2L bottled filled with water (colored with food dye).

 He placed the 2L soda bottle at the bottom of a stair well (Figure 4).

Figure 4:  Picture from the top floor of a 3-story building, looking down the stair well at the 2L bottle and rubber tubing.

 He then had people suck water through the tubing as high as they possibly could:  the higher the person could suck the water up the tube, the lower the pressure formed in the lungs.  (Note:  we used scissors to cut off the end of the tube after each person tried the experiment to avoid sharing germs).  John was able to pull a pressure of about 300 mmHg; I was able to get 225 mmHg.  He brought his apparatus back to his second story dorm room and repeated the experiment, measuring the lowest pressure some of his dorm mates could produce in their lungs.  He saw a lot of variability; the highest pressure measured was over 530 mmHg, while the lowest lung pressure was 188 mmHg. 

 I know this experiment seems incredibly simple, and that John could have easily completed it in a single, 3-hour period if I told him everything to do.  But I let John figure a lot out on his own.  He came up with the experimental procedure on his own.  John had a lot of trouble with the calculations, and I helped him quite a bit with these.  Because there are lots of students in each lab section, they find out very quickly that I can’t possibly help everyone every time they have a question.  I provide assistance when questions arise, and step in when I see a student that is seriously stuck.  But the students work out many problems on their own, and spend a lot of time talking with each other about possible solutions. 

 Because I have a lot of students interested in biology, I am thinking of repeating this experiment this spring.  The interested student will measure the lung pressure pulled by a variety of people and see if it can be related to some physical measurement.  For example, can men pull lower vacuum than women?  Is ability to pull a low lung pressure related to physical fitness?  Do sprinters or distance runners have a better ability to pull a low pressure than the general population?  Is height related?  There are many interesting questions to explore!  I’d love to hear about anything you and your students discover when trying this experiment. 

Also, some experiments we have done suggest that the diameter of the tube used affects the results.  People seem to be able to suck the liquid higher up tubes with smaller diameters.  We currently don't have a good explanation for why this might be so. 

 For other interesting ways to use pressure experiments in the classroom, see:  Sandy Van Natta , Rebecca Knipp , John P. Williams  J. Chem. Educ., 2005, 82 (10), p 1454