Bromothymol Blue and Respiration

Summary:

Students will compare how much carbon dioxide they breathe out before exercise and after. They will then create mini investigations to determine if other factors may influence the amount of CO2 produced by comparing person with asthma to a non-asthmatic, couch potato to an athlete. Students will breathe into a flask with the indicator, bromothymol blue (BTB), and then titrate it to the original color with weak sodium hydroxide (NaOH).

Learning Objectives:

Compare the amount of carbon dioxide in a person’s breath before and after exercise.

Investigate other factors that may influence how much carbon dioxide is exchanged in the lungs.

Graph and analyze the data.

Draw conclusions about factors that influence how much carbon dioxide is exchanged in the respiratory system based on data and observations.

Identify, plan and conduct other investigations that relate to this inquiry.

Relate the structures and functions of the respiratory system that are involved in the exchange of gases.

Appropriate for:

10th

11th

12th

Class Time:

one hour

Materials and Supplies:

Stock Bromothymol Blue (BTB) (Dilute .04% Bromothymol Blue Indicator Solution to .004%. When the flask is sitting on printed materials, you should be able to easily read the words through the pale blue solution. If the stock is greenish instead of blue, add weak NaOH to shift the solution to be more blue.) Each test group will need about 450 to 500 mls of diluted solution.

Per test group:

2 Erlenmeyer flasks (250 ml)

1 small beaker (100 ml)

3 to 5 straws per student who tests

Weak sodium hydroxide in a dropper bottle (.1 M NaOH)

Graduated cylinder (100 ml)

Timer or clock with a second hand

Safety eye wear

Background Information and Resources:

Students should not ingest the BTB and safety eye wear is recommended. See: MSDS http://www.flinnsci.com/Documents/MSDS/B/BrthyBIS.pdf

See student handout: BROMOTHMOL BLUE (BTB) and RESPIRATION for detailed description of the activity.

See: Lab Activity Checklist to evaluate how the teams collaborated and drew conclusions about the factors that influence carbon dioxide exchange in the respiratory system.

The color change is an indication of the amount of acid or base there is in the solution. The more dissolved carbon dioxide from the participant’s lungs, the more acidic it is. The faster it changes colors the more acidic it is. Carbon dioxide dissolves in the water to make carbonic acid (H20 + CO2 > H2CO3). The pH range for BTB is approximately 6.2 to 7.6. It is yellow when acidic and blue when basic. To see a color chart go to:

www.mysciencebox.org/files/bromthymol_blue.doc

The student will develop the abilities necessary to do scientific inquiry and develop an understanding of scientific inquiry.

Identify questions and concepts that guide scientific investigations

Design and conduct scientific investigations.

Use technology and mathematics to improve investigations and communications

Formulate and revise scientific explanations and models using logic and evidence

Communicate and defend a scientific argument

Use mathematics in all aspects of scientific inquiry.

The student will develop an understanding of the cell, molecular basis of heredity, biological evolution, interdependence of organisms, matter, energy, and organization in living systems, and the behavior of organisms.

Most cell functions involve chemical reactions

Cells can differentiate, and complex multicellular organisms are formed as a highly organized arrangement of differentiated cells.

Organisms have behavioral responses to internal changes and to external stimuli.

The student will develop an understanding of personal and community health.

Making a stock solution:

Most purchased solutions are 0.04% solutions. Dilute this solution so that the participants can read text through the bottom of the flask when it contains the diluted solution. (See materials section above.) Prepare enough stock to have each team to use about 500 mls of solution.
Students may need extra straws after exercising. Ask students to practice breathing in through their mouth and noses but only exhaling through the straws inserted in the solution. Caution them not to inhale or draw the solution into their mouths.