Research Question

How does exercise affect the average person's carbon dioxide (CO²)  output?

Hypothesis

If a person exercises, then their carbon dioxide output will increase, because the heart has to pump excess amounts of blood that saturates oxygen, which spreads around the body faster than normal. This is due to the body needing extra oxygen, for the muscles, ligaments and other body parts to function under stress. The blood returns to the lungs in a deoxygenated state, with the blood containing carbon dioxide which, through respiration, exits the body.

 

What is respiration?

• To put it simply, respiration is another term to describe breathing.
• In the process of respiration, we are moving gases in and out of our lungs.
• Specifically, respiration is inhaling oxygen (O²) from the air around us, and thus expelling any unwanted carbon dioxide (CO²) content from our lungs.
• In totality, the formula used for cellular respiration is C₆H₁₂O_{2 +} 6O₂  →  6CO₂ + 6H2O + Energy(no chemical formula)
  • This stands for how Glucose(sugar) and Oxygen turns in to Carbon Dioxide(which is expelled from our body) alongside Water and Energy for our body as well.

How do respiration and blood circulation relate?

• When a person breathes in, the oxygen in the air travels through the larynx, trachea and bronchi to the lungs.
• In order for the oxygen to reach organs, it travels via the bloodstream.
• The lungs and heart work together to exchange oxygen and carbon dioxide in the lungs from the blood. This process is called gas exchange.
• After deoxygenated blood exits the heart through the pulmonary artery, it travels to the lungs to get oxygen. 
• After oxygen is replenished, it saturates the blood, and the blood enters the heart through the pulmonary vein.
• Blood oxygen saturation is measured as Sp02%, with a level of 95-100% being ideal. This can indicate breathing rate as well.
• The oxygenated blood then travels away from the heart through the arteries, and returns to the heart in a deoxygenated state through the veins.
• The process then repeats. If breathing rate is higher, the process happens faster in order to provide ample oxygen amounts to all parts of the body. 
• Information like Sp02%, breaths per minute, and heart rate can determine if a person is breathing and if their body's functioning correctly.

What does pH mean?

• The term pH is a term used in chemistry which stands for "The potential of hydrogen".
• In more chemistry aligned terms, it is primarily determined by the amount of hydrogen ions in a substance, alongside various other factors.
• pH = -log[H+] is the formula used to determine pH. It is the negative logarithm of the concentration of hydrogen ions in a substance (Base 10).
• It's a numerical way of measuring how basic/alkaline or acidic a substance is.
• pH indicators such as bromothymol blue, which we used in our respirators are generally considered as weak acids and bases
  • The reason they change colour over certain ranges of pH is due to the fact that their chemical structure causes changes in the absorption and reflection of different wavelengths of light as hydrogen ions, which are essentialy protons, are added to these.
  • When these hydrogen ions/protons are added to the indicator solution, it increases this solution's acidity as a result. Thus, the higher concentration of these, the more acidic the substance
  • For example, bromothymol blue changes colour when its acidity increases, from blue to teal to green to yellow. This will prove important later on in our experiment.
• In this experiment, we used a colorimetric pH test which changed in colour depending on how acidic or basic the solution was.
• Generally, the more acidic a solution, the lower the number associated with it, and the more basic, the higher number associated with it. A pH level of 7 is considered neutral and is associated with pure water.
• As we're measuring carbon dioxide output in this experiment, we're going to be checking how acidic the water is after respiration, due to carbon dioxide being an acidic gas.

Manipulated (Independent) Variable: Whether the tested person(s) exercises or not prior to breathing into the respirator.

 

Responding (Dependent) Variable: Amount of carbon dioxide (CO²) output by the tested person before and after they exercise. We also analyze the possible implications of lower breathing and heart rates, as well as factors that can cause this.

 

Controlled Variables (5): Same location, Same person (for each set of trials), Same amount of time breathing into the respirator for each trial (15 seconds, 1st experiment only), Same amount of time exercising ahead of respiration (1 minute per trial), Same type of pH strips used throughout. 

 

Materials

To build the respirators

• 2 plastic water bottles
• Tap water (167 ml per bottle)
• Scissors
• Aerator Setup
• Safety Valve

To do the experiment

• Bromothymol blue solution (5ml in total per respirator)
• Lab partner- to record info
• Stopwatch
• PH strips
• Watches with heart rate monitoring (different watches with each person.)

Procedures

The first experiment's procedure

1. Create our respirator (link used in bibliography for ideas, actual respirator in images)
2. Place 5 ml of the bromothymol blue solution into 167 ml of tap water.
3. The first tested person will breathe into the respirator without having done exercise, and their lab partner will check the color of the water 60 seconds after the tested person finishes breathing, and after 60 seconds they will check the PH levels of the water using PH strips.
4. Then, the lab partner will aerate the water using the oxygen aerator setup, sending it back to its original state 
5. Repeat steps 3–4 three times, and record the results of each trial
6. After trial #3, make the tested person complete any form of aerobic exercise(push ups, jumping jacks, etc) for 1 minute
7. Then, repeat steps 3-4 again, ensuring that the tested person completes exercise ahead of breathing into the respirator, while still recording the results of each trial.

• We will also be checking the person’s heart rate before and after they exercise to see how heart rate affects their carbon dioxide output.

8. Using the PH levels from the 3 trials the tested person did without exercising, and the 3 they did after exercising, we will determine the difference in CO₂ output. 

The second experiment's procedure

To understand the true effect of exercise on the output of carbon dioxide, what we measured in this experiment was modified to identify the time it takes to change the water colour between resting and exercise trials, per the procedure below:

1. Place 5 ml of the bromothymol blue solution into 167 ml of tap water, and 5ml in the 167 ml of distilled water.
2. The first tested person will breathe into the respirator with the tap water in it without having done exercise, and their lab partner will wait until they change its colour from teal to green. Then, they'll track how long the person had to breathe in the respirator to do this.
3. Then, the tested person will breathe into the respirator with the distilled water in it, and their lab partner will wait until they change the water colour from pale to golden yellow. Then, they’ll track how long it took for them to do this
4. After they breathed into both respirators, the lab partner will aerate both respirators, back to their original states.
5. Repeat steps 3-5 two more times to end up with 3 trials in total.
6. Then, complete steps 3-5 three more times, this time ensuring that the tested person exercises for 1 minute before breathing into the respirator this time.
7. Now, compare your results from the trials with and without exercise. The shorter it took to change the colour of the water, the more CO2 was outputted by the person.

Below is some data and observations from our first experiment

Bromothymol blue (raw solution) initial pH level

pH = 7-ish. The pH strips we used only gave approximations for each level so we were unable to find out the exact decimal point pH level. The pH strips dried out quickly so later on they gave the illusion that the level was 6. Due to the strips not giving a precise and decimal-point result, we only have an approximate reading.

We discovered that bromothymol works best in fluids with 6.0 to 7.6 pH, and it’s commonly used in fluids with a pH level of approximately 7. The colour also changes depending on that pH level. Bromothymol blue turns yellow in solutions with pH < 6.5, green/teal between 6.5 - 7.2 and blue at pH > 7.2.

Underneath are tables of data gained in our first experiment

                                                                                          Navneeth(resting)

Trial #	Duration of Respiration	Heart Rate immediately after resting period (bpm)	Water colour 1 minute after respiration	pH level 1 minute after respiration
1	15 sec	98	teal	6
2	15 sec	88	light greenish teal	8
3	15 sec	83	green	7

 

                                                                                            Shreyas(resting)

Trial #	Duration of Respiration	Heart Rate immediately after resting period (bpm)	Water colour 1 minute after respiration	pH level 1 minute after respiration
1	15 sec	78	dark teal	7
2	15 sec	67	dark teal	7
3	15 sec	66	dark greenish teal	7

 

                                                                                    Navneeth(exercise)

Trial #	Type of exercise completed	Duration of Respiration	Heart Rate immediately after resting period (bpm)	Water colour 1 minute after respiration	pH level 1 minute after respiration
1	Jumping Jacks	15 seconds	131	green	7
2	Jumping Jacks	15 seconds	136	green	7
3	Jumping Jacks	15 seconds	161	green	7

 

                                                                                          Shreyas(exercise)

Trial #	Type of exercise completed	Duration of Respiration	Heart Rate immediately after resting period (bpm)	Water colour 1 minute after respiration	pH level 1 minute after respiration
1	Jumping Jacks	15 seconds	130	teal	7
2	Jumping Jacks	15 seconds	136	teal	7
3	Jumping Jacks	15 seconds	135	green	7

 

pH Averages

Navneeth (without exercise) - 7.3

Shreyas (without exercise) - 7

Navneeth (with exercise) - 7

Shreyas (with exercise) - 7

 

We noticed that overall the pH level is almost always around 7, which likely means one of two things:

• Bromothymol doesn’t have it’s own pH, adapting to the fluid (We later realized this was true), 
• OR the bromothymol’s pH level is 7, and that level is, for some reason, not affected by CO² (we later realized this is false)

We only have the bromothymol-water solution provided to us by Mr. DeGelder, a science teacher at our school, so therefore we’re unable to test the pH of the raw bromothymol itself, due to its most basic form being a powder. As we’ll mention in a bit, the pH of the raw bromothymol-water solution we got could be slightly inaccurate.

We noticed that after the person had exercised, their heart rate skyrocketed from the 80s and 90s to the 130s and 150s. Also, we noticed that the water colour changed quite significantly after the person exercised, turning into a lighter shade, meaning that more oxygen was inhaled, and more CO² was exhaled. Evidence of this is the fact that during the trials without exercise, generally the colour was darker and more blue-ish, but after exercise, the colour was more lighter and greenish. Generally, the lighter the colour of water, the more CO² is being utilised, and while the pH didn’t change much, we realized that bromothymol doesn’t have its own pH, instead remaining the same as the fluid it resides in. We also realized that CO² doesn’t affect pH levels significantly from what we tested, even in combination with bromothymol. Thus, the colour of the water proved to be a more deciding factor in our experiment, to aid us in supporting our hypothesis.

 

Below, we talk about data and observations from our second experiment

First of all, let's talk about why we even did a second experiment in the first place:

After our first experiment, we realized a lot of things could be changed to improve our experiment, such as measuring how long it takes to change the water to a certain colour, while also testing whether distilled or tap water would be more accurate.

We filled one respirator with tap water and the other with distilled water. For the tap water respirator, we noticed the starting colour was teal, and the distilled water respirator starting colour was yellow, as opposed to the deep blue of the first experiment we conducted. We’ll explain some of our theories for why this could be later. 

We conducted another set of trials and the data is below.

 

Before we started, we took pH measurements of plain tap water and distilled water. The tap water’s pH was 7, and the distilled water’s pH was 6. The distilled water had ozone which is slightly acidic, leading to this measurement.

Underneath are tables of data gained during our second experiment

Navneeth(resting)

Trial #	Time to change colour (seconds)	Colour of water
1	D: 18 T: 21	D: Gold Yellow T: Deep green
2	D: 13 T: 22	D: Gold Yellow T: Deep green
3	D: 11 T: 20	D: Gold Yellow T: Deep green

 

Shreyas(resting)

Trial  #	Time to change colour (seconds)	Colour of water
1	D: 13 T: 20	D: Gold Yellow T: Deep green
2	D: 16 T: 20	D: Gold Yellow T: Deep green
3	D: 19 T: 20	D: Gold Yellow T: Deep green

 

  

                                           Navneeth(exercising)

Trial #	Type of Exercise	Time to change colour (seconds)	Colour of water
1	Jumping Jacks	D: 13 T: 17	D: Gold Yellow T: Deep green
2	Jumping Jacks	D: 13 T: 14	D: Gold Yellow T: Deep green
3	Jumping Jacks	D: 13 T: 19	D: Gold Yellow T: Light green

 

 

                                                Shreyas(exercising)

Trial #	Type of Exercise	Time to change colour (seconds)	Colour of water
1	Jumping Jacks	D: 13 T: 18	D: Gold Yellow T: Deep green
2	Jumping Jacks	D: 13 T: 20	D: Gold Yellow T: Deep green
3	Jumping Jacks	D: 15 T: 15	D: Gold Yellow T: Deep green

 

 

During our second experiment, we noticed multiple things, such as:

• The starting colors of the bromothymol in our respirators being different than our first experiment.
• Distilled water generally changing color faster than tap water.

We believed that the starting colors of our respirators being different could be because of 2 reasons.

• In our respirator with distilled water, we noticed that the distilled water we used contained ozone, an acidic solution, moving our water’s pH level down from 7 to 6, where it had been for the majority of our last experiment.
• The bromothymol we got from Mr. DeGelder may have aged, which could have affected its colour. Further evidence of this is proved that when we placed the bromothymol in our respirators this time, it was noticeably green and we had to mix it a lot to make it into the colours we need.

 

We also realised that the theory we made earlier about the bromothymol having its own pH is false because overall, we noticed that it was external factors, such as ozone and the type of water we used, that changed pH level.

Overall, we believe that our second experiment provided much more valuable information than our first one for 2 reasons:

• One issue with the first experiment was that the water always ended up changing to a green/teal colour after a certain amount of time. This didn't help compare the level of exercise to carbon dioxide levels that well. 
• So, measuring how long it takes to change the water colour while breathing made more sense to gain a better measurement of a person’s carbon dioxide output. This way we were able to identify which activity produced higher carbon dioxide(resting vs exercise). 
• Also, with multiple experiments, we had more data to support our hypothesis with, proving our ideas more effectively.

Images from our experiments

Our respirators ahead of us putting in our bromothymol-blue solution. we used a tube at the top which we breathed in to exhale carbon dioxide into it, and the safety valve at the top was used to prevent accidental ingestion of the chemical bromothymol blue, which we later placed into our respirators.

The oxygen aerator we used between trials. Its main function was reverting the water colour back to its normal state ahead of our next trials, so we could consistently start back at the same point and with the same carbon dioxide and oxygen levels in our respirators.

Bromothymol blue, otherwise known as Bromothymol sulphonpthalien, the chemical we used in our respirators which reacts to carbon dioxide by changing colour from dark blue to teal to green and finally to yellow! This chemical was particularly useful in giving us an accurate display on how much carbon dioxide the tested person was exhaling, based on its colour and the time taken for it to change to this colour.

Our 2 respirators side by side in the second experiment. The one on the left is the one which we used distilled water in rather than tap water, evident by the fact that the bromothymol-blue and water combination in our respirator turned to a shade of yellow.

See the observations section (above) for analysis (we combined both of these sections for better context for our analysis.)

Note: This conclusion references data from both our first and second experiments

Our hypothesis was correct, as after exercising, the person’s CO² output grew higher than when they did not exercise. We believed this was because in the trials we completed during our first experiment, generally the water was rather dark and blue without exercise, while it was more light and green when we did exercise, proving they exhaled more CO2 than normal after exercising. However, we realized this data could be a bit mistaken, due to the fact that the water in our respirators almost always changed into a green/teal colour after a certain amount of time, and our perception of colour may have been rather inaccurate at times. Thus, we also gained data from our second experiment, where we measured how long it took the tested person to change the water to a certain colour (teal-green for tap water, pale-golden yellow for distilled water), and proved our hypothesis. Generally it took less time for the person to change the water colour after exercising than before (barring a few minor discrepancies).

 

Also, we noticed some other interesting things while completing the second experiment. First, we made the revelation that bromothymol may age, as when we placed it into our tap water, it turned a light shade of teal, and in the distilled water it turned evidently yellow, but during our first experiment, the water colour was generally in the dark shades of blue. This may have affected the results of our second experiment, but we are unsure. (more theories in sources of error)

 

Why is this experiment important?

• This experiment is important, as different people may do the same types of exercises, but it’s important to consider their external and internal circumstances to make sure they’re not over-exerting themselves.

 

• This experiment could be used by people (especially those with lung issues) to determine their CO₂ output for various exercise routines, Helping them manage their routine properly without affecting their health. 

 

• Some people may have a condition known as exercise induced asthma, it is important for them to understand their blood oxygen levels and CO2 output to not overstress themselves.

How could this project be improved on?

• We could have completed different types of exercise other than jumping jacks, such as aerobic exercises like running, etc to see if they were as demanding as anaerobic exercises(which we did).

 

• If we wanted to expand on this project, we could purchase digital pH strips so we could have more accurate, decimal precise, measures of pH.

 

• The usage of chemicals such as NaOH(Sodium Hydroxide) in our respirators would also actually allow us to measure the true CO2 output of the tested person, rather than tracking it in different methods such as what we did.

How exactly can this design be improved for use in the real-world?

• There are ways that this design could be improved, to show more precise results. One could compare the duration to change water colour exactly based on HR and pH.

 

• There could also be a proper colour evaluation done using HEX or RGB colour codes. 

 

• As for the actual design, the respirator is currently made in a bottle, however it can be made in a larger container with power operation and a built in aerator with some form of AI to detect when the bromothymol is at its original state. This allows for efficiency as well as use outside of science experiments.

Why is this project important to us, personally?

• Shreyas: This is important to me because it gives me a sense of hope for thousands across the world who don’t have optimal health care access. Relatively simple medical devices like this can mean a lot to people who can’t access or afford medical care, and it can tell them whether to seek help, whether that be at a family member, friend, doctor, or even the ER. My grandpa was diagnosed with dementia, and later pneumonia, and unfortunately didn’t make it back home. A medical grade version of this could possibly shown us the signs of reduced breathing, and we could’ve given him help sooner, to possibly reduce the effects and maybe save his life.

 

• Navneeth: This is important to me as I have a sibling who has asthma. From a personal view, I understand how completing different forms of exercise to a normal level may be difficult for some people who have this lung problem, but this respirator would make it so people would know what levels of exercise suit them, ensuring they do not overexert or physically challenge themselves any more than people who may not have these issues do.

 

• The bromothymol blue solution was made with tap water instead of distilled water or sodium hydroxide because our school didn’t have distilled water, and sodium hydroxide wasn’t prepared before winter break. This may have affected the results since tap water contains impurities that could contaminate the solution and interfere with pH testing.

 

• Before and after aeration, the bottle caps on our respirators were open, which may have allowed gases to escape and affected our results. This air loss could also have let in foreign gases, particles, or substances, potentially impacting the bromothymol-water solution. Additionally, the vent tube, while necessary for gas flow during respiration, may have introduced foreign gases. However, keeping the lid open was unavoidable for taking measurements like pH and color readings.

 

• The pH strips provided only whole-number readings (e.g., 1, 2, 3) rather than decimal values. While unavoidable, a more precise measurement would have allowed us to gain a more suitable result based on the trial. For example, if a strip showed a pH of 6 but the actual value was 6.9, it could have led to inaccurate conclusions and affected our results. This also made the bromothymol solution appear too acidic or basic in some trials.

 

• During our second experiment, the bromothymol solution wasn’t blue as expected. Instead, it appeared teal with tap water (green before mixing) and yellow with distilled water. This could be due to the bromothymol aging over the week between experiments, differences in the water (potentially from changes in city water processing), or the use of ozonated distilled water, which naturally has higher acidity. These factors changed our understanding of bromothymol, and we believe this trial was valuable in learning more about the interactions between water, bromothymol, and CO₂.

 

• Our perception of colour (particularly in our first experiment) may have been rather subjective, and we could have added images of these experiments into our observations to avoid any bias from us. However, we attempted to fix this in our second experiment by tracking time, and we believed this aided us more by preventing any forms of this bias/subjectiveness.

 

Works Cited

Science Madness. “Bromothymol blue.” Sciencemadness.org, 2021, https://www.sciencemadness.org/smwiki/index.php/Bromothymol_blue. Accessed 4 January 2025

 

Science Buddies. “Effects of Exercise: Changes in Carbon Dioxide Output.” Science Buddies, 1 May 2021, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Zoo_p013/human-biology-health/exercise-changes-in-carbon-dioxide-output.  Accessed 5 December 2024. (This was the source of the actual experiment idea which we expanded on, so huge credit here!)

 

Brittanica. “pH.” Brittanica, 2016, https://www.britannica.com/science/pH . Accessed 22 February 2025.

 

Notes we took in class, and general knowledge.

 

All of the information included here is also demonstrated on our slideshow for our project, which we first submitted to our teachers.

This project took a lot of effort, so we’d like to thank some people that made the whole process a lot clearer, easier and fun to do:

 

Thank you…

...To the CYSF committee, for organizing such a wonderful opportunity for school students to participate in in the Calgary Youth Science Fair!

…Ms. Martin, our science teacher, who introduced us to body systems in class and corrected any mistakes she saw in our work for this year’s science fair, as well for approving our proposal form as well. She also gave us helpful tips to improve our project ahead of the CYSF.

…Mr. DeGelder, our school's science fair coordinator, for supplying us with information, help, as well as preparing 11 times the amount of bromothymol-blue we actually realized we needed! He also coordinated a bunch of meetings to get us up to speed with how the registration and other processes work.

And last but not least, we would like to give a big thank you to our parents, for supporting us both throughout this project in various ways, such as supplying us with most of the materials needed for our project, and providing us with some advice we valued to ensure a high level of accuracy in our trials.