This experiment explored how aerobic respiration from exercise affects a basic solution and its transition to an acid. More energy is used during exercise, more oxygen is required in the human body to fuel cellular respiration. Cellular respiration produces energy in the form of ATP and releases CO2 as a byproduct. It’s equation is glucose + oxygen → carbon dioxide + water; C6H12O6 + 6O2→ 6CO2 + 6H2O. (Dimand et al, 2002). This supports the prediction that longer durations of exercise will result in higher rates of carbon dioxide produced.


To investigate the effects of aerobic respiration, four Erlenmeyer flasks were filled with distilled water to have a starting point with a neutral pH level. Half a pipette of Bromothymol Blue was added to the water as an acid indicator with colors that ranged from acidic yellow to neutral green, then basic blue.

Three people performed the exercise of running stairs for increments of one two and three minutes, so respiration could be reached. Each person blew through a straw into the solution and measured the amount of time it took to change the neutral green water to acidic yellow with the addition of carbon dioxide.

Sodium Hydroxide (NaOH) is a base that was used to return to the neutral state that was measured against the control flask of green distilled water so we could ensure consistency. The times for each increment were recorded, averaged, and graphed on a scatter plot to depict the trend.


This data concludes that as the duration of exercise increased, the time it took to change the flask from a neutral to an acid both increased and decreased. The predicted outcome was that the time to turn to acid would decrease as exercise duration went up, This is supported by the fact that higher exercise rates mean increased respiration which produces more CO2 that changes a base to an acid. 

The exhalation of carbon dioxide into the substance created a carbonic acid, which led to a change in the pH level. This change was indicated by bromothymol blue, seeing that the substance reverted from a green color to its yellow acidic state. As seen in Graph 1 there is not much data because the averages of all of the trials were taken which was only four points and they had a weak correlation, so a trend cannot really be produced.

The experiment was controlled by matching the neutral starting point to a control flask that was a set green color. This along with the fact that resting heart rate was reached before each trial ensured that everything started at the same point.

Some errors could be found in the fact that there was soap residue in some of the flasks that caused the mixture to foam up and prohibited it from turning all the way to an acid because soap is basic. This could be resolved by rinsing the flasks well with water before use. This would prevent inaccuracies in the time it takes to change to acidic.

The faster the rate of respiration, the greater the rate of oxygen use and the greater the rate of carbon dioxide release (BBC, 2014). With knowing this, one could predict that if someone were to exercise very rapidly, more and more and more carbon dioxide would be expelled. Another question that could be researched is whether different types of exercise cause more respiration compared to others with variables of activity and time it takes a basic solution to become acidic.

Works Cited:

BBC. (2014). Respiration. Retrieved November 21, 2017, from

Dimand, J., & B. B. (2002). Respiration Rates among exercising and resting crickets. Retrieved November 20, 2017, from

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William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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