How Many Breaths of Carbon Dioxide Can Change Bromothymol Blue or Red Cabbage Solution Colors at Rest and After Exercise

To determine how many breaths of carbon dioxide it would take for a bromothymol blue or red cabbage solution to change color, we need to consider several significant factors including the concentration of carbon dioxide in exhaled breath, the volume of the solution, and the sensitivity of the pH indicator. In this article, we will explore these factors in detail.

Key Points to Consider

Carbon Dioxide in Exhaled Breath

The concentration of carbon dioxide in exhaled air is approximately 4-5% (40,000-50,000 ppm), which is much higher than ambient air. An average adult takes a breath with a volume of about 500 mL. This concentrated exhaled gas is what we need to understand to conduct our experiments.

Bromothymol Blue and Red Cabbage Indicator

Bromothymol blue is a pH indicator that changes color from blue (alkaline) to yellow (acidic) around a pH range of 6.0 to 7.6. Red cabbage juice, on the other hand, changes from purple (neutral) to pink (acidic) as the pH decreases. These indicators are crucial for determining the impact of carbon dioxide exhaled by a person on the solution.

Volume of Solution

The volume of the solution you are using can significantly affect how many breaths would be needed. For example, if you use a 100 mL solution of bromothymol blue or red cabbage juice, the amount of CO2 required to change the pH significantly will depend on the buffering capacity of the solution.

Estimation

At Rest

Let's assume a person takes about 12-20 breaths per minute at rest. Each breath contributes approximately 20 mL of CO2 from a total volume of 500 mL. For a 100 mL solution, the amount of CO2 required to change the pH significantly will depend on the buffering capacity of the solution.

After 1 Minute of Exercise

After exercise, breathing rates can increase to 20-30 breaths per minute. This means more CO2 is being introduced into the solution more quickly.