Figure 1
Introduction The respiratory system has two main roles: exchanging oxygen for CO2 in the blood and maintaining stable blood pH through regulation of the CO2 level. At rest, we exchange about 0.5 L of air with each breath. This is tidal air. When taking a deep breath we can inhale up to 3 L of air. This is called aspiratory reserve air. At the end of a normal exhalation, we can exhale with effort an additional volume of 1 L of air. This is the expiratory reserve volume. Still, a volume of 1.5 L remains unchanged in our lungs. This is the residual volume. At rest, we breathe an average of 8 L air volume per minute (an average exchange of 0.5 L in a breath, multiplied by 16 breaths per minute). During strong physical effort, we can exchange 4 L in one breath. This is the vital capacity, our whole expiratory reserve volume. CO2 concentration in the atmosphere is very low, only 0.03%. In the lungs, however, the concentration rises to as much as 7%, while in the air exhaled from the lungs it reaches a concentration of 5.1%. In this experiment, the exhaled air is bubbled into a NaOH solution. Dissolution of CO2 in water leads to the following reaction: (1)
CO2 + 2H2 O ⇌ H2 CO3 + H2 O ⇌ H3 O+ + HCO3−