A set of quasi-quantitative experiments are described to relate volume and pressure variations associated to the phase changes of the main components of the air. The processes are promoted by variation of temperature using liquid nitrogen to refrigerate the air and get liquid oxygen, traces of dry ice and ice. The changes in volume and pressure associated to oxygen phase changes are used to discuss and rationalize phenomena as different as the effects of intermolecular forces on the properties of substances, industrial accidents resulting from a sudden pressure increase due to undesired reactions or even rationalize how popcorns are made. The ludic character of some of the experiments aims to promote the interest and curiosity of youngsters on scientific issues.
Keywords:
phase transitions; ideal gas equation; air composition; intermolecular forces
