Experiments with Helium-Filled Balloons

摘要

The effective molar mass and % purity of balloon-grade helium was determined using a procedure that incorporates the measurements obtained from a computer-based pressure sensor and temperature sensor, along with a digital gram scale. The results obtained from this method are consistently in the 90% to 94% purity range. This is consistent with the manufacturer's stated range 3 of 92% to 95% for balloonquality helium gas. To validate the methodology, the experiment was utilized to measure the molar mass for exhaled air, which yielded a itexhaled estimate of 28.6±2.4 g/mol (data not shown), compared to typical reported molar mass values in the range of 28.3 to 28.6 g/mol. Therefore, this experimental approach is reliable, as well as highly reproducible and readily performed at the introductory-level physics lab level. In addition, the experiment is also applicable for the measurement of gases heavier than air. Note: rather than using the textbook calculated value of 28.97 g/mol for the average molar mass of air, the above procedure can be modified slightly to obtain an experimental measurement of pair. The details for determining pair are described in the appendix.