Students determine the molecular weight of a pure gas in a balloon by using gas laws and trapping the gas in a glass bottle. Students watch the instructor demonstrate the lab on day one. On day two and three they practice the lab. On day four we discuss the lab and all the calculations. On day 5 students team up and complete a lab quiz. Their instructor fills their balloon with an unknown pure gas from a storage tank. Students are awarded points based on how close they report the gas mass.