You blow up an ordinary party balloon with air until it has a diameter of 6 inches. Your friend blows up another balloon with helium gas until it has a diameter of 12 inches. Air consists mostly of O2 and N2 molecules, while helium gas consists of He atoms. Assume the pressure in each balloon is the same. What is the ratio the number of helium atoms to the total number of O2 and N2 molecules?
Air is about 80% nitrogen and 20% oxygen. What is the ratio of the weight of the helium balloon to the weight of the air-filled balloon?
(Hint: Imagine that there are 80 helium atoms in the helium balloon. Calculate the mass, in atomic mass units, of this amount of helium, and then compare it to the mass of the corresponding number of oxygen and nitrogen molecules.)