Why the soap balls float in this experiment?

Practically all of us already played with soap balls. However, few people had the opportunity to observe them so closely and for several minutes. The soap balls are so fragile and light that easily are dragged by a breeze, or simply, they burst as soon as they touch a surface.

Being very light, the soap balls float in a gas more dense than air. In this experiment the colorless gas used is the carbon dioxide, produced by the reaction of sodium bicarbonate with acetic acid (vinegar). Due to the fact that the density of the carbon dioxide is higher than air, a carbon dioxide layer is reserved in the jar bottom. When the soap balls, full of air enter in contact with the carbon dioxide, they will float in it. As the soap balls float, its volume increases. While its volume increases, they turn heavier and heavier, sinking down. The soap balls grow because the carbon dioxide, that surrounds them, will diffuse inside them. The carbon dioxide, being more soluble in water than air, will diffuse more quickly to the interior of the soap ball. This fact is responsible for the increase of the volume and weight of the soap ball. This experience is an evident proof that the carbon dioxide is more dense and more soluble in water than air.