Have students observe which objects float. The density of raisins and peanuts is greater than water, so they sink. In soda water, the bubbles attach to the peanuts and the overall density of this combination is less than water, so they float. Even with bubbles, the overall density of the raisins is greater than the water.
Flotation is one of the methods used in the industry for extraction of minerals.
Frothers are added to the solution to lower the surface tension of the water. The froth must be strong enough to support the mineral but weak enough to break down in launders. Common frothers are alcohols and glycols. Have the students experiment with other items such as beans or shell macaroni. Have students research other types of frothers for flotation.