This mini kit contains everything you need to make your own fizzy bath bomb! What’s the secret behind the fizz? When citric acid and sodium bicarbonate are mixed together and added to water, they cause a chemical reaction. This is because the acid has a low pH and the bicarbonate has a high pH. The bubbles are caused by the sodium bicarbonate breaking down and creating carbon dioxide gas. Includes one 4.5 cm (1.75") ball mold, a packet of cornstarch, citric acid, sodium bicarbonate, and instructions. Add food coloring for your own custom look! For ages 8+ (or 6+ with adult supervision).