|MadSci Network: Chemistry|
Dear Haley, Your mother is correct when she says the bubbles are carbon dioxide. The water is there only as a solvent, something that converts the two solid reagents into liquid (solution) so they can react. Your interest in chemistry is encouraging, keep it up! Milk is a reasonable substitute for water as it is mostly water, but vinegar would short-circuit the reaction by making bubbles before the citric acid had a chance to react. Lemon juice also contains citric acid so it would add little to the situation. Signed: Mad Scientist Adjunct
Try the links in the MadSci Library for more information on Chemistry.