(1) According to the ingredient list of soda water, the raw material citric acid needs to react with sodium bicarbonate of baking soda to generate carbon dioxide, so the answer to this question is: citric acid, baking soda (or sodium bicarbonate);

(2) Carbonic acid is unstable and easily decomposed to generate carbon dioxide. Clarified lime water is used to test carbon dioxide, which can make clarified limestone turbid, so the answer to this question is: the method of guessing and hypothesis verification and the phenomena observed in operation. The gas can be carbon dioxide, and the gas generated by soda water is introduced into the clarified limewater to make the clarified limewater turbid.