Liquid nitrogen is -196˚C and quickly freezes the ingredients into ice cream. The nitrogen boils out leaving deliciously creamy ice cream. The “fog” that we see is condensed water vapor though, not nitrogen gas.
When basic baking soda (NaHCO3) is combined with acidic lemon juice (mainly citric acid, H3C6H5O7) an acid base reaction occurs. The reaction releases CO2 which can be captured using dish soap to form bubbles.
Universal indicator goes from red (pH 4) to violet (pH10) as the pH of a substance changes. Adding NaOH to water starts the solution off at pH 8-9 (blue). When dry ice is added to water it forms carbonic acid, and lowers the pH, which is the reason for the color changes. The “fog” that we see is condensed water vapor though, not carbon dioxide gas.
This demo uses acid base chemistry and an indicator to make an ink that will appear or disappear depending on the solution added to it. Phenolphthalein, which is clear, reacts with a base, and then turns pink.