Dry ice acidifies water. Dry ice is solid carbon dioxide (CO2). When dropped into water, it sublimes, i.e. turns to gas directly from a solid state. Some carbon dioxide forms weak carbonic acid with water, H2CO3. In this sequence, water has universal indicator added. It changes the color from green (neutral) to orange-red, signifying acid formation. The white smoke is a fog or mist of water droplets.