Which is a sign of a chemical change? a) ice cream left at room temperature melts. b) calcium chloride is dissolved in h2o and disappears. c) paint on a freshly painted wall dries and is no longer sticky. d)when h2s gas is bubbled into a lead acetate solution, a precipitate forms.

You exhale co2 which is produced during cellular respiration.  co2 combines with the water in your blood's plasma to make up one half of the body's most important buffer pair, carbonic acid.  the more physical activity you engage in, the more co2 your body is producing.  you can see this by putting some of the cabbage indicator in a glass and then blowing bubbles into it through a straw.  can you see a change in the color of the indicator?