A student was asked to determine the concentration of an aqueous HCl(aq) solution by titrating it with 1.13 mol/L NaOH(aq) in the presence of bromothymol blue indicator.
Since burets were not available, the student used droppers for each solution and
assumed that each drop was of equal volume. It took 26 drops of NaOH(aq) to
neutralize 20 drops of the HCl(aq) solution and to reach the bromothymol blue endpoint.

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?