• Cellular respiration releases CO₂ as one of its products.

• Carbon dioxide forms carbonic acid when dissolved in water: CO₂ + H₂O <−−−> H₂CO₃
  Thus your blood becomes more acidic as you exercise and increase your respiration rate.

• Use Phenolphthalein as pH indicator: colorless in neutral or acid solutions, pink in basic (alkaline) solutions.

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PROCEDURE p. 76

Prepare the standard and experimental flasks:

Add a few drops of 0.5% NaOH to make the solution slightly basic with a medium pink color.

Divide the original flask equally into two, then use one as the standard and the other as experimental.
This will ensure that the 2 solutions are exactly the same.

Exhale into flask for 1 minute; do not stopper the flask too tight: let some air escape!
Then add 0.5% NaOH until solution returns to standard color.

NOTE: wear goggles; exhale only, do not inhale (drink)!

Repeat procedure with moderate and strenuous physical activity, 3 trials each. p. 77