Experiment 1: A solution was made consisting of 100 mL of distilled water, 10 dr

Question

Experiment 1: A solution was made consisting of 100 mL of distilled water, 10 drops of 0.1N NaOH and 5 drops of phenol red indicator. The solution at this point was red. A member of the team then exhaled into the solution until the solution turned orange and then yellow. The time it took for this color transition was 96 seconds. The same initial solution was made again the same way. Again, the solution was red. The same person performed vigorous exercise for about 3 minutes. Immediately after the exercise s/he exhaled into the solution until the solution turned orange and then yellow. The time it took for this color transition was 28 seconds this time. 1. 15 ptsl Explain the results presented in Experiment 1. What is the difference between "at rest" exhalation and "after exercise" exhalation? Explain in detail why there is a difference in the two results.

Explanation / Answer

During respiration oxygen is inhaled and the inhaled oxygen enters the blood stream from where it is transported to the tissues. In the tissues, it liberates energy from the foods we eat through the process of metabolism. During this process carbon dioxide is released. The released carbon dioxide reaches the lungs from the tissues via the blood stream and from the lungs carbon dioxide gets exhaled.

After exercise, because more amount of oxygen is inhaled to meet the energy needs of the body during exercise, more amount of carbon dioxide is generated. As a result more amount of carbon dioxide will be exhaled into the atmosphere after exercise when compared to at rest.

The results of the experiment show that since the person performed rigorous exercise for 3 minutes, the amount of carbon dioxide that is generated by the person was more due to increased rate of respiration by the person during exercise. With the result when the person exhaled into the solution, the solution turned yellow in 28 seconds time when compared to the 96 seconds time taken for the transition of the solution to yellow when the person was at rest.

Carbon dioxide present in the exhaled air reacts with water to form carbonic acid which is a weak acid. Phenol red indicator is pink under alkaline conditions. Under pH conditions of less than 6.8 it turns yellow. As the amount of carbon dioxide is more in the exhaled air after exercise, more amount of carbonic acid will be generated and so the solution rapidly turns from pink to orange to yellow (28 seconds) compared to at rest exhalation (96 seconds).

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