A solution was made consisting of 100 mL of distilled water, 10 drops of 0.10M N
ID: 100298 • Letter: A
Question
A solution was made consisting of 100 mL of distilled water, 10 drops of 0.10M 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 to occur was recorded below. The solution was discarded. Another solution was then made with 100 mL of distilled water, 10 drops of 0.10M NaOH and 5 drops of phenol red indicator. The solution at this point was red. A member of the team then performed vigorous exercise for about 5 minutes. Immediately after the exercise the team member exhaled into the solution until the solution turned orange and then yellow. Again, the time to color transition was recorded below. Using your knowledge of the purpose of phenol red, describe the acidity (acidic or basic) and pH ( 7) of the solution at the beginning and at the end of this experiment. a) Beginning b) End: Explain the results presented in Table 1. There is a difference between the results from the two experimental conditions (at rest and immediately after exercise). Considering your answer to #2, 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
1) a) beginning
Basic and pH is >7
b) end
Acidic and pH is <7
2) Phenol red is a pH sensitive indicator. When we exhale into the basic water with Phenol red indicator the air which we exhaled has the carbon dioxide and it reacts with water and makes the Carbonic acid(H2CO3) and this decrease the pH. Decrease in pH change the colour of Phenol red indicator to subsequently red to yellow.
In the resting phase the rate of the exhalation was low so the amount of carbon dioxide will be less transferred in the flask and the change in the pH will be slow.
After doing vigorous exercise the exhalation rate is very high so transfer of carbon dioxide is much faster. So more carbon dioxide will react to more water and make more Carbonic acid and change in the pH will be much more faster
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