In researching and doing an experiment about Dalton's Law, we learned a lot. We not only learn about John Dalton, but we also learned how to measure error when performing and designing an experiment. Unfortunately, in our experiment there was a great amount of error, both systemic and in measurement. However, this enabled us to work with error and prepared us for avoiding it in the future.
The knowledge of Dalton's Law is essential to all divers. To learn background information on John Dalton, please see Background Information. Dalton's law states that "each gas in a mixture creates pressure as if the other gases were not present." In our experiment, we used a lit candle to remove the oxygen. (Fire uses up oxygen while it burns.) When the oxygen was all used up, the flame was extinguished. Therefore, in our experiment, when the flame was extinguished, the pressure left in the flask should have been equal to the original partial pressure of the nitrogen. As you will read later in this essay, this did not work out exactly the way we wanted.
Regular air is made up of approximately eighty percent nitrogen and twenty percent oxygen. According to Dalton's Law, if we had performed the experiment correctly, the pressure should have gone down twenty percent, which is the partial pressure of oxygen in the air. The remaining pressure would be eighty percent, which is equal to the partial pressure of the nitrogen in the air. When we averaged the minimums and maximums from our graphs (see Results), it turned out that the pressure only went down fourteen percent. That is only six percentage points off from the twenty percent it was supposed to drop, and we are pretty sure we know why our results turned out the way they did. In our experiment, the flame was extinguished, but because the candle was so small, the flame only used up the oxygen immediately surrounding the candle. It did not use up the oxygen right near the top of the flask or right near the bottom of the flask. This affected our results in the other two mixtures of air as well. This was the systemic error in our project. It was present throughout our whole project.
We also measured the average deviation of each trial. (We performed three trails for each mixture of air.) This compares the difference of each minimum and maximum to the average of all the differences, which shows measurement error. This is the error that is present when each individual trial is conducted. As you can see, we conducted each trial similarly. The average deviation was 0.064 making it an error of 6.4%. Six percent is not a large percentage, so we concluded that our measurement error was not significant.
The next mixture of air we tested was a mixture of sixty percent nitrogen and forty percent oxygen. This is called nitrox. Testing nitrox proved to be a very difficult task because we had to fill up the flask with nitrox and allow as little regular air as possible to get into the flask along with it. Our way of filling the flask was not professional, but it worked pretty well. (See Method and Materials) Our original plan for filling the flask with nitrox was to bubble the nitrox into the flask underwater, using a balloon filled with nitrox. This would prevent any regular air from entering the flask. Filling the flask this way caused the inside of the flask to be wet when we did our experiment and as a result, the wa ter dripped onto our candle and extinguished the flame. We had to redo the experiment many times and each time we were wasting our limited amount of nitrox. Also, the wet flask forced us to be extra careful when dropping the candle into the flask. Therefore, we took longer to drop the candle into the flask, and the stopper was off the flask for long periods of time. This allowed regular air to enter the flask. We figured that blowing the nitrox into the flask above water would work better. As we stated before, this method was a bit unprofessional and it increased the systemic error in our experiment. However, we were able to perform three trials before running out of nitrox. We thought it would be better to have three trails using a less professional method than having one trial using a method we thought was more accurate. Having three trials allowed us to measure the average deviation. The average deviation of sixty percent nitrogen/forty percent oxygen was 0.124 making it an error of 12.4%. This error along with the systemic error of too much regular air and the small candle made the pressure drop 18%, which is not near the forty percent it was supposed to drop.
The third mixture we tested was fifty percent nitrogen/fifty percent oxygen. This is another form of nitrox. Testing this nitrox mixture had the same systemic error of too much regular air and the small candle, causing the pressure to drop only 22%. Our results were not near the fifty percent that it was supposed to drop. In observing these results, we noticed an interesting pattern. The pressure dropped the most but had the greatest percentage error. In testing regular air, the pressure dropped the least amount and had the least percentage of error.
We feel that our experiment worked successfully. For every trial, the pressure did not drop the amount it was supposed to drop, but it did drop. For regular air, the pressure dropped the least amount, as it was supposed to. As we stated above, it did not drop the full twenty percent, but it came close. For the sixty percent nitrogen/forty percent oxygen mixture, the pressure dropped a little bit more than the pressure in the regular air test did. However, it did not drop a whole forty percent. The same thing is true for the fifty percent nitrogen/fifty percent oxygen test.
If we were to perform this experiment again, we would make one major change. We would get more nitrox of both types. This would allow us to blow more nitrox into the flask, decreasing the amount of regular air in the flask. This would probably cause the pressure inside the flask to decrease to the amount expected. Our results would be more accurate when testing the nitrox.
In doing this project, we learned a lot about Dalton's Law, especially nitrox and nitrogen narcosis. Nitrox is mixed especially for divers going very deep and want to decrease their risk of getting nitrogen narcosis, which is closely related to Dalton's Law. Dalton discovered that gases act and affect people according to their partial pressure. At sea level, there is one atmosphere of pressure upon us. Eight tenths of that pressure is nitrogen, and two tenths of that pressure is oxygen. When divers dive, the amount of pressure upon them increases. The deeper a diver goes the more nitrogen and oxygen is being absorbed into their blood and tissues. However, nitrogen is the gas that divers should be aware. It starts out at a higher partial pressure than oxygen. When a diver reaches a certain depth, between four and five atmospheres, the level of nitrogen becomes dangerous. The diver can get nitrogen narcosis, which impairs his or her judgment and can be deadly. Divers use nitrox to prevent this. Nitrox increases the amount of oxygen that is being inhaled, therefore lowering the amount of nitrogen being inhaled. (It evens the amounts out.) This enables a diver to dive to deeper depths without breathing in too much nitrogen and getting nitrogen narcosis. Because we performed our project above water and were not able to dive past sixteen feet, we did not witness nitrogen narcosis. This is okay, though, because we would not want any of our classmates to get nitrogen narcosis and give their regulator to a fish. (That really did happen to someone!)
To conclude our analysis, we would like to thank Mr. Harlan and all our other teachers who allowed us to learn so much about Dalton's Law and the wonder of diving. Dalton was a brilliant scientist who made unbelievable achievements that have prevented the loss of many lives. There are divers who are not fully aware of the dangers of nitrogen narcosis, and doing this project made us realize how important the knowledge of Dalton really is to scuba diving. We hope this project will educate future divers and inspire them to learn more.

 


 

 

 

 

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