We really enjoyed creating and following through with our experiment on Dalton's Law of Partial Pressure. This is a very complicated topic with many extreme circumstances and even dangers. For example, we nearly lit the science floor on fire and singed the ground. Neither one of us got hurt but it was really cool. Thanks to that little accident we will always know that Mr. Harlan will never forget us and we are glad that he wont. We are proud of the experiment we designed and we are glad we were able to follow through with it. We are not happy with some of the results we ended up getting but we are still satisfied with what we got out of our experiment.
Due to our complicated topic you may get confused when reading our analytic essay. So, if you are confused at all when reading the rest of our analytic essay check our our Method and Materials in our Lab Report.
Our results show how Dalton’s Law of Partial Pressure is correct. When using normal air, our hopes were to get the pressure to drop from 100 kpa (kilo pescals) to 80 kpa. Getting the pressure to drop from 100 kpa to 80 kpa is the expected results, but this is what our results were. The normal air went from 100 kpa and dropped to about 90 kpa. After this test we looked at one another and said well that did not really go as well as originally planned. There was something causing the results to be off and we were not able to find out what exactly it was. So, we decided to carry on and see what else would happen when we tested our experiment with nitrox.
It was now time for us to conduct our same experiment with nitrox. We were going to use a mixture of nitrox that contained 40% oxygen and 60% nitrogen. Our original plans with the 40/60 nitrox were as follows. We wanted the pressure to drop from 100 kpa to 60 kpa. Of course there was a surprise that we did not exactly see coming our results were different compared to what they should have been. The 40/60 nitrox dropped to about 69.1 kpa in our first trial. As we said
there is about a 9.1 differential between what we got and what we should have gotten. In the second trail it dropped to about 62.4 kpa. That trail right there gave us the results that were closet to our original goal. In the third and final trail for the 40/60 nitrox the pressure dropped to about 66.3 kpa.
After reviewing our results from the 40/60 nitrox trails we came to a conclusion about why some of the results were a little off. We figured that there was some “unknown” factor in our experiment. This was the thing that had to be causing that little margin of error that made our results good results rather than excellent results. We were disappointed because we had no idea what was causing the error. We also had some fears that it would continue to play a large part in error throughout our whole experiment.
After our mixed results with the 40/60 nitrox we were now ready to move on to a different form of nitrox. This nitrox was a mixture that was made up of 50% oxygen and 50% nitrogen. In this section of our experiment our hopes were to have results that were somewhat close to what our goal was. The pressure was supposed to drop from 100 kpa to at least 50 kpa. Of course, due to that “unknown” factor in our experiment, it almost seemed impossible for us to attain excellent and almost close to perfect results. In our first trail the pressure dropped from 100 kpa to about 65.8 kpa. Right there you can already see that our results are off by 15.8 kpa. That is not very good data. So we pushed on and ran a second trail. In our second trail the pressure dropped from 100 kpa to about 67.2 kpa. We were now saying to one another “Wow that’s worse than our trail before.” We were beginning to worry if our data would be completely useless by the end of the experiment. There was only one way to find out so we ran one more trail with the 50/50 nitrox. In the third trail the pressure dropped from 100 kpa to about 66.3 kpa. Once again our results were off by quite a bit.
The unknown error was one thing that disappointed us more than anything in our entire experiment. It through off our results and made our experiment less accurate than we had originally hopped it would be. This whole principal of the “unknown” factor led us to our discussions about error and how it fit into our experiment.
Error played a large role in the outcome of our experiment on explaining
and proving Dalton’s Law of partial pressures. It is almost impossible
to run an experiment without some degree of error. There were numerous occasions
in which our results could have been altered by error. For example, there
could have been air leaks in the plastic bag and the pressure sensor. When
we filled the yellow bags of air we were hoping that were would be no hole
or opening in the bag through which the air could leak out. If there was
a hole in the bag that we did not notice, then some of the nitrox could have
leaked out. This would have altered the balance of oxygen and nitrogen in
the bag and our results could have been filled with error. Another major
place where error occurred was when we inserted the rubber stopper (with
the pressure gauge and temperature sensor inside of it) into the glass beaker.
The particular pressure sensor that we used was very sensitive. By pushing
the rubber stopper into the beaker we created a higher pressure than normal.
Other errors that occurred with the pressure gauge were leaks in the tubing.
The tube that connects from the rubber stopper to the interface developed
leaks if it was pulled or moved in an awkward direction. The slightest hole
or leak in the pressure sensor could have thrown off our results and caused
a lot of error. Another large area where error could have occurred was in
the lime water. The lime water was inside the beaker to do one thing, absorb
the carbon dioxide. On a couple of trials it seemed as if the lime water
was not working as well as we hoped it would. We found out that it worked
betters when you shook it around so it could spread out and absorb more carbon
dioxide. There also might have been to much carbon dioxide for the lime water
to absorb and so pressure from the CO2 was still there. The largest form
of error that we found in our experiment was the unknown that we talked about
earlier. It was the one thing that probably caused the most error. The thing
that was so frustrating was we did not even know what it was. However, we
finally figured out the almost ever single experiment or study that is conducted
has an “unknown” error.
The formula for Dalton's Law of Partial pressure is P total = P1 + P2 + P3 + .......Pn. In other words the total pressure of a mixture of gasses is equal to the sum of each individual gas in the mixture. Some of our results proved to be very close to what the formula predicted would happen, but other parts of our results were way off. For example in the 50/50 nitrox test the formula stated that the pressure must drop from 100 kpa to at least 50 kpa. You can see in all of our trails with the 50/50 nitrox the pressure never dropped below 60 kpa. This may have to do with the “unknown” error that we were not completely aware of. Another example of it not being anywhere close to the formula was in our 40/60 nitrox trail. In this area of our experiment, the formula stated that the pressure would drop from 100 kpa to about 60 kpa. This never happened in any of our trials except for maybe one or two. This again might have been caused by this “unknown” variable.
After we reviewed our results we started to crunch the numbers down and find out what our percent of error was. This is a chart showing our percent error and the average of each trail.
By doing this experiment, we learned all about Dalton’s Law of Partial pressures. We learned that with a mixture of gasses in a container, the total pressure is equal to the sum of the pressures of each gas in the mixture. Mr. Harlan told us that this experiment was a challenge and was a difficult law to understand. We saw how the law of partial pressures was confusing with many unknowns and possibilities of error. The type of gas we used was called Nitrox. We used different mixtures of it such as 40 oxygen/60 nitrogen and 50 oxygen/50 nitrogen. Divers use the mixtures of nitrox when diving at great depths when they need a different balance of oxygen and nitrogen. If there is too much oxygen it would poison the diver. However, if there was not enough oxygen the diver would suffocate. The total pressure of the air in the tank also must be equal to the pressure on the outside “environment” or else the lungs of the diver would collapse. These were all very important things that we learned about Dalton’s Law and how it affects people when they scuba dive. Dalton’s Law explains the many symptoms or harmful things that can happen to a person when he/she scuba dives. For example, nitrogen narcosis is a state similar to alcohol intoxication but you are underwater and you get completely clouded. We learned all of these things in our experiment about Dalton’s Law of Partial
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