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Can't Stand the Pressure!

  1. Jan 13, 2007 #1
    Hey you guys! I am doing a lab for my Chemistry class, and would like a little help. I am almost certain that my answers for 1-3 are correct, but I am a bit unsure about 4 and 5. Could you guys kindly check my work to see if my logic and answers are correct? If not, could you explain to me why it's not? Thanks in advance!

    1. The problem statement, all variables and given/known data

    Procedure

    Read over all the instructions before beginning.

    1. Fill the sauce pan with tap water. Set it close to the stove.

    2. Place about 2 tablespoons of water into the empty can.

    3. Heat the can on the stove until the water inside boils. This will not take long. You will see water vapor coming out of the top of the can when it is boiling.

    4. Now get ready for a surprise!

    5. Pick up the can with the tongs, immediately turn it upside down, then place the can in the water and pan.




    2. Relevant equations

    Analysis

    Hint: As you are thinking about this we want you to know that the water in the can and in the pan is only there to heat or cool the air in the can. In 5.07 you studied the relationships of temperature and pressure as it affects volume. Use this knowledge in explaining your results. Also, don't forget about atmospheric pressure!

    Before you begin the analysis think about what was actually happening to the gases inside versus outside the can. Think in terms of where the pressure is greatest, versus less.

    1. What happened when you put the can in the water?

    2. Why did this happen? Make sure you relate why this happened to the changes in pressure inside and outside the can.

    3. Why did you have to turn the can upside down? (Try the experiment again without turning the can over when you put it in the water.)

    4. What gas law would account for what happened?

    5. Explain how your choice of this gas law is supported by your observations.


    3. The attempt at a solution

    1. What happened when you put the can in the water? The can imploded.

    2. Why did this happen? This occured because as the temperature in the can decreased so did the volume of gas inside the can. This caused the pressure in the can to decrease; meaning that the pressure inside the can was now lower than the pressure outside (the surrounding pressure). As a result, the atmospheric pressure pushed the sides of the can inward.

    3. Why did you have to turn the can upside down? The can had to be turned upside down to ensure that air would not rush get inside the can, hence preventing it from filling the decrease in air volume in the can.

    4. What gas law would account for what happened? Boyle's Law

    5. Explain how your choice of this gas law is supported by your observations. Boyle's Law states that the product of the volume and pressure of a fixed quantity of an ideal gas is constant, given constant temperature. This tells us that temperature and pressure are directly proportional. This means that decreasing the temperature of the air inside the can also decreases the pressure to less than atmospheric. It's the pressure difference that crushes the can.
     
  2. jcsd
  3. Jan 14, 2007 #2

    cristo

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    Welceme to PG, Heroes. I just wanted to congratulate you on the use of the homework template; your question was very easy to read. That said, I'm not 100% confident on my Gas Laws, so don't want to answer the question incorrectly! However, this might bump your thread so it's visible to someone who can help!
     
  4. Jan 14, 2007 #3
    Is the temperature constant?

    Boyle simply stated if volume decreases pressure increases and if volume increases pressure decreases. Which makes logical sense heh :p.

    There's a temperature and volume relationship. Also a temperature and a pressure relationship. These two are covered in this persons law =).

    *Note* The outside pressure is 1 ATM and is for the most part constant =). But does the pressure inside the can change due to temperature :p [big give away]?
     
    Last edited: Jan 14, 2007
  5. May 13, 2008 #4
    i dont get this experiment....
     
  6. May 13, 2008 #5
    i dont understand #5.
    anyone wanna helP??
     
  7. May 13, 2008 #6

    cristo

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    I've deleted the last two posts in this thread, since the OP has clearly gone, and the no attempt has been made by the second student asking a question in this thread. Since she has made her own thread, I am locking this one. Direct your attention to her thread if you wish: https://www.physicsforums.com/showthread.php?p=1729029#post1729029
     
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