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Gases- Yo_ _Ch.13 14_

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					Nature of Gases
   (ChemCom Lab)

 Ch.13 & 14 in your text
   Station #1: Massing the balloon
                                                             Air molecule
                                                                 Inflated balloon


                                                                  Deflated balloon




                                                .890 g               .670 g



What did this station show?
Air has weight: your balanced showed a difference in mass meaning air has
mass even though it is invisible and we think of it as being weightless.
                              Station #2
           What we did: Lowered inverted glass
           into water…then tilted it.                                 Bubbles! Show us
                                                                      presence of gas



                                                                  er
           Cup/beaker                                          ak
                                                          p /be
                                                     Cu




         Beaker of Water                         Beaker of Water



What did this station show?

Air occupies space: Since the water did not enter the glass until tilted, air
molecules take up space (they are a part of matter)…when the glass is
tilted, air escapes and rises showing that it is less dense than water.
                              Station #3
                               Tried to blow up a balloon in a bottle.



                                                       Balloon



                                                           arrows show
                                                           pressure: collisions
                                                           against the sides of
                                                           bottle and the sides
                                                           of the balloon.


What did this station show?

Air has pressure and exerts pressure on both sides of the balloon.
The balloon can be blown up a little bit….gases can compress.
                            Station #4
                                       What we did:
                                       Filled test tube w/water, put plastic on
                                       top, inverted.




What did this station show?
Air exerts pressure in all directions. Air pressure, acting upward against
the covering, supports the weight of the water and prevent it from spilling
out of the container.
                            Station #5
                                     What we did:
                                     Filled bottle with two holes in it, with
                                     water. Put cap on tightly, removed
                                     finger from hole.

                                        holes
                                                What happened?:


                                      When both holes are unblocked, water
                                      flows through one of them, when one of
                                      the holes is blocked, the water stops
                                      coming out the other hole.
What we learned:
Air exerts pressure in all directions- the external pressure of the atmosphere
prevents water from coming out.
Station #7 (6 was drawn Tue-Wed)
                        Test tube of water

                               What we did:
                               Filled test tube with water, put plastic on
                               opening, inverted, put in beaker, move up
                               and down keeping mouth of test tube
                               immersed in water.

                           What happened:

      Beaker of H2O           The water remained in the test tube
                              regardless of how high or low the test
                              tube was.
                            What does this mean?

Air molecules are exerting an equal pressure on the water in the
beaker compared to the pressure of the water caused by gravity.
                         Station #8
                                   What we did:
                                   Drew air into the syringe, covered hole
                                   with finger, pushed plunger and let go.
                                   What happened:
                                   Compress plunger a little bit, but not
                                   much.

                                     Gas simulation

  What this tells us:

Gases are compressible since we could move the plunger a little bit.
Since it became more and more difficult to push the plunger we know that
the pressure increased as we decreased the volume.
                          Station #9
                          What we did:
                          Two balloons of same size. Submerge one into
                          a cold water bath and the other into a hot water
                          bath. Take them out and compare.



                          What happened:
                          Cold balloon- gets smaller,
                          Warm balloon- gets bigger


                                                   Different gas simulation
What this shows us:
Temperature and volume are directly related. If one increases the other
increases…if one decreases, the other decreases. Car tires?
Questions from p.250 of ChemCom
              book.
1) Which experiments are useful in demonstrating that air is
   matter?   #1 & #2: matter is anything that has mass and takes up
                space.
2) Which experiments are useful in demonstrating that air exerts pressure?
        3, 4, 5, 6 & 7
3) Explain any differences b/n your predictions and the actual
outcomes of the experiments

 4)…we just did this… J

 5) Explain an additional activity/experience that you have had that
 demonstrates that        a) air is matter          b) air exerts pressure
Crazy Stuff
               Gas Pressure
Pressure = the force exerted on a certain amount
  of space on an object.
                               Balloon Demo…

                       4 units for Pressure (that we will
                          study):

                       1) mm Hg (millimeters of mercury)
                       2) Torr = pressure of 1 mm Hg

                       The unit most barometers use to
                         measure the pressure caused
                         by the atmosphere.
 3. Pascal (Pa) or kPa = 1,000 Pa
      -SI unit of pressure

 4. Atmosphere (atm) = the pressure required to
 support 760 mm Hg in a mercury barometer at 25oC.


Conversion:
1 atm = 760 mm Hg = 101.3 kPa = 1 torr

				
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posted:7/14/2013
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