Chemistry 11 Lab #7/8

Lab #7/8: Gas Laws

We do not have enough apparatus to work in your regular lab groups for much of this lab. We will run through the first parts together. The last part depends on our ability to acquire dry ice.

Theory
Boyle's Law says PV=constant when n, T held constant
Charles' Law says V=constant x T when n, P held constant
Ideal Gas Law says PV=nRT (T in Kelvin) so when n, V held constant, P is proportional to T
Avogadro's Principle says that V=constant x n when P, T held constant

where P is pressure, V is volume, T is temperature in Kelvin and n is the number of atoms or molecules of gas.

For the syringe apparatus we showed in class that we expect
1/V = -mg/kA + Po/k
where k is the constant from Boyle's Law, A is the area of the syringe plunger (in m2), m is the mass hung from the syringe (in kg), g is the acceleration due to gravity (9.8m/s2), and Po is the pressure in the room (in Pa). V is in m3


For the pressure cooker we showed in class that we expect
P = kTCelsius - kTabs. zero in C

Part #1 Boyle's Law to get air pressure in CBBA

  1. Hang masses from the syringe apparatus we used in class when discussing the nature of the phases of matter. Note the volume of the syringe for each mass and put in a table of data.
  2. Graph the inverse of the volume vs the mass and use the relationship from the theory section above (which was derived and explained in class) to find room pressure.
Part #2 Ideal Gas Law (or Charles' Law) to get absolute zero

  1. Place a small amount of water in the pressure cooker and secure the lid. Place it on the hot plate and heat until the water has all evaporated.
  2. Take readings of the pressure and temperature (in Celsius) in the cooker and graph pressure vs temperature. Using the equation from the theory section calculate absolute zero by finding the x-intercept.
  3. The apparatus may not cooperate with us on this part and we will consider Charles' Law instead (V is proportional to T in Kelvin). We will Take a closed air-filled bag a place it in ice water and note the volume and then place the same bag in boiling hot water and note the new volume. A third measurement of using room temp water will allow us to graph the results to confirm Charles' Law and find absolute zero.
Part #3 Avogadro's Principle

  1. Mass two pieces of dry ice, one of about 0.2 g and another of about 0.1g. Place each piece in a balloon (or plastic bag) and tie the balloon (bag) shut. (If we can't get dry ice we will try something similar with water in the balloons. This will be more complicated and I will need to explain how in the lab.)
  2. What does Avogadro's Principle predict for the ratio of volumes of the two balloons? Do your results confirm this?
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