Phy 122L/132L
Pre-Lab: Ideal Gas Law
Name:
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Choose the best answer. See the lab manual for definitions of variables used in this lab.
(10 pts total; 2 pages)
1. The volume of a fixed amount of ideal gas is directly proportional to its temperature when the
pressure is held constant. Which law is this?
a. Boyle’s law b. Charles’s law
c. Ideal gas law
d. State of gas law
2. The pressure of a fixed amount of an ideal gas is inversely proportional to the volume when
the temperature is held constant. Which law is this?
a. Boyle’s law b. Charles’s law
c. Ideal gas law
d. State of gas law
In our lab, we will use a 2-liter soda bottle and a PASCO tube to verify Boyle’s law. We can
rearrange the Equation of State of an Ideal Gas to the following:
⎛ nRT ⎞ 1 ⎛ V0 ⎞
(eqn 4)
L = ⎜
⎟ − ⎜ ⎟
⎝ A ⎠ P ⎝ A ⎠
where V0 is the volume of the air in the 2-liter bottle plus the connecting tube, L is length
PASCO tube; A is cross-sectional area of PASCO tube, and P is pressure. Questions 3-6 refer to
a plot of air column length versus inverse pressure, L vs. 1/P (“y” vs “x”).
3. Should the plot yield a curved line or a straight line?
a. curved line
b. straight line
4. What does the slope of the plot represent (what is it equal to symbolically)?
a. L
b. 1/P
c. nRT/A
d. –V0/A
e. V0/A
f. (πD2L)/4
5. What would the y-intercept represent (what is it equal to symbolically)?
a. L
b. 1/P
c. nRT/A
d. –V0/A
e. V0/A
f. (πD2L)/4
6. What should V0 be approximately equal to?
a. 2000 ml
b. 2x10-3 m3 c. 2 liters
d. All of the above
e. None of the above
Questions 7-8: In the Ideal Gas Law experiment, the volume of the air in the cylinder is changed
by adding weights to the moveable piston. The piston itself has a mass of 35 grams with a
diameter of 32.5 mm. For the 80 g, mass added to the piston, an air column length of 58.1
mm was recorded.
7. What is the cross-sectional area of the piston in units of meters squared (m2)?
Show your work.
8. For the 80 g added mass (added to the piston), what is the total pressure of the gas inside the
cylinder if the atmospheric pressure is 1.000x105 Pa? Show your work.
CSU Pomona
Updated 05/13/15
Dr. Julie J. Nazareth
Phy 122L/132L
Questions 9-10 (and extra credit questions) Data was used to make a graph of air column length
versus inverse pressure (L vs. 1/P) using SI units. The origin was NOT included in the plot to
maximize the spread between the data points. A best fit straight line was drawn and two easy to
read points on the line were chosen: (x1, y1) = (9.8725x10-6 Pa-1, 0.060 m), (x2, y2) = (9.955x10-6
Pa-1, 0.081 m). Hint: questions 3-6 dealt with the same graph (L vs. 1/P), only theoretically.
Note Pa-1 = 1/Pa = m2/N.
9. Using the slope points given above, calculate the slope of the best fit straight line. Show
your work.
10. Using one of the slope points given above, and the slope calculated in question 9, calculate
the y-intercept of the best fit straight line. Show your work.
Extra Credit Question 1. Use your value of the slope to calculate the number of moles of air in
the lab apparatus. Assume the air temperature is 21°C. Show your work.
Extra Credit Questions 2. Use your value of the y-intercept to calculate the volume of the 2-liter
soda bottle plus connecting hose. Show your work.
Helpful information
Total mass = added mass + mass of piston
Weight on air column = M g
(g = acceleration due to gravity at the earth’s surface)
Pressure = P0 + M g/A
(P0 = atmospheric pressure)
2
A = area of piston = πD /4
(D = diameter of piston in meters)
Derivation of equation 4 and comparison to equation of a straight line.
(See lab manual for definition of variables)
P V
Vo +
LA
L
“y”
CSU Pomona
=
nRT
LA
= (1/P) nRT
= (1/P) nRT
= nRT/A (1/P)
= slope
“x”
where V = Vo + L A
- Vo
+ -Vo/A
+ y-intercept
Updated 05/13/15
Dr. Julie J. Nazareth