Pre-Lab: Electric Fields

Phy 122L/132L

Pre-Lab: Ideal Gas Law Name: ======Choose the best answer. See the lab manual for definitions of variables used in this lab. (20 pts total) 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? [1 pt] 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? [1 pt] 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 V  L      0  (eqn 4)  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.

3. Should the plot yield a curved line or a straight line? [1 pt] a. curved line b. straight line

4. What does the slope of the plot represent (what is it equal to symbolically)? [1 pt] 2 a. L b. 1/P c. nRT/A d. –V0/A e. V0/Af. (πD L)/4

5. What would the y-intercept represent (what is it equal to symbolically)? [1 pt] 2 a. L b. 1/P c. nRT/A d. –V0/A e. V0/Af. (πD L)/4

6. What should V0 be approximately equal to? [1 pt] a. 2000 ml b. 2x10-3 m3 c. 2 liters d. All of the above e. None of the above

7. 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 added weights of 0 g, 40 g, and 80 g, air column lengths of 81.9 mm, 69.8 mm, and 58.1 mm were recorded, respectively. Complete the following table. [6 pts] Area of Total Inverse Piston, A (m2): Weight on pressure of Length of pressure, Mass added, Total mass, air column, gas (air), air column, 1/P -6 2 Ma (kg) M (kg) W (N) P (Pa) L (m) x10 (m /N) 0.0 0.035 0.343 0.0819 9.95883 0.040 0.075 100885 0.0698 0.080 1.127 101358 9.86597 Total mass = added mass + mass of piston Weight on air column = M “g” 5 Pressure = P0 + M “g”/A (P0 = atmospheric pressure. Assume P0 = 1.000x10 Pa) A = area of piston = πD2/4 (D = diameter of piston in meters)

CSU Pomona Updated 01/02/09 Dr. Julie J. Nazareth Phy 122L/132L

The following applies to questions 8-10. Data from the previous table 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 -6 -1 drawn and two easy to read points on the line were chosen: (x1, y1) = (9.8725x10 Pa , 0.060 m), -6 -1 (x2, y2) = (9.955x10 Pa , 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.

8. Use these points to calculate the slope and the y-intercept of the line. As always, don’t forget to include units in your calculations. [3 pts]

Slope =

y-intercept =

9. 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 work (including units) to receive credit. [3 pts]

10. Use your value of the y-intercept to calculate the volume of the 2-liter soda bottle plus connecting hose. Show work (including units) to receive credit. [2 pts]

Derivation of equation 4 and comparison to equation of a straight line. (See lab manual for definition of variables)

P V = nRT where V = Vo + L A

Vo + LA = (1/P) nRT

L A = (1/P) nRT - Vo

L = nRT/A (1/P) + -Vo/A “y” = slope “x” + y-intercept

CSU Pomona Updated 01/02/09 Dr. Julie J. Nazareth