Name ______

Unit 7

Gases and the Kinetic Molecular Theory

Chemistry: Unit 7 Outline: Gas Las

Assignment / WB Page Number / Must be done at school / Done?

Podcast 7.1 Intro to Gases / Online
Worksheet 7.1
Podcast 7.2 Gas Laws / Teacher Handout
Worksheet 7.2 / Pg 12-13

Lab: Boyles Law

/ Online / x

Take Home Lab: Pressure and Balloons

/ Pg 4-5
Lab: Charles’ Law / Pg 6-8 / x
Podcast 7.3 Combined Gas Law / Pg 14-15
Worksheet 7.3 / Online
Podcast 7.4 Ideal Gas Law / Teacher Demo
Worksheet 7.4 / Pg 16
Podcast 7.5 Graham’s and Dalton’s Laws
Worksheet 7.5
Demo: Graham’s Law / x
Podcast 7.6 Gas Stoichiometry
Worksheet 7.6
Lab: Stoichiometry and Gas Laws / Pg 9-11 / x
Podcast 7.7 Molar Mass of Gas / Pg 19-21
Worksheet 7.7 / Pg 22
Unit 7 Review
Lab Test: MM of Butane / In class / x
Unit 7 Exam / In class / x

Unit 7 Vocabulary

Boyle’s Law

Charles’s Law

Gay-Lussac’s Law

Combined Gas Law

Ideal Gas Law

Ideal Gas Constant (R)

Dalton’ s Law of Partial Pressures

Effusion

Graham’s Law of effusion

Diffusion

Take Home Lab: Gas Laws

Purpose: To determine the atmospheric pressure at a location that has a different altitude than Woodland Park.

Materials: A balloon, a tape measure, and a string

Procedure:

  1. Blow up a balloon either at a lower altitude (Colorado Springs) or a higher altitude (Woodand Park), and take the balloon to the other location. You could also fill the balloon up in Woodland Park and then go skiing and measure the diameter of the balloon at the top of Hosier Pass.
  2. Measure the circumference of the balloon in the first location. This is probably best done with a string.
  3. Drive to location 2 and measure the circumference of the balloon.

Calculations:

  1. In the interest of making the calculations simple, we will assume that the balloon is a sphere.
  2. Using the equation C=2πr, determine the radius of the balloon in both locations.
  3. Using the equation V=4/3πr3, determine the volume of the balloon in both locations.
  4. Assuming that the pressure in Woodland Park is 571 torr, determine, using Boyles Law, the pressure in location 2.
  5. Use the table on the next page to determine your percent error. You may need to use a program like google earth to determine the altitude for your two samples. The graph below only shows form about 6500 feet up to 15,000 feet. The pressure unit is in millibars: 1mb = 0.75 torr

Data Table

Circumference of Balloon at lower Altitude
Radius of balloon at lower altitude
Volume of balloon at lower altitude
Circumference of Balloon at higher Altitude
Radius of balloon at higher altitude
Volume of balloon at higher altitude
Pressure in Woodland Park / 571 torr
Pressure at Location 2

Questions

  1. Discuss, using the kinetic molecular theory, why the balloon shrunk or grew at different altitudes. Use a picture in your explanation.
  2. What would happen if you took your balloon to the top of Mt. Everest (average pressure = 253torr), the tallest point on the earth?
  3. Explain why air pressure goes down the higher you are in altitude.

For Credit: You must have a signed note from your parent/guardian explaining two things:

  1. Why does air pressure go down as you go up in altitude
  2. Why does a bag of potato chips purchased in Colorado Springs expand (and sometimes, blow up) when brought to Woodland Park?

Boyle’s Law: Pressure-Volume
Relationship in Gases

The primary objective of this experiment is to determine the relationship between the pressure and volume of a confined gas. The gas we use will be air, and it will be confined in a syringe connected to a Gas Pressure Sensor (see Figure 1). When the volume of the syringe is changed by moving the piston, a change occurs in the pressure exerted by the confined gas. This pressure change will be monitored using a Gas Pressure Sensor. It is assumed that temperature will be constant throughout the experiment. Pressure and volume data pairs will be collected during this experiment and then analyzed. From the data and graph, you should be able to determine what kind of mathematical relationship exists between the pressure and volume of the confined gas. Historically, this relationship was first established by Robert Boyle in 1662 and has since been known as Boyle’s law.

OBJECTIVES

In this experiment, you will

  • Use a Gas Pressure Sensor and a gas syringe to measure the pressure of an air sample at several different volumes.
  • Determine the relationship between pressure and volume of the gas.
  • Describe the relationship between gas pressure and volume in a mathematical equation.
  • Use the results to predict the pressure at other volumes.

Figure 1

MATERIALS

LabQuest / Vernier Gas Pressure Sensor
LabQuest App / 20 mL gas syringe

PROCEDURE

1.Prepare the Gas Pressure Sensor and an air sample for data collection.

  1. Connect the Gas Pressure Sensor to LabQuest and choose New from the File menu. If you have an older sensor that does not auto-ID, manually set up the sensor.
  2. With the 20 mL syringe disconnected from the Gas Pressure Sensor, move the piston of the syringe until the front edge of the inside black ring (indicated by the arrow in Figure 1) is positioned at the 10.0 mL mark.
  3. Attach the 20 mL syringe to the valve of the Gas Pressure Sensor.

2.Set up the data-collection mode.

  1. On the Meter screen, tap Mode. Change the mode to Events with Entry.
  2. Enter the Name (Volume) and Units (mL). Select OK.

3.To obtain the best data possible, you will need to correct the volume readings from the syringe. Look at the syringe; its scale reports its own internal volume. However, that volume is not the total volume of trapped air in your system since there is a little bit of space inside the pressure sensor.

To account for the extra volume in the system, you will need to add 0.8 mL to your syringe readings. For example, with a 5.0 mL syringe volume, the total volume would be 5.8 mL. It is this total volume that you will need for the analysis.

4.You are now ready to collect pressure and volume data. It is easiest if one person takes care of the gas syringe and another enters volumes.

  1. Start data collection.
  2. Move the piston so the front edge of the inside black ring (see Figure 2) is positioned at the 5.0 mL line on the syringe. Hold the piston firmly in this position until the pressure value displayed on the screen stabilizes.
  3. Tap Keep and enter 5.8, the gas volume (in mL) on the screen. Remember, you are adding 0.8 mL to the volume of the syringe for the total volume. Select OK to store this pressure-volume data pair.

Figure 2

  1. Continue this procedure using syringe volumes of 10.0, 12.5, 15.0, 17.5, and 20.0 mL.
  1. Stop data collection.

5.When data collection is complete, a graph of pressure vs. volume will be displayed. To examine the data pairs on the displayed graph, tap any data point. As you tap each data point, the pressure and volume values are displayed to the right of the graph. Record the pressure and volume data values in your data table.

6.Based on the graph of pressure vs. volume, decide what kind of mathematical relationship exists between these two variables, direct or inverse. To see if you made the right choice:

  1. Choose Curve Fit from the Analyze menu.
  2. Select Power as the Fit Equation. The curve fit statistics for these two data columns are displayed for the equation in the form

y = Ax^B

where x is volume, y is pressure, A is a proportionality constant, and B is the exponent of x (volume) in this equation. Note: The relationship between pressure and volume can be determined from the value and sign of the exponent, B.

  1. If you have correctly determined the mathematical relationship, the regression line should very nearly fit the points on the graph (that is, pass through or near the plotted points).
  2. Select OK.

7.(optional) If directed by your instructor, proceed directly to the Extension that follows Processing the Data.

DATA and calculations

Volume
(mL) / Pressure
(kPa) / Constant, k
(P/V or P•V)

Processing the data

1.If the volume is doubled from 5.0 mL to 10.0 mL, what does your data show happens to the pressure? Show the pressure values in your answer.

2.If the volume is halved from 20.0 mL to 10.0 mL, what does your data show happens to the pressure? Show the pressure values in your answer.

3.If the volume is tripled from 5.0 mL to 15.0 mL, what does your data show happened to the pressure? Show the pressure values in your answer.

4.From your answers to the first three questions and the shape of the curve in the plot of pressure versus volume, do you think the relationship between the pressure and volume of a confined gas is direct or inverse? Explain your answer.

5.Based on your data, what would you expect the pressure to be if the volume of the syringe was increased to 40.0 mL. Explain or show work to support your answer.

6.Based on your data, what would you expect the pressure to be if the volume of the syringe was decreased to 2.5 mL.

7.What experimental factors are assumed to be constant in this experiment?

8.One way to determine if a relationship is inverse or direct is to find a proportionality constant, k, from the data. If this relationship is direct, k = P/V. If it is inverse, k = P•V. Based on your answer to Question 4, choose one of these formulas and calculate k for the seven ordered pairs in your data table (divide or multiply the P and V values). Show the answers in the third column of the Data and Calculations table.

9.How constant were the values for k you obtained in Question 8? Good data may show some minor variation, but the values for k should be relatively constant.

10.Using P, V, and k, write an equation representing Boyle’s law. Write a verbal statement that correctly expresses Boyle’s law.

Extension

1.To confirm that an inverse relationship exists between pressure and volume, a graph of pressure vs.reciprocal of volume (1/volume) may also be plotted. To do this using LabQuest:

  1. Tap the Table tab to display the data table.
  2. Choose New Calculated Column from the Table menu.
  3. Enter the Name (1/Volume) and Units (1/mL). Select the equation, A/X. Use Volume as the Column for X, and 1 as the value for A.
  4. Select OK.

2.Follow this procedure to calculate regression statistics and to plot a best-fit regression line on your graph of pressure vs. 1/volume:

  1. Choose Graph Options from the Graph menu.
  2. Select Autoscale from 0 and select OK.
  3. Choose Curve Fit from the Analyze menu.
  4. Select Linear as the Fit Equation. The linear-regression statistics for these two data columns are displayed in the form:

y = mx + b

where x is 1/volume, y is pressure, m is a proportionality constant, and b is the y-intercept.

  1. Select OK. If the relationship between P and V is an inverse relationship, the graph of pressure vs. 1/volume should be direct; that is, the curve should be linear and pass through (or near) the origin. Examine your graph to see if this is true for your data.

Charles’ Law Lab

Purpose: To determine the relationship between Temperature and volume of a gas.

Procedure

  1. Obtain an empty 250 mL Erlenmeyer flask with a one hole stopper and use crucible tongs to hold it in a boiling how water bath.
  2. After 5 min quickly invert the flask (holding your finger over the one hole) and move it into a vat of ice cold water.
  3. Remove your finger from the stopper and allow water to move into the flask.
  4. Hold the flask under the water for 5 minutes
  5. Measure the amount of water in the flask using a graduated cylinder
  6. Measure the total amount of water in the flask using a graduated cylinder.
  7. Measure the temperature of both the ice water and the boiling water.

Safety

There is a danger of the flask imploding. You need to make sure that your flask has no chips or cracks. If so report this to your teacher immediately and don’t use that flask.

Data

Total Volume of water in flask
Volume of water in flask after the experiment
Volume of air in the flask when hot
Volume of air in the flask when cold
Temperature of the hot gas (˚C)
Temperature of the cold gas (˚C)

Data Analysis

Plot a graph of temperature (x axis) verses Volume (y axis). Set your such that the temperature goes from –400˚C to 200˚C. Set your volume (y axis) to be from 0 to 300 mL

Place two points on your graph and draw the line back to where volume is equal to zero.

Questions

  1. At what point did your line cross the x axis? What is the significance of this point?
  2. What happens to molecules at absolute zero?
  3. What would really happen to your gas if you cooled it down to a really low temperature? (HINT: Think about attractive forces)
  4. What is your percentage error for the determination of absolute zero?

Stoichiometry and Gas Law Lab

Purpose: To determine the volume of H2 that will be liberated when a sample of magnesium is completely reacted with excess hydrochloric acid (HCl). This is a single replacement reaction.

Material: Magnesium ribbon--untarnished, thread, hydrochloric acid--concentrated.

Procedure:

Fill a plastic tub with water. Roll a length of magnesium ribbon of known mass into a loose coil. Tie it with one end of a piece of thread, approx 25 cm. in length, in such manner that all the loops of

coil are tied together. Obtain 5ml. of concentrated hydrochloric acid (DANGER) from your instructor in the eudiometer. Slowly fill it completely with water, being careful not to mix the water and the acid. Lower the magnesium coil into the water in the gas measuring tube to a depth of about 5 cm. Close the tube with your thumb so that the thread is held firmly against the edge of the tube. Taking care that no air enters, invert the eudiometer in the tub and allow it to rest against the bottom to hold the thread. It may be clamped in this position on the ring stand, as shown.

When the magnesium has completely reacted (no more metal present and the bubbles have stopped), go to the big bucket of water and insert your tube in the water. Adjust the tube until the liquid levels inside and outside are the same. Read the volume of hydrogen gas liberated as precisely as possible. Take the temperature of the water in the tub and assume this to be temperature of the hydrogen gas collected. Record the barometric pressure from the board.

Procedure:

Turn the paragraphs above into a stepwise procedure. Place an * next to each step whenever a measurement must be recorded in your data table,

Data & Calculations:

  1. Record all data in the provided table.
  2. The mass of one meter of magnesium is ______. Determine the mass of your sample.
  3. Calculate the expected volume of hydrogen gas from your data. Begin with the balanced equation and use the ideal gas law to determine the volume of H2 that should have been collected from the mass of magnesium you started with.
  4. Calculate the % error using the calculated volume from question (2) above as the accepted value and your measured volume as the experimental value.

Questions:

1. What type of reaction occurred? (single, double, synthesis, decomposition, combustion)

2. Why is it necessary to make a water-vapor correction of the barometer reading in this experiment?

3. If this same experiment were done in Florida, how would the experimental volume (would it be higher or lower) of the gas have changed? Explain thoroughly.

4. Complete a cause-effect error analysis to explain your observed % error. Include a minimum of 4 specific errors.

Data Table

Length of Mg obtained (cm)
Mass of Mg (g)
Volume of H2 Actual (mL)
Temperature of H2O=THydrogen
Atmospheric Pressure (mmHg)
Vapor Pressure of H2O (mmHg)
Pressure of H2
Volume of H2 Predicted (mL)
Percentage Error

CUT THIS TABLE OUT AND PLACE IT IN YOUR COMPOSITION BOOK

Water Vapor Pressure

Temp ºC / VP
mm Hg / Temp ºC / VP
mm Hg
4 / 6.1 / 27 / 26.7
5 / 6.5 / 28 / 28.3
6 / 7.0 / 29 / 30.0
7 / 7.5 / 30 / 31.8
8 / 8.0 / 31 / 33.6
9 / 8.6 / 32 / 35.6
10 / 9.2 / 33 / 37.7
11 / 9.8 / 34 / 39.8
12 / 10.5 / 35 / 42.1
13 / 11.2 / 36 / 44.5
14 / 12.0 / 37 / 47.0
15 / 12.8 / 38 / 49.7
16 / 13.6 / 39 / 52.4
17 / 14.5 / 40 / 55.3
18 / 15.5 / 41 / 58.3
19 / 16.5 / 42 / 61.5
20 / 17.5 / 43 / 64.8
21 / 18.6 / 44 / 68.3
22 / 19.8 / 45 / 71.9
23 / 21.0 / 46 / 75.6
24 / 22.3 / 47 / 79.6
25 / 23.7 / 48 / 83.7
26 / 25.2 / 49 / 88.0

Gas Laws Worksheet 7.2: Boyles-Charles-Gay-Lussac

1. You are now wearing scuba gear and swimming under water at a depth of 66.0 ft. You are breathing air at 3.00 atm and your lung volume is 10.0 L. Your scuba gauge indicates that your air supply is low so, to conserve air, you make a terrible and fatal mistake: you hold your breath while you surface. What happens to your lungs? Why?

2. A gas with a volume of 4.0 L at a pressure of 0.90-atm is allowed to expand until the pressure drops to 0.20-atm. What is the new volume?

3. A given mass of air has a volume of 6.0 L at 1.0-atm. What volume will it occupy at 190 mm Hg if the temperature does not change?

4. The pressure of air in an automobile tire is 2.0-atm at 27˚ C. At the end of a journey on a hot sunny day the pressure has risen to 2.2-atm. What is the temperature of the air in the tire? (Assume that the volume of the tire has not changed.)

5. Five liters of air at -50˚C is warmed to 100˚C. What is the new volume if the pressure remains constant?

6. A gas cylinder contains nitrogen gas at 10-atm pressure and a temperature of 20˚C. The cylinder is left in the sun, and the temperature of the gas increases to 50˚C. What is the pressure in the cylinder?

7. A bike tire has a volume of 0.850L at a pressure of 40 psi and 0˚C. What will be the pressure of the tire at 35˚C?