Properties of Gases and the Gas Laws
ActivityStations Kit
Materials Included In Kit
Activity A. Diffustion of Gases Ammonium hydroxide solution, NH_{4}OH, 6 M, 20 mL Phenolphthalein indicator solution, 15 mL Petri dishes, disposable, divided, 10 Pipets, Beraltype, graduated, 30 Activity B. Crush the Can Aluminum pie pans, 2
Activity C. Boyle’s Law in a Bottle Petroleum jelly, Foilpac, 5 g Pressure bottles, 1L, with tire valve, 2 Syringes, 10mL, with syringe tip caps, 2 Activity D. Charles’s Law—Effect of Temperature on the Volume of a Gas Petroleum jelly, Foilpac, 5 g Syringes, 30mL, with syringe tip caps, 2 Wood splints
Additional Materials Required
(for each lab station) Activity A. Diffustion of Gases Water, distilled Paper, white Wash bottle Activity B. Crush the Can Water, tap Beaker tongs Graduated cylinder, 25mL “HOT” sign for hot plate Hot plate Soda can, 12oz, aluminum, empty Activity C. Boyle’s Law in a Bottle Barometer (optional)
Bicycle pump with pressure gauge, 2 or electric air pump Graph paper or computer graphing program Tire gauge (optional) Activity D. Charles’s Law—Effect of Temperature on the Volume of a Gas Beakers, 600mL, 3 “HOT” sign for hot plate Hot plate Hot water Hot water bath, 60 to 65 ºC, 400mL Ice Ice water bath, 0 to –5 ºC, 400mL Salt–ice water bath, –15 to –20 ºC, 400mL Stirring rods, large, 3 Thermometer, –20 to 100 ºC
Prelab Preparation
Activity D. Charles’s Law—Effect of Temperature on the Volume of a Gas
Water Baths: Prepare water baths at different temperatures as follows:
 Add crushed ice and a small amount of water (total volume 259 mL) to a 400mL beaker, followed by about 10 scoopfuls of salt to prepare a bath between –10 to 15 ºC.
 Add crushed ice and water to a 400mL beaker for a bath at about 0 ºC.
 Add 250 mL of water to a 400mL beaker and heat it on a hot plate on a low setting to prepare a hot water bath at around 60 to 65 ºC.
 Instruct students to add hot water or ice as needed during the course of the experiment to maintain the temperature of each bath within ±5 ºC of the desired temperature.
Safety Precautions
Ammonium hydroxide solution is toxic by ingestion and inhalation and is corrosive to body tissue. Phenolphthalein is an alcoholbased solution and is flammable. Hot objects and escaping steam can cause severe burns. Handle hot objects with beaker tongs and do not place your hands in the steam. The pressure bottle is safe if used properly. The bottle should not be inflated above 60–80 psi. At very high pressures, the bottle might split, but will not shatter. Wear chemical splash goggles whenever working with chemicals, heat or glassware in the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash hands with soap and water before leaving the lab.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Excess ammonia solution may be neutralized for disposal according to Flinn Suggested Disposal Method #10. Excess phenolphthalein may be disposed of according to Flinn Suggested Disposal Method #18b.
Lab Hints
 For best results, set up two stations for each activity throughout the lab. This will allow eight groups of students to rotate through four activity stations in a 50minute lab period, if needed. A double lab period (two 50minute class periods) will allow time both for a review of basic gas laws before lab and for a collaborative class discussion after lab.
 The activities may be completed in any order. Also, since each activity is a selfcontained unit, the experiment may be set up with as many or as few of the activities as the teacher desires. Students should need only 7–8 minutes per station—keep the pace fairly brisk to avoid dawdling. Questions in the Calculations and Analysis section may be answered during downtime between stations.
 Prelab preparation is an essential component of lab safety, and it is also critical for success in the lab. (Standing in front of the lab station is not a good time for students to be reading the activity for the first time.) Having students complete the written prelab assignment for this lab will help teachers ensure that students are prepared for and can work safely in the lab.
 In Activity A, the indicator color change provides a visual reminder how quickly toxic gases can travel. Since many gases cannot be smelled or seen, this activity reinforces two important safety practices—work in a well ventilated room, and carry out any reactions that may produce toxic fumes in a fume hood.
 In Activity C, if the bottle leaks air around the cap when pressurized, remove the cap assembly and put additional petroleum jelly around the inside seal of the cap.
 The best results in the Boyle’s Law activity are obtained using a bicycle pump with an attached pressure gauge. If one cannot be obtained with student help, the experiment can be done using common automobile tire gauges. Tire gauges come in many shapes and sizes. The best gauges for this activity are those with an attached pressure dial or digital readout rather than a “popout” sliding scale. The units shown on some pressure gauges may be psig (gauge pressure per square inch).
 Students may need instruction in how to use a tire gauge. The pressure scale on a tire gauge is marked in units of pounds per square inch (psi). The scale starts at zero when the gauge is exposed to the surrounding air. This means that the total pressure is equal to the gauge pressure plus the pressure of the surrounding air.
 For best results, use a barometer to measure the local barometric pressure. The National Weather Service website reports corrected sealevel air pressures. Note that these are not actual barometric pressure readings. Meteorologists convert station pressure values to what they would be had they been taken at sealevel. The following equation can be used to recalculate the barometric pressure (in inches Hg) from the reported sealevel pressure (in inches Hg). Elevation, which must be in meters, can be obtained from geological survey sites.
Barometric pressure = sealevel pressure – (elevation/312 m)
On the syringes, the black rubber seals have two “seal lines.” Make sure students are consistent in where they measure the volume!
 In Activity D, teachers who have access to computerbased graphing programs may want to schedule additional time for students to graph and analyze their data. The graphs will be more precise than handdrawn graphs and allow students to obtain more accurate estimates of absolute zero. The actual temperatures of the water baths are not important as long as students measure volumes over a wide enough temperature range. The difference between any two baths should be at least 15–20 ºC.
Teacher Tips
 Many students have bicycle pumps or tire gauges they are willing to loan to the classroom for a short time in the interest of science (and of course, extra credit). Ask your students for assistance. Electric air pumps are common items in vocational education or mechanical arts classrooms. If using an electric pump, the teacher should inflate the pressure bottles ahead of time for each group. The students may then use tire gauges to measure the pressure.
 Activity A is a modification of the Graham’s law demonstration that uses hydrochloric acid and ammonium hydroxide to produce a visible cloud of ammonium chloride (NH_{4}Cl) particles. This activity uses one gas and a stationary indicator. Phenolphthalein is an acid–base indicator and turns red when exposed to a base. “Ammonium hydroxide” is a concentrated solution of ammonia gas and water. Ammonia is a base and very volatile.
 What does a pressure of 14.7 psi feel like? The “Atmosphere Bar” available from Flinn Scientific (AP5882) is a 52inch steel bar that weighs 14.7 lbs., with a base of one inch square.
 In Activity C, do not exceed the maximum pressure recommended in the Procedure section. It was found that the graph of P versus 1/V became nonlinear as the pressure bottle was pressurized above about 70 psi (total pressure 85 psi). This can be used as a teaching point—deviations from ideal gas behavior are more important at higher pressures. Many textbooks show graphs of real versus ideal gas behavior as a function of pressure. For many gases, deviations from ideal behavior become significant at pressures greater than about 200 psi. Even at modest pressures, however, small deviations are common in the P x V “constant.” Some of this deviation may also be due to a change in temperature. Compressing the gas will increase the temperature of the gas.
 Jacques Charles was at least partially inspired by his interest in hotair ballooning to study the properties of gases. If it worked for him, it may work for your students as well! Inspire your students to learn more about the properties of gases with the hotair balloon activity kit “Up, Up and Away” (Flinn Catalog No. AP6310). The kit contains enough materials for 15 pairs of students to construct and launch their own giant hotair balloon. Students will learn how hotair balloons lift from the ground, stay aloft, and eventually descend. The volume of a gas is always proportional to temperature. It is directly proportional, however, only to the absolute temperature. Thus, in gas law calculations temperature must always be reported in kelvins.
Correlation to Next Generation Science Standards (NGSS)^{†}
Science & Engineering Practices
Developing and using models Analyzing and interpreting data Planning and carrying out investigations
Disciplinary Core Ideas
MSPS1.A: Structure and Properties of Matter MSPS1.B: Chemical Reactions MSPS3.A: Definitions of Energy MSPS3.B: Conservation of Energy and Energy Transfer HSPS1.A: Structure and Properties of Matter
Crosscutting Concepts
Cause and effect Patterns Scale, proportion, and quantity
Performance Expectations
MSPS12. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. MSPS14. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed. MSPS34. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample. HSPS13. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Answers to Prelab Questions
In Activity A, the ability of gas molecules to diffuse will be studied by observing the reaction of ammonia with phenolphthalein, an acid–base indicator.
In Activity B, the force exerted by the atmosphere will be studied by observing its effect on a partially evacuated soda can.
In Activity C, the relationship between the volume and pressure of a gas will be determined by performing a new version of Boyle’s experiment, using a syringe and a pressurized soda bottle. As the pressure in the bottle is varied, the changes in the volume of the air in the syringe will be measured. Graphing of these two variables will yield their relationship.
In Activity D, the relationship between the volume and temperature of a gas (Charles’ law) will be discovered by measuring the volume of air in a sealed syringe at four different temperatures. The syringe will be placed in different water baths at –15 °C, 0 °C and 55 °C. As the syringe is placed in each bath, the changes in the volume of the air in the syringe will be measured. Graphing of these two variables will yield their relationship.
Sample Data
Activity A. Diffusion of Gases
Observations and Analysis
 Describe the initial color and appearance of each solution and any changes that were observed when the Petri dish was covered.
Initially, both solutions are clear. When the Petri dish is covered, the phenolphthalein solution turns a hot pink or bright red within minutes.
 What compound was responsible for the color change observed in the phenolphthalein solution? Assuming that none of the liquids was spilled or contacted each other in any other way, how did this compound “travel” to the indicator?
Ammonia, NH_{3}, a weak base, is responsible for the color change. Ammonia volatilizes from the ammonium hydroxide solution and subsequently dissolves in the phenolphthalein solution.
 What is the role of the phenolphthalein “indicator” in this demonstration? Write an equation for the reaction of ammonia gas with water that explains the indicator color change.
The indicator color change shows visually how quickly gases can travel.
NH_{3}(g) + H_{2}O(l) → NH_{4}^{+}(aq) + OH^{–}(aq)
 What evidence does this demonstration provide that gas molecules are moving continuously about and randomly colliding with nearby walls and surfaces?
Since the two solutions are physically separated from each other, the only way for the gas molecules to dissolve in the phenolphthalein solution is for the gas molecules to move all through the space above both liquids.
 Describe two observations from daily life that also show us that gas molecules are able to move randomly through a “container.”
Smells coming from the kitchen. Hot air moving into a cold room.
Activity B. Crush the CanObservations and Analysis
 Describe your observations; be specific. What happened when the can was heated? When it was plunged into the water bath?
The pop can was filled with water, then heated for several minutes to boil the water and produce steam. Once steam flowed out of the can, the can was quickly inverted and plunged into a pan of cold water. The sides of the can started to collapse inward.
 What “force” caused the can to collapse inward on itself?
The greater air pressure surrounding the can acted as a force on the outside of the can.
 What “drove” the air out of the can as it was heated?
The steam from the boiling water inside the can.
 Why was there less air pressure inside the can after it was quickly cooled in the water “bath”?
With the air in the can driven out, the can was filled with mostly water vapor. Plunging the can into cold water caused the water vapor to condense. This drastically reduced the pressure inside the can, allowing the much higher air pressure outside to crush the can.
Activity C. Boyle’s Law in a BottleData and Results Table
{12545_Data_Table_1}
*See PostLab Calculation 2. †See PostLab Calculation 5.
Activity D. Charles’s Law—Effect of Temperature on the Volume of a GasData and Results Table
{12545_Data_Table_2}
Answers to Questions
Activity C. Boyle’s Law in a Bottle
 Convert the local barometric pressure to psi units and enter the value to the nearest psi in the Data and Results Table. 1 atm = 760 mm Hg = 29.92 in Hg = 14.7 psi.
{12545_Data_Equation_1}
 The tire pressure gauge measures the relative pressure in psi above atmospheric pressure. For each pressure reading in the Data and Results Table, add the local barometric pressure in psi to the gauge pressure to determine the total pressure of air in psi inside the pressure bottle. Record the total pressure in the table.
Sample calculation for trial 1: Total pressure = 42 psi + 15 psi = 57 psi Refer to the Data and Results Table for the results of other calculations.
 Identify the independent and the dependent variables in this experiment.
The independent variable is pressure and the dependent variable is volume.
 Plot a graph of the dependent variable on the yaxis versus the independent variable on the xaxis. Choose a suitable scale for each axis so that the data points fill the graph as completely as possible. Remember to label each axis (including units) and to give the graph a title.
{12545_Data_Figure_3}
 Describe the shape of the graph. Draw a bestfit straight line or curve, whichever seems appropriate, to illustrate how the volume of a gas changes as the pressure is varied.
The graph is curved. The volume decreases as the pressure increases. At first, there is a sharp reduction in the volume as the pressure increases. The decrease in volume then becomes more gradual and the volume appears to level off as the pressure increases further. Mathematically, the shape of the curve is described as hyperbolic. A hyperbolic curve of this type is obtained when there is an inverse relationship between two variables (e.g., y = 7/x). See the graph for the bestfit curved line through the data.
 The relationship between pressure and volume is called an inverse relationship—the volume of air trapped inside the syringe decreases as the pressure increases. This relationship may be expressed mathematically as P ∝ 1/V. Calculate the value of 1/V for each volume measurement and enter the results in the table.
Sample calculation for trial 1: V = 2.0 mL 1/V = 0.50 mL^{–1} Refer to the Sample Data and Results Table for the results of the other calculations.
 Plot a graph of pressure on the yaxis versus 1/V on the xaxis and draw a bestfit straight line through the data points. Choose a suitable scale for each axis. Remember to label each axis and to give the graph a title.
{12545_Data_Figure_4}
 Another way of expressing an inverse relationship between two variables (P ∝ 1/V) is to say that the mathematical product of the two variables is a constant. (P x V = constant). Multiply the total pressure times the volume for each set of data points. Calculate the average value of the P x V “constant” and the average deviation. (Rounded to two significant figures.)
{12545_Data_Table_3}
Activity D. Charles’s Law—Effect of Temperature on the Volume of a Gas
 Identify the independent and the dependent variables in this experiment.
Temperature is the independent variable and volume is the dependent variable.
 Plot a graph of the dependent variable on the yaxis versus the independent variable on the xaxis. Choose a suitable scale for each axis so that the data points fill the graph as completely as possible. Remember to label each axis, including the units, and to give the graph a title.
{12545_Answers_Figure_5}
 Draw a bestfit straight line through the data points on the graph. Describe the mathematical relationship between the temperature and volume of a gas.
A straight line graph implies that the volume of a gas is directly proportional to its temperature.
 For each of the three temperatures in this experiment, calculate the value of the volume/temperature (in °C) ratio. How do these ratios compare with one another?
Calculation for trial 1: V = 13.6 mL, T = –14 ºC V/T (ºC) = –0.97 mL/ºC Refer to the Sample Data and Results Table for the results of the other calculations. Numbers vary widely. At 0 ºC no number can be determined.
 Convert each of the temperature readings in this experiment to absolute temperature (kelvins, K).
Calculation for trial 1: T ºC = –14 ºC T(K) = T (ºC) + 273.15 = 259 K Refer to the Sample Data and Results Table for the results of the other calculations.
 Calculate the value of the volume/temperature (in K) ratio for each of the four temperatures in this experiment. How do these ratios compare with one another?
Calculation for trial 1: V = 13.6 mL, T = 259 K V/T (ºC) = 5.3 x 10^{–2} mL/K Refer to the Sample Data and Results Table for the results of the other calculations. The ratios are basically constant.
 Which volume/temperature ratio (in °C or K) appears to be more constant? Saying that the ratio of two variables is a constant is to say that the two variables are directly proportional to each other. Why is it important to specify absolute temperature (in K) when stating Charles’s law?
Volume is only directly proportional to temperature in kelvins.
 According to the kineticmolecular theory, the volume of the gas particles is extremely small compared to the volume the gas occupies—most of the volume of gas is “empty space.” Based on this theory, does Charles’s law depend on the identity of the gas? Would the results in this experiment have been different if different gases had been used in the syringe? Or, if the amount of gas in the syringe was different? Explain in terms of the KMT and the amount of empty space in gas.
Since most of the volume of a gas is empty space, the relative size (molecular weight or volume) of a gas particle does not have an appreciable effect on the overall volume of the gas sample. The results using a different gas would be identical.
References
Special thanks to Patricia Mason (retired) Delphi Community H.S., Delphi, IN, and to Kathy Kitzmann, Mercy H.S. Farmington Hills, MI, for providing Flinn Scientific with general ideas and specific activities for “activity station” lab kits.
