Expt 026 -- Boyle's Law
Description
When the pressure is increased on a sample of gas maintained at constant temperature, the volume of the gas decreases. Using a small sample of gas trapped in a sealed insulin syringe, a quantitative study of this relationship is made.
Safety
Exercise extreme caution in dealing with the needles on the insulin syringes -- they are very sharp and can cause injury. Keep needles covered with clay or soft stopper at all times. Topless soda cans can cause cuts; be careful when handling them. Wear goggles and apron.
Procedure
- In the center of one cardboard square make a hole large enough to accommodate the barrel of the syringe.
- !!!Click here to See Picture.
- Secure one ring on the support stand at a convenient viewing height. Move the piston in the syringe to the 1 mL (0.5 mL for the smaller size) setting. Carefully place the syringe through the small hole in one cardboard square. Remove the needle protector and insert the needle into the soft rubber stopper (or some modeling clay).
- !!!Click here to See Picture.
- !!!Click here to See Movie.
- Set this assembly on the center of the lower ring. Place the second ring about 10 cm above the first ring.
- In the center of the second cardboard square cut a hole large enough for the beverage can to move up and down freely but not flop from side to side. below.
- The can should be 100 g before starting to keep it from sticking initially. A weight was sealed in wax to add initial mass to the can used here.
- !!!Click here to See Picture.
- Measure the mass of the empty beverage can. (It should be preweighed to 100 g.)
- !!!Click here to See Picture.
- Place the remaining cardboard square on the top ring and pass the can through the hole and rest the center of the can on the top of the piston.
- !!!Click here to See Picture.
- Press down on the can to force the plunger of the syringe down and then release.
- Record the mass of the can; record the volume of the syringe. (Do not use the data point for 0 mass and either 0.5 mL or 1.0 mL.)
- Add water to the can in 50 mL increments.
- !!!Click here to See Movie.
- Record the mass and the volume each time.
- !!!Click here to See Movie.
- !!!Click here to See Picture.
- Continue the procedure until the total mass is 550 grams. (550 grams is possible for the specially prepared tall form cans.)
- Disassemble the equipment carefully according to the instructor's instructions.
- Prepare two graphs of the data. On the first, graph the volume on the x-axis and pressure (mass) on the y-axis. On the second graph, plot 1/volume on the x-axis and the pressure (mass) on the y-axis.
Questions
- Summarize the principal finding of this experiment.
- Suppose a gas sample has a pressure of 760 mm Hg and a volume of 68 mL. Predict the volume when the pressure is reduced to 380 mm Hg at constant temperature.
- Suggest ways to determine whether the relationship between pressure and volume depends upon the nature of the gas studied.
Handout Makeup
Name ___________________________ Class ________
Teacher__________________________
SmallScale 026 Boyle's Law
|
Balance Mass
|
Syringe Reading
|
|
100
|
30
|
|
150
|
23
|
|
200
|
18
|
|
250
|
15
|
|
300
|
13
|
|
350
|
11
|
|
400
|
10
|
|
450
|
9
|
|
500
|
8
|
|
550
|
7
|
Use this data for your calculations.
Prepare two graphs of the data. On the first, graph the volume on the x-axis and pressure (mass) on the y-axis. On the second graph, plot 1/volume on the x-axis and the pressure (mass) on the y-axis.
Answer the questions.
Curriculum-
Use when studying the quantitative relationships of gases. This also is an experiment that involves data analysis.
Safety-
- Exercise extreme caution in dealing with the needles on the insulin syringes -- they are very sharp and can cause injury. Keep needles covered with clay or soft stopper at all times. Only the teacher should handle syringes while the needles are exposed. This usually means setting the syringes into the cardboard support frames, pulling the plungers nearly out of the barrels, and then inserting the needles into clay or stoppers.
- Wear goggles and apron.
- Topless soda cans can cause cuts; be careful when handling them. Use pliers to crimp sharp edges. Cover crimped edges with electrical tape.
Time-
Teacher Preparation: 15 minutes (Preparing cans the first time will require more time.)
Class Time: 40 minutes
Materials-
- 0.5 mL or 1-mL Insulin syringe
- soft rubber stopper
- 450-mL aluminum beverage can with top removed
- support stand
- medium rings for support stand
- cardboard squares, larger than the rings
- 50-mL graduated cylinder
- balance (unless starting mass of cans is set to 100 g).
Disposal-
All materials used in the experiment are saved. Discard water at the sink.
Lab Hints-
- Use tall form cans -- 16 ounce cans, if available. Sometimes a canning factory will provide cans as blanks, open at the top before they are sealed. Fill the bottom of the can with a dense metal and some paraffin until the total mass (ca, added weight, paraffin) is 100 grams. Heat in hot water to melt the paraffin. Cool. This has the effect of making a permanent weight in the can for use in this experiment.
- If ordinary aluminum beverage cans are used, be careful removing the top. A standard can opener will not work since the top sets well below the rim of the can. The top can be removed by carefully cutting around the inside rim with a sharp heavy duty cutting knife. Tape around the sharp lip which remains inside the can to prevent cuts. The depression at the bottom of the can helps keep the force centered over the plunger.
- Moisten the inside plungers with a very small amount of very light lubricating oil.
- Remove most of each needle with metal cutters when clay is used as the closing mechanism. This will minimize the chance of a puncture injury resulting from an accidental stabbing with the needle. If stoppers are used to seal the barrel, the instructor should pull the plunger to near the end of the barrel (past the calibrations), put the syringe through the cardboard support, and insert the needle into the stopper. Don't permit students to use the syringes while syringe needles are exposed.
- Avoid spilling water on the top cardboard support; the wet cardboard expands and causes friction.
- Although mass is plotted, the actual units should be units of pressure. Pressure is force divided by area. Force (due to gravity) is given by mass times acceleration due to gravity.
Data Table-
|
Balance Mass
|
Syringe Reading
|
|
100
|
30
|
|
150
|
23
|
|
200
|
18
|
|
250
|
15
|
|
300
|
13
|
|
350
|
11
|
|
400
|
10
|
|
450
|
9
|
|
500
|
8
|
|
550
|
7
|
Data Analysis-
See the computer-generated graphs below.
Answers-
- Q1. Summarize the principal finding of this experiment.
- A1. The pressure of the gas times the volume of the gas is a constant, or PV = k.
- Q2. Suppose a gas sample has a pressure of 760 mm Hg and a volume of 68 mL. Predict the volume when the pressure is reduced to 380 mm Hg at constant temperature.
- A2. P1V1 = P2V2
- V2 = V1 {P1/P2} = 68 {760/380} = 136 mL = 1.4 x 102 mL
- Q3. Suggest ways to determine whether the relationship between pressure and volume depends upon the nature of the gas studied.
- A3. Using procedures described in other activities, fill the syringe with different gases other than air and repeat the experiment.
Computer Use-
The data are readily analyzed using a graphing program. The graphs shown above were created using DeltaGraph® Professional.
CoopLearn-
Averaging of the data between groups of experimenters gives a better impression of the errors involved in this experiment.
Reference-
The small scale version of this lesson was developed by Jared Ketner, Wahoo, NE. It was developed at an EESA workshop at Lincoln East HS, Lincoln, NE, in 1988. Enhancements were made by Edward Lyons, Lincoln, NE.
Key Words 1-
gases, gas laws, Boyle's law, pressure, volume, ideal gas, compression, balance