PURPOSE: to Give the Student a Better Understanding of Boyle's Law Through Manipulation

Boyles Law

PURPOSE: To give the student a better understanding of Boyle's Law through manipulation of lab equipment and graphic display of gathered data. INTRODUCTION: During the 17th century, Robert Boyle conducted a series of experiments that led him to the theory behind Boyle's Law. This law states that the volume and pressure of a gas are inversely proportional and when multiplied, equal to a constant. PV = k That is, when the pressure of a gas goes up, the volume goes down, and vice versa. In order for this to be true the temperature of the gas must remain constant. This can be illustrated by the equation:

V1 P1 = k V2 P2 = k thus V1 P1 = V2 P2 Where the subscripts 1 and 2 represent the first and second set of conditions respectfully. If three of these variables are known, we can solve for the fourth:

V2 = V1 P1 / P2 Volume (V) is typically measured in mL or L while pressure (P) can be measured in a variety of units such as atmospheres (atm), millimeters (mm) or kilopascals (kPa). Conversion factors for these units are: 1 atm = 760 mm = 101.3 kPa Pressure is defined as Force per Area or P = F / area Force is defined as mass, in kg, times acceleration (gravity) in m/s2. F = mass gravity The units for F are kg m/s2 or Newtons (N). If area is measured in m2 then the units for P are N/m2 or Pascals (Pa). From all of this, if we know the mass of an object and the area it is pressing down upon, we can calculate the Pressure it is exerting. ---*---

On your table you will find a syringe. This will serve as a container for the gas that will be used during the lab. The plunger can be pulled in and out to change its initial volume. Once placed in its holder, the end of the syringe seals against a rubber stopper and the gas can no longer escape.

---*--- The syringe must be supported in order to serve as a platform for any added mass. This holder is a wire apparatus that seals the syringe and keeps the syringe upright.

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The mass that will supply the added pressure, with the help of gravity, takes the form of several text books. Five different editions are used and five different masses will be noted. These books are very heavy due to the numerous pages holding essential information.

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The room pressure will be read from a standard laboratory barometer. This classic device uses mercury to measure the rooms pressure in mm. Although mercury is not normally allowed in the classroom, this device uses a steel jacket to protect the mercury and is considered totally safe.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

---*--- PROCEDURE: 1) Go to: http://eduweblabs.com/TOC/GenChem/GenChem.html and Choose the Boyles Law Lab (see screen shot below). Login using your first name, last name and:  Student ID: use your first and last intial (e.g. John Smith use “JS”)  Teacher last name: slider  School abv: aiss  Class password: student6 You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Select the starting volume of your gas by dragging the plunger of the plastic syringe, lying on the table top. Any value above 50 mL will do. Record this initial gas volume. The area of the syringe plunger is 0.001225 m2. This is actually 12.25 cm2, but we will need this value in m2 at a later time. Keep this value in mind! 2) Read the barometer in the upper left hand corner and record the room pressure. Note that most lab barometers measure in mm, or sometimes cm. Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted) 3) Drag the syringe to a position above and centered to the holding stand and release. The syringe should stay in an upright position within the stand. The end of the syringe is now sealed within the rubber stopper, at the base of the stand, and will not allow you to change its volume by moving the plunger. 4) Place the first book on the scale to the left and record its mass. Now place the book on the syringe top. Notice that the volume of the syringe decreased. Record this new volume. 5) Repeat step 4 for books 2 through 5 and record their mass and new volume. You can have a list presented of all of the volume/mass points that are generated during the lab by clicking on the "Special" button and selecting "View Data & Hints" at the end of the lab. 6) Notice that a representative, not accurate, graph has been constructed at the top of the page for reference. 7) Plot your data points using the X axis as pressure in kPa and the Y axis as volume in mL. Answer any questions asked by your teacher. Click on the "Special" button and select "View Data & Hints" for help on completing the graph and calculating the answers requested on the "Lab Report". Select "File Report" to send a copy to be viewed by your teacher. Hand in your report to your teacher.