The Ideal Gas Law
PURPOSE:
To give the student a better understanding of the Ideal Gas Law through manipulation of lab equipment, gathering data and mathematical use of numeric values.
INTRODUCTION:
The Ideal Gas Law is a mathematical relationship of volume, temperature, pressure and moles of a gas tied together with the gas law constant . This relationship can be shown as:
pV = nRT
where p = pressure measured in atmospheres, T = temperature measured in Kelvin, n = moles of gas, V = volume measured in Liters and R = the gas constant (0.08206 L atm / mol K). Knowing any combination of 3 of these variables, you can solve for the 4th. The most common use is to solve for V, thus:
V = nRT / p
would be used. Temperature is typically converted from lab conditions in °C to Kelvin by adding 273 to the Celsius value. Pressure is converted from lab conditions in mm to atmospheres by dividing the pressure(in mm) by 760.
This lab centers on the n value of this equation. You will calculate the number of moles of your gas and then using the grams of gas used, determine the atomic mass of your gas. A butane lighter is the source of gas but BEWARE, butane lighters are actually a mixture of several gases and not pure butane. Assuming that your gas is pure butane and stating the atomic mass of your gas to be 58.14 will be a major mistake!
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You will be collecting your gas in a standard graduated cylinder but it will be inverted. You have to remember that the scale is reversed so observe clearly to estimate your volume. A stopper is provided to close off the cylinder when you invert. /---*---
/ The gas will be collected by a water displacement process that requires a source of water. A sink is provided that operates by clicking on the handle.---*---
To house the cylinder and body of water, a plastic battery jar is provided. Notice the small wire rack in the bottom. This rack provides a place to set the graduated cylinder on so gas may enter from underneath. /---*---
/ The gas you will be collecting comes from a butane lighter. The sparker has been removed so accidental ignition is not possible. Fight the urge to let the gas free in the room since an error will occur.---*---
An electric balance is provided to take the required masses. /---*---
/ 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 Ideal Gas 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". Drag the butane lighter and place it on the balance. Record this value. 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)
2) Observe the pressure of the room and Record this value. DO NOT record the temperature at this time since it is currently reading the room temperature and not that of the gas.
3) Place the battery jar under the faucet and fill it three quarters full by clicking on the handle. Return it to the center of the table.
4) Place the graduated cylinder under the faucet and fill it completely full. If it is not completely full, a false reading of your butanes volume will be made later! Place the stopper found on the table on the top of the cylinder. Lift up the cylinder and while in the air press the "P" key. The cylinder has now been inverted and is ready to be dropped into the battery jar. Place it in the battery jar.
5) Drop the thermometer into the battery jar. If you noticed, the thermometer is now reading the temperature of the water. Since you will be collecting a gas that has passed through this water, the temperature of the gas is the same as the water. Record this temperature as the temperature of your gas.
6) Remove the stopper from the graduated cylinder by dragging it to one side. Position the graduated cylinder on the wire rack at the bottom of the battery jar. This allows you to place the lighter under the opening of the cylinder so gas may be captured.
7) Drop the lighter into the battery jar. Position it so the silvered end is directly underneath the opening of the cylinder. Slightly lift the lighter and then press the "P" key. The gas should now escape from the lighter and collect in the cylinder. Collect from 180 mL to 190 mL. Record this value as the volume of butane.
8) Remove the lighter from the battery jar and shake it to remove any water trapped in its top. Place it on the balance and determine the new reduced mass.
9) Calculate the grams of butane used, moles of gas collected and then the atomic mass of your gas. Remember that this is not pure butane. Record these values in your lab data table. Click on the "Special" button and select "View Data & Hints" for help on calculating the answers requested on the "Lab Report". Select "File Report" to send a copy to be viewed by your teacher.