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# Experimental data analysis

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1. Record your data table of temperature vs. volume here.

2. Construct a graph by hand or using a spreadsheet program, plotting the values of temperature on the x-axis and air volume on the y-axis.

Initial temp. 21 Deg C, Vol. 100mL
Ice -3 Deg C, Vol. 91.84mL
Water 100 deg. C, Vol. 126.87mL
Gas Piston Removed: Temp. Deg. C Vol. mL
100 126.87
95 125.31
90 123.48
85 122.11
80 120.21
75 118.39
70 116.58
65 115.08
60 113.31
55 111.66
50 109.91
45 108.21
40 106.49
35 104.76
30 103.08
25 101.37
21 100

3. Draw a straight line through the points.

4. Determine the slope of the line and record its value here. Be sure to include the units for this slope value. If you are using a spreadsheet program, use its built-in function to find the slope of the straight line. In Excel, use the function SLOPE (y-values, x-values).

5. Is the volume of air proportional to its temperature?

Assignment 1 of Procedure 2

1. Record your table of measured data, air volume and pressure in atm. Add a third column for the value of
(1 / pressure), with units of "reciprocal atm" or 1/atm.
Gas Vol. mL Pressure atm Liquid Vol. mL
150.00 1.ooo 0
130.00 1.154 20.00
116.00 1.364 40.00
90.00 1.667 60.00
70.00 2.143 80.00
50.00 3.000 100.00

2. Construct a graph by hand or using a spreadsheet program, plotting the values for (1 / pressure) on
the x-axis and air volume on the y-axis.

3. Draw a straight line through the points.

4. Determine the slope of this line and record its value here. Be sure to include units for this slope value. If you are using a spreadsheet program, use its built-in function to find the slope of the straight line. In Excel, use the function SLOPE (y-values, x-values).

5. Is the volume of air proportional to its "reciprocal pressure", i.e., inversely proportional to its pressure?

Assignment 1 of Procedure 3

1. For this part of the experiment, the temperature is the room temperature of 21C and the pressure is the room pressure of 1 atm. The gas constant, R = 0.08 = 0.082057 (L*atm)/(K*mole), so make sure to convert your temperature value to Kelvin. For each of the 4 total volumes of air, record and calculate the following:
Initial Mass of Gas Piston: 111.420g before 3 more increments of 50 mL of air

(a) the mass of air (g):#1 111.480g
#2 111.540g
#3 111.599g
#4 111.659g
(b) the volume of air (L)
(c) the calculated MW of air (g/mol)

Average the four values for the MW and report it here.

2. If you look up the composition of air, you will find that it is composed of:

N2, 78.084%
O2, 20.947%
Ar, 0.934%
CO2, 0.033%

There are some other gases present, but in very small quantities that do not influence its overall properties. The percentages shown above are by VOLUME.

Given the composition of air, it is possible to calculate a theoretical value for its apparent molecular weight as the weighted average of the individual components. The formula for this is:

MW(air) = (MW(1) * Volume-Percent(1) + MW(2) * Volume-Percent(2) + ...) / (100)

Note that the molecular weight of a component is for the entire molecule of the component, not the individual atom.

Calculate and record the theoretical molecular weight using the four components listed above.

3. How well does the theoretical value for the molecular weight of air compare with your experimentally determined value? Find the percent deviation according to:

% deviation = 100 * (experimental MW - theoretical MW) / (theoretical MW)

4. The molecular weights discussed here are for DRY air, but air often has some water vapor mixed in with it. Would you expect the apparent MW of non-dry air to be less or more than for dry air? Explain.

THIS MAY HELP

Procedure 1

1. This procedure will test the proportionality of volume and temperature for a sample of air.

2. Take a gas piston from the Glassware tab of the Labware Shelf and place it on the Workbench.

3. Fill the piston with 100 mL of air from the air cylinder on the Chemicals Shelf.

4. Take a thermometer from the Tools tab of the Labware Shelf and drop it on the gas piston. On a piece of paper record the first set of data values: room temperature and a volume of 100 mL.

5. Take a constant temperature bath from the Tools shelf and drop it directly onto the gas piston. Let the air inside of the piston cool until it reaches a steady temperature. (The default setting of the constant temperature bath is "ice".)

6. Open the Data window, then click on the gas piston to see the volume inside. Click on the "pushpin" to lock the Data window to the gas piston.

7. Record the temperature and volume of the air inside the gas piston.

8. Open the Properties window, click on the bath and set its temperature to 100C.

9. When the air temperature stabilizes at its highest temperature, record the volume and temperature of the air.

10. Remove the gas piston from the bath and watch it cool down. Record the temperature and volume of the air for every change of temperature of 5C or so.

(Note: Write fast, the temperature drops quickly from 100 Deg C down to 40 Deg C, then more slowly to the lab ambient temperature.)

Procedure 2

1. This procedure will test the inverse proportionality of volume and pressure for a sample of air.

2. Clear the workbench by dragging all tools and glassware to the recycling chute.

3. Take a 150 mL Erlenmeyer flask from the Glassware tab of the Labware Shelf and place it on the Workbench.

4. Open the Properties window, click back on the flask, and close the flask with an airtight stopper.

5. Take a pressure gauge from the Tools tab of the Labware Shelf and drop it on the flask. Click on the pressure gauge and in the Properties window select "atm" as the units of measurement. The pressure gauge should now read 1.000 atm.

6. Open the Data window and click back on the flask. You will see that the primary components of air fill the flask's volume. Record the first set of data as 150 mL and 1.000 atm.

7. Click the pushpin button on the Data window to lock its display to the flask.

8. Add 20.00 mL of water to the flask. (This is added as if injected right through the closed stopper.)

9. Record the gas volume and pressure. The gas volume is the total volume of the flask minus the volume of the water. (This gas volume is displayed in the Data window.)

10. Continue to add water in 20.00 mL increments until the liquid (water) volume reaches 100.00 mL. Record the gas volume and the pressure for each increment of water added.

Procedure 3

1. Clear the workbench by dragging all tools and glassware to the recycling chute.

2. Take a new gas piston from the Glassware tab of the Labware Shelf and place it on the Workbench.

3. Drag a balance from the Tools tab of the Labware Shelf and drop it directly on the gas piston. Record the mass of the empty piston.

4. Leave the gas piston on the balance and fill the piston with 50 mL of air from the air cylinder on the Chemicals Shelf. Record the mass of the piston with air.

5. Add 3 more increments of 50 mL of air, and record the total mass of the gas piston and air for each added increment.