Revised 2/22/00 by Shane Phillips.

Boyle's Law

by: Dr. Laura Maki

This lab uses a spreadsheet program (Excel) to analyze gas pressure and volume data. Data will be given to the student to graphically demonstrate Boyle's law and to determine the number of moles of gas present.  The use of spreadsheets was covered in the first semester lab course, so this assignment should reinforce what you have already learned.  The instructions for using the spreadsheet may not coincide with your specific version, but they should certainly help point you in the right direction.

1. Experimental Data

Enter the data (given to you in lab): include a title for the table, and your unknown number. Be sure to format the table so the correct number of significant figures are present. You will be graded on the appearance of the information.

2. Plotting Pressure Vs Volume

 Create a chart of Pressure (Y-axis) Vs Volume (X-axis). Use a XY (Scatter) Plot
Use squares to designate each data point
*Include on your chart:
  1. Chart title
  2. Axis titles
  3. Your name and date in a text box
  4. Your Unknown number
The plot you get should look like a hyperbola. Print your chart.
Note: When asked to create a plot, always plot in the form Y Vs X (example: if asked to plot P Vs V, then you know that P is the y-axis and V is the x-axis).

3. Plotting Volume Vs 1/Pressure

Remember Boyle's law is:
This implies that pressure and volume are inversely proportional (i.e. if the pressure is increased the volume must be decreased).

We can rearrange equation (1) to give:
which is now in the form of an equation for a straight line of the type
where m represents the slope and b is the y-intercept of the straight line. From equation (2), if we plot V Vs 1/P for the data in worksheet 1, we will see a straight line with the slope equal to the value of k.

*Note that we are now plotting volume (V) on the Y axis unlike the chart we created in Step 2 above.

We must first make a column for data of 1/P (our X axis data):

Next to the pressure column on worksheet 1, add a column for 1/P. Use a formula to calculate 1/P (don't forget to use the = sign). Enter the data in the first cell and use the fill down option.
1/P is now our X axis data.
V is now our Y axis data.
(Remember in plotting on a spreadsheet, data must always
be in order of X, Y1, Y2, ... etc.  Alternatively, you can also use the
SERIES Tab in the "create a chart" window to specify the location
of your data with newer versions of Excel.)
Copy the volume data.
Paste it into the column to the right of 1/P. We now need to get the regression information including predicted Y values (new calculated Volumes): Use the analysis tools to determine the slope, y-intercept, and predicted y-values.
Copy the slope, y-intercept and predicted y values to your data.
Add the y-intercept  and (1/P) = 0 to the end of your data column.

On the same graph, plot:    1. Volume vs 1/P and         (Use squares for volume data.)
                                         2.  Predicted Y vs 1/P        (Use a solid line for predicted y values.)

 Be sure your line for the predicted Y values goes through zero, i.e. (1/P = 0).

*Include on your chart:

  1. Chart title
  2. Axis titles
  3. Your name and date in a text box
  4. Your Unknown number
  5. The value of k (from the slope) next to your best fit line (k = slope).
The plot should appear as a straight line. Print your chart.

4. Calculating the value of n. From Boyles' law data we can use the ideal gas law equation to solve for the number of moles of molecules present. Use 25°C (298K) as the temperature.

Ideal gas law equation:
PV = nRT
Rearranging to solve for V:
V = nRT/P
recalling that the slope of your line was 'k' and V = k * 1/P
Then
k = nRT
rearranging to solve for n:
n = k/RT

Calculate n on your data sheet.  Be sure to use an Excel function to do this.

5. Printing the Worksheet

Two different forms of the worksheet must be printed.

  1. The worksheet with a table (including predicted y vales), title for table, your name, the date, and the values for the slope and y-intercept, and the value for n (number of moles).
  2. The worksheet with formulas, rather than values.

        6. Submitting the Assignment

Before you turn in your project, check to be sure all of the items listed below are present:

  1. Chart of Pressure Vs Volume.
  2. Chart of Volume Vs 1/P (with best fit line) and value for k.
  3. Worksheet with data, slope, intercept, predicted y values, and n, (as numbers).
  4. Worksheet with data, slope, intercept predicted y values, and n, (as formulas).  Refer to tutorial (#12 Assignment) for instructions on doing this.

Forward to the Excel tutorial. Back to Chem 1112 main page.
Back to the CSUS Chemistry page.