Background:
Boyle’s law describes that for a fixed quantity of gas the pressure and volume are inversely proportional. In this dry lab students will analyze pre-determined pressure and volume data pairs that will be used to show their mathematical relationship. Students are to use the data that is provided to solve the lab questions and post-lab analysis based on their knowledge and understanding of Boyle’s Law.
Pre-lab Questions:
Complete ALL of these questions prior to beginning the experiment
- Define Boyle’s Law:
- Define the term inverse proportionality:
- Define the term direct proportionality:
- Describe how direct and Inverse proportionality differ from each other.
- A sample of nitrogen at 20oC was compressed from 300 mL to 0.360 mL and its new pressure was found to be 400.0 Pa. What was the original pressure in kPa?
- The pressure on 6.0 L of a gas is 200 kPa. What will the volume be, if the pressure is doubled, while keeping the temperature constant (the same)?
Objectives/Aims:
- Determine the relationship between pressure and volume of the gas.
- Describe the relationship between gas pressure and volume in a mathematical equation.
- Use the results to predict the pressure at other volumes.
Table 1: Pressure vs Volume Data table
| Volume (mL) | Pressure (kPa) | Constant, k | 1/ Volume (Post Lab Analysis) | |
| (P * V) | ||||
| 5.8 | 175.9 | |||
| 7.8 | 131.4 | |||
| 9.8 | 105.1 | |||
| 11.8 | 87.0 | |||
| 13.8 | 74.4 | |||
| 15.8 | 65.1 | |||
| 17.8 | 57.6 | |||
| 19.8 | 52.0 | |||
Data and Results:
Plot the Pressure and volume data in excel as detailed below. Using Excel, indicate the slope of the line. Include the graph in your report submission. (Plot Pressure on Y-axis, Plot Volume on X-axis).
Post-Lab Questions:
- If the volume is doubled from 5.0 mL to 10.0 mL, what does your data show happens to the pressure? Show the pressure values in your answer.
- If the volume is halved from 20.0 mL to 10.0 mL, what does your data show happens to the pressure? Show the pressure values in your answer.
- From your answers to the first two questions and the shape of the curve in the plot of pressure vs. volume, do you think the relationship between the pressure and volume of a confined gas is direct or inverse? Explain your answer
- What experimental factors are assumed to be constant in this experiment?
- One way to determine if a relationship is inverse or direct is to find a proportionality constant, k, from the data. If this relationship is direct, k = P/V; if it is inverse, k = P × V. Based on your answer to Question 4, calculate k for the seven ordered pairs in your data table (divide and multiply the P and V values). Show the answers in the third column of the Data and Calculations table.
- How constant were the values for k that you obtained in Question 6? Good data may show some minor variation but the values for k should be relatively constant.
- Using P, V, and k, write an equation representing Boyle’s law.
- Write a verbal statement that correctly expresses Boyle’s law.
Post-Lab Analysis
To confirm that an inverse relationship exists between pressure and volume, a graph of pressure vs. reciprocal of volume (1/volume) may also be plotted. To do this you will need to create a third column in your data table that contains the values equal to 1/volume.
Calculate regression statistics and plot a best fit regression line on your graph of pressure vs. 1/volume. The linear-regression statistics for these two data columns are displayed in the form
y = mx + b
where x = 1/volume
y = pressure
m = a proportionality constant (k)
b = y-intercept
If the relationship between pressure and volume is an inverse relationship, the graph of pressure vs. 1/volume should be direct; that is, the curve should be linear and pass through (or near) the origin. Examine your graph to see if this is true for your data.
