Boyle’s Law

Boyle’s Law

Purpose: To verify Boyle’s Law.

Objectives
• To learn how to measure pressure using PASCO interface and sensors.
• To learn how to work with different volume and pressure units.
• To learn how to record, plot, and analyze data using a spreadsheet.
Equipment:
• A syringe
• Pressure sensor connected to Pasco Interface
Theory

The state of an ideal gas is characterized by three parameters: Pressure, Volume, and Temperature. When the temperature of the gas is kept constant, and the amount of the gas particles does not change, the product of the pressure and volume must also be constant. This is known as Boyle’s Law:

P × V  =   const.

Preliminary Setup.

• Set the syringe to 14 mL.
• Attach the syringe to the pressure sensor.
• Attach the pressure sensor to the Pasco Interface.

Note! After each measurement, bring the syringe to 14 mL again, before you take the next measurement. Do not leave the syringe at other volumes, or else the amount of air particles inside the syringe will change and the conditions will be inapplicable to Boyle’s law!

Some ballpark estimation! What approximately do you think is the pressure in the syringe right now?

 10 kPa 100 kPa 1000 kPa 10,000 kPa

Note! Keep in mind your answer, then. Your pressure measurements should be comparable to your correct estimate. If you get anything much smaller or larger, STOP! Either your sensor is not working properly, or you have installed it incorrectly. Correct the mistake before you continue!

Activity 1.

Measure the pressure in the syringe for various volumes

• Measure the pressure of the air for 14 mL and record it.
• Promptly, bring the syringe to 12 mL, measure the pressure, and release the syringe back to 14 mL. Record the pressure.
• Repeat for the volumes in the table below.
 Volume (mL) Pressure (kPa) P × V =

Data Analysis.

Questions

Question x. Can you convert mL into cc? What is 14 mL:

Question xx. Can you convert kPa into Pa? What is 101 kPa:

Question 1. Calculate the product of the pressure and volume, P × V, for each measurement and write it down in the table above.

Question 2. Is the product P×V the same for all measurements?

This is a tricky question! Your products are probably different, but that difference might be due to small errors and uncertainties in your measuring instruments, rather than be an actual difference. So, how do we determine what is an acceptable error?

Look at your values: at which digit does the disagreement appear? For example, 2.45 and 2.48 disagree in their third digit. 1.28 and 2.89 disagree in their first digit. Check the level of disagreement between your results:

Check for errors and re-do the experiment.

 First Digit シ Second Digit ッ List possible factors that could lead to errors: Third Digit ☺ Acceptable! Fourth Digit ☻ Really? Too good to be true! Check for errors!

Question 3. Can you plot your data?

Using Excel or other Spreadsheet (see Lab Resources on the right for reference) type in your data into the spreadsheet. Create a graph Pressure versus Volume.

How does the graph look?

Challenge Question. Calculate the inverse volumes, 1/V and plot your graph as Pressure versus (1/Volume).

 1/Volume (1/mL) Pressure (kPa)
How does the graph look?

Why would anyone want to plot graphs like that?