# Datalogging in Science

## Boyle's Law

Mechanics

Boyle’s Law

Investigate how the volume occupied by a gas relates to the pressure acting on the gas.

Overview
In this experiment a fixed mass of dry air is drawn into a syringe. The syringe is connected to a pressure sensor. The piston of the syringe is depressed gradually and the pressure needed to compress the air into successively reduced volumes is noted. Graphs are then drawn to establish the nature of the relationship between the pressure of a gas and the volume that it occupies.
The recommended syringe has a volume of 20 ml.

Apparatus
A 20 ml syringe is connected by a short length of flexible tubing to a pressure sensor.

Procedure
1. Assemble the apparatus as shown (Fill the syringe with air before connecting it to the pressure sensor)

2. Connect the pressure sensor to the datalogger.

3. Connect the datalogger to the computer.

4. Open the
Graph programme
and set it to record Pressure in
Snapshot mode.

5. Prepare the software to receive manual input of volume measurements to match each Pressure reading recorded by the datalogger.

6. Push inwards gradually on the piston to increase the Pressure on the air in the syringe and thereby reduce its Volume. Record each new pair of values and enter them in a table as shown:

 Pressure Pa Volume cm^3 1 / Volume cm^ -3

Precaution:
Check the maximum pressure that the sensor is designed for and take care not to exceed
it.

Compress the air in the syringe very gradually to ensure that the temperature of the air does not increase.

Results
1. Plot a graph of Pressure against Volume and analyse it.

2. Plot a graph of Pressure against the reciprocal of Volume.

3. Express in words the relationship that your results suggest.

Questions
1. What would be the effect of compressing the air too quickly?

2. If after the last reading is taken, the pressure applied to the piston is reduced very gradually, will it return to its starting point?

3. What conclusion can be drawn from the outcome in Question 2 ?

4. Can a measure of the experimental error be determined from your work? If so, explain how and calculate the value.

Extensions
1. Start with the syringe half-full of air and record the change in pressure as the piston is withdrawn gradually. Plot a graph of fall in pressure as the volume increases. How does this compare with your original graph?

2. What would you expect to happen if the air in the syringe were replaced by a different gas (e.g. the gas available on tap in your laboratory)?

Data-Harvest users

1. Connect the sensor to the datalogger and the logger to the computer
2. Then click the Set Up icon to the right of this message.
3. When the software opens, click the Play button.

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