Higher Physics - Measuring the Density of Air at Sea-Level

Atmospheric Pressure (STP)

Harry Smith

September 27, 2011

1 Introduction

This document describes the procedure to measure the density of air at sea-level atmo-spheric pressure (1.2255kg/m3).

2 Apparatus

The apparatus required and justification for use is given in Table 1:

Scales Sensitive to 0.000001kgFlask Rigid - will not collapse under atmospheric pressureBung & tubing Suitable to seal flask and pump air in and outValve To seal the tubing - must be able to withstand pressureVacuum pump Suitable to remove all air from flaskLarge measuring cylinder Large enough to comfortably accommodate flask assemblyWater Enough to fill measuring cylinder 3

4 fullRubber gloves To ensure as little water is spilled as possible

Table 1: List of Apparatus Required and Justification for Use

1

3 Procedure

1. Assemble flask, bung and tubing.

2. Open valve and ensure flask is full of air.

3. Close valve.

4. Measure the mass of the full flask and tubing.

5. Connect vacuum pump to flask and remove all the air from flask.

6. Close valve.

7. Measure the mass of the empty flask and tubing.

8. Record volume of water in 34 -full cylinder.

9. Submerge empty flask and tubing in water fully, ensuring that the tubing nozzle isunder the surface and as little is spilled as possible (wear gloves!).

10. Open valve and allow flask to fill fully with water.

11. Close valve.

12. Remove flask (now full with water) from cylinder, ensuring that any water on thesurface of the assembly is shaken back into the cylinder.

13. Record the volume of water in the cylinder - the difference is now the volume of theflask.

4 Calculation

The density of air may be ascertained from the measurements taken in the procedure out-lined above.

Since we know density is defined as:

Density =Mass

Volume

We may use populate this equation as below:

Density of Air =(Mass of full flask from [1]) − (Mass of empty flask from [7])

Volume of water removed from cylinder from [13]

Q.E.D.

2