Determination of Water Density

Introduction

The purpose of this experiment was to compare the precision of some of the laboratory instruments and determine the density of purified water. The density of water was determined using three different volume-measuring devises. Five milliliters of water was measured using the three different volume-measuring devises three times each, and was then weighed on the analytical balance.

Procedure

Three vials were cleaned and then weighed on the analytical balance. Using a 100 mL graduated cylinder, five milliliters of water were measured and poured into each of the vials. The vials were then weighed on the analytical balance again and their masses recorded. The vials were dried, and the steps repeated using a 100 mL graduated pipet and again using a volumetric pipet. The density of water was calculated for masses of the three different measuring devises. The densities were then compared to each other and to the actual density of water.

Results

Tables one, two, and three show the mass of the vials and the mass of the vials containing water that was measured using the three different volume-measuring devises.

Table 1: Data obtained using a 100 mL graduated cylinder to measure a 5.0 mL sample of water. 

Trial	Mass of vial (g)	Mass of vial and water (g)
1	19.8155	24.745
2	20.6247	23.7373
3	21.2078	24.848

Table 2: Data obtained using a 100 mL graduated pipet to measure a 5.0 mL sample of water.

Trial	Mass of vial (g)	Mass of vial and water (g)
1	19.8155	24.9443
2	20.6247	25.4928
3	21.2078	26.1954

Table 3: Data obtained using a 100 mL volumetric cylinder to measure a 5.0 mL sample of water.

Trial	Mass of vial (g)	Mass of vial and water (g)
1	19.8155	24.7281
2	20.6247	25.2298
3	21.2078	25.6645

After the masses were determined, the densities of the data were calculated with the Microsoft Excel program. The Excel worksheet is stapled to this report.

Table 4: Average density water obtained from each devise. 

Measuring devise	Average density (g/mg)
100 mL Graduated Cylinder	0.9859 + or - 0.1869
100 mL Graduated Pipet	0.99897 + or - 0.02610
5.00 mL Volumetric Pipet	0.98252 + or - 0.04651

Discussion

The lab was fairly successful in accurately determining the density of water and the precision of the instruments. The second set of data, where the graduated pipet was used to measure the water volume, is the most accurate with a percent relative error of 0.097 when compared with the given density of water. The data where the graduated cylinder was used is slightly less accurate with a percent relative error of 1.21. This is most likely because it is more difficult to have precise measurements using a graduated cylinder. The data collected from the volumetric pipet is the least accurate with a percent relative error of 1.55. This is most likely because the instrument takes more practice and skill to use correctly than the other instruments, or it is not as precise as the other measuring instruments. 

References

1. General Chemistry Experiments: A Manual for Chemistry 204, 205, and 206, Department of Chemistry, Southern Oregon University: Ashland, OR, 2009