The overall structure of a formal report is described in the section Writing a Formal Report of this manual.  This example was edited based on one written previously by Hilary Chaney, a former student of this course:^[1]

Density of Water Measured Using Different Devices

Introduction

In chemistry, many reactions occur with reactants and/or products in aqueous solutions or in other solvents. At other times, reactions take place involving reactants in the liquid phase are found. When studying these samples, often it is important that measurements of volume are completed as accurately as possible.

To determine the accuracy – defined as the extent to which the measured quantity matches the true quantity – we need to be able to compare measurements made using this equipment with those made using a standard. Since standard, reproducible volumes of liquids are difficult to obtain, we instead determine the density of a known liquid using both the glassware and a common balance, and compare the densities measured with the published density for this liquid.

The density of a liquid is defined as

(1)  

which can be measured for a given sample by measuring both its mass and volume. In this experiment, we measure the mass of a measured volume of deionized water delivered into a beaker using various pieces of glassware with a balance. The resulting density measurements were compared with density values reported by Wentworth and Munk (1).

Methods

Known volumes of deionized water was measured using (in turn) a beaker, a graduated cylinder and a buret. A digital balance was used to determine the mass of each sample of water. As the number of significant figures reported on the digital balance significantly exceeds the number of significant figures reported on the A digital thermometer was used to determine the temperature of the deionized water with which the known density can be obtained from ref. 1.

Results

The density of water measured using the three devices are listed in Table 1 below, along with the percent error for the density of water compared to the published value. The beaker is the least accurate measuring device, while the buret is the most accurate measuring device. This can be deduced based on the decreasing percent error for more accurate glassware.

Discussion

The results show that while a reasonable level of accuracy expected for most experimental purposes can be obtained using a volumetric buret for quantitative applications, and for most qualitative and semi-quantitative purposes (such as preparing reaction mixtures) by using a graduated cylinder. However, the beaker provides only a rough estimate for the volume of water that is delivered. That said, since the time required to set up and perform the measurements increase as the accuracy increases, the less accurate pieces of glassware are still somewhat useful.

While this work provides evidence for the relative accuracy of different types of glassware, a number of questions remain. Firstly, while this conclusion is true for water, it is unclear whether this is also true for other liquids, given that the surface properties differ for different liquids2. Therefore, the results of this study are probably limited to dilute aqueous solutions. Another significant limitation of this work is that only one trial was conducted for each piece of glassware. Therefore, it is not possible for the precision of this glassware to be evaluated based on the results of this experiment alone.

Conclusion

Of the pieces of glassware evaluated in this experiment, the 100 mL beaker is the least accurate for determining the volume of water, while the buret is the most accurate. This experiment can be extended further by repeating the experiment using the same glassware to evaluate the precision of the glassware, as well as to evaluate the efficacy of this glassware to measure liquids other than water by determining the density of other reagents using the same methods.

Bibliography

1. Wentworth, R. A. D. and Munk, B. H. Experiments in General Chemistry: Laboratory Manual, 10th Ed.; Brooks/Cole: Belmont, CA, 2013.
2. Brown, T. L., LeMay, H. E., Bursten, B. E., Murphy, C. J. and Woodward, P. M. Chemistry – The Central Science, 12th Ed,; Prentice Hall: Boston, MA, 2012.