Densities Of Liquids Lab Report

Measurement of the Densities of Water and Alcohol
Phuc Truong and Shane Steele
Data Collected: September 8, 2014 2:05 P.M.
Purpose:
The purpose of the experiment is to measure the densities of liquids. Specifically, the two liquids that were used and measured in the research were deionized water (H2O) and alcohol (C2H5OH).
Methods:
Density is an intensive quantity that cannot be visually identified. Therefore, the most straightforward approach to this problem was to record the measurements of mass and volume. For volume of each liquid, the instruments used were a 50ml burette, a 50ml graduated cylinder and a 10ml gravity pipette. For each instrument above, the measurements were repeated 3 times. The mass of each sample was recorded by an electronic balance with the smallest gradation of 0.01g. The information collected then was used to determine the densities of water and alcohol.
Discussion:
The goal of using three different instruments for volume and
making 3 replicas of the measurements was to achieve a better precision and accuracy of the densities of water and alcohol. After having the mass and volume of each sample, the density of each liquid can be found by having mass divided by volume, with the unit of grams per milliliter.
From the data, 3 different densities of deionized water in association with 3 different instruments were acquired. For water, the measured densities were 0.86±0.12 g/ml, 0.993±0.006 g/ml and 0.989g/ml by using the 50ml burette, 50ml graduated cylinder and 10ml gravity pipette, respectively. However, the temperature at which the experiment was carried out was unknown. The reason this issue is raised is because the density of a liquid can change as the temperature changes.1 Therefore, it will be assumed that the experiment was conducted at room temperature, 25oC. The accepted literature value of the density of deionized water at room temperature is 0.99705 g/ml.2 The result collected from using the cylinder was the most accurate. The graduated cylinder has a smaller least count than that of the burette (0.1ml compared to 1ml), which resulted in higher accuracy. On the other hand, the gravity burette gave great precision but lower accuracy than the graduated cylinder did.
The question to find the density of alcohol was rather ambiguous.
Alcohol can be in an a mixture with water or a pure liquid. For this question, pure alcohol was assumed. Like measurements of water, with 3 different instruments, 3 different results were collected. The measured densities of alcohol were 0.67±0.04 g/ml, 0.803±0.004 g/ml and 0.790±0.004 g/ml. The accepted literature value of the density of pure alcohol is 0.78504 g/ml.3 From the results, it can be said that the density measured by the gravity pipette yielded the greatest accuracy.
From the experiment, it can be concluded that the instrument used in the process can affect greatly to the result. While the tools with smaller least counts give higher precision and accuracy, those with greater least counts do not. Furthermore, the result from the experiment is consistent with the fact that alcohol is lighter than water.
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1 Gilbert, Thomas R, Rein V Kirss, and Natalie Foster. 2013. Chemistry : an atoms-focused approach. New York: W. W. Norton & Company, Inc. pg 259
2 Tanaka, M. 2001. "Recommended table for the density of water between 0 C and 40 C based on recent experimental reports." Metrologia 301-309.
3 Haynes, W. M. 2010-2011. CRC Handbook of Chemistry and Physics. Boca Raton: CRC Press. pg 15-41