The Alcohol Content of Whiskey

Introduction

The purpose of this experiment was to determine the alcohol content of a sample of whiskey and a sample of vodka. To achieve the purpose of the experiment, the entire class worked to obtain the densities of a wide range of ethanol/water mixtures. These densities were put into a plot that related them to their percent composition, and were compared to the densities of the whiskey and vodka samples.

Procedure

Different alcohol/water solutions were assigned to each student. Volumetric pipets were used to prepare three 10.0 mL samples that composed of 4.5 mL ethanol and 5.5 mL water, creating the assigned 45% ethanol solution. The samples were combined in a beaker and covered and then 5 mL were withdrawn using the volumetric pipet and put into pre-weighed vials. The vials were weighed again and their masses recorded. For each of the 5 mL solution samples, the mass without the vial and the density were calculated, along with the average density and the standard deviation using a TI-83 Plus calculator. The data of each of the different assigned ethanol/water solutions, the whiskey, and the vodka, were combined and put onto an Excel document, and made available to the class. The average densities and standard deviation of the whiskey and vodka samples were calculated on Excel. A scatter plot was produced of the density vs the percent composition on the ethanol/water solutions. It was determined that the data was linear so an equation was calculated and plotted using Excel that best fitted the to the data. The calculated densities of the whiskey and vodka where plugged into the equation to calculate the alcohol content of the whiskey and vodka.

Detailed procedures may be found in reference 1.

Results

Figure 1 shows a plot of the densities calculated of the samples of different ethanol/water compositions. Figure 1 is important because it allowed me to easily see if there was a pattern in the data, to see how close that data was, and use the equation of the best-fit to calculate alcohol content of the whiskey and vodka samples.

Figure 1. Scatter plot of the calculated densities of the ethanol/water samples.

From the calculated average densities of the whiskey and vodka and the equation of best-fit line in Figure 1, the alcohol concentration of the whiskey was calculated to be 36.2% (v/v) and the vodka’s  to be 35.7% (v/v). The calculated PRE of the whiskey is 9.63% and the calculated PRE of the vodka is 10.9%.

Discussion

The the plot (figure 1) had a respectable R2 value of 0.9632 and there were no outliers, but the majority of the points were not directly on the best-fit line. The points were linear pattern, the average density decreased as the ethanol concentration increased. The concentration of alcohol in the sample of whiskey (36.2% (v/v)) and the sample of vodka (35.7% (v/v)) as calculated from the best-fit line in figure 1, were less than the reported concentration of alcohol (40% (v/v)) given on the label of the bottles. The PRE of the whiskey was 9.63% and the PRE of the vodka was 10.9%. The differences in the calculated concentrations and the reported may have been caused by not making precise measurements, and the assumption that the whiskey and vodka only contained ethanol and water. Because the calculated and the reported concentrations of the whiskey and vodka were different, the fundamental assumption that they only contain alcohol and water is not valid. The data points in figure 1 appeared to be fairly precise, which made the rejection of that assumption more valid.

References

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