Ethanol or ethyl alcohol has historically been produced through the yeast fermentation of carbohydrates-starches and sugars-dissolved or suspended in water. Although often it is the pure alcohol end product that is desired, there are times when it is combinations of these two in differing proportions and their behavior that is important. One particularly important variable in studying ethanol water mixtures is the measure of their combined densities.
Overly Simplistic Methodology
Densities of ethanol water mixtures, because of their importance, are definitively known to great accuracy. An in-gathering of data has been necessary because the composite density of the two components ethanol and water cannot be determined simply by multiplying the fraction of ethanol times its density and adding the fraction of water times its density. By way of illustration-if a mixture was made of 75 percent ethanol to 25 percent water-the density of pure ethanol being 0.78934 and that of pure water being 1.00000 (Handymath Density and Concentration Calculator). The simple mathematical relation is written,
- Total Density = 0.75 (0.789) + 0.25 (1.000) = 0.842
In fact, the true density of that mixture of ethanol at 20 degrees C is closer to 0.856. The reason for the deviation from linear behavior-that is the behavior such a simple mathematical equation as the above calls for-is because ethanol and water do not simply mix independently of each other. They interact chemically, with the liberation of heat, due to the phenomenon called “hydrogen bonding”. Both water and alcohol possess hydroxyl groups. These form a partial bond between the hydrogen atom of one molecule and the oxygen atom of another molecule (University of Illinois at Urbana-Champaigne).
Obtaining Quality Data
Because of this, the easiest route to accurate data is to obtain it empirically-by measurement. Once the data has been gathered, it may then be modeled, or transformed into sophisticated mathematical expressions, using CAD-computer aided design software-that include three essential variables-the ratio of water to ethanol, the temperature of the mixture, and its composite density (IOP Science). All of this is part of the field known as metrology-the scientific study of measurement. Data to five digits is readily available, some of it even via the Internet.
One important application of ethanol and water mixture density data is the calibration of ultrasound imaging equipment for the medical profession. Sound is propagated through ethanol water mixtures; the density determines the speed of transmission. The apparatus can be calibrated or adjusted to maximize equipment performance resulting in superior images.
For Drugs and Food
Another vital medical use for ethanol water mixture density data includes the predicting of the solubility of drug components for pharmaceuticals. This can be a real problem, as drug components often consist of large molecules. Size of molecules tends to reduce solubility. Of recent interest in this regard is the so-called Jouyban-Acree model, derived by scientists A. Joyban, S. Soutanpour and W. Acree, Jr.
One application of ethanol water mixture density determination of perhaps greatest interest to the masses is its use in determining end point in the manufacture of alcoholic beverages, including beer, wine, and spirits.