Theo Nash
A mixture of alcohol and water is called an aqueous alcohol. When water is mixed with alcohol, hydrogen bonds can form between the alcohol molecules, between the water molecules, and between water and the alcohol molecules. The most common mixture of alcohol and water is ethanol and water. This mixture can be separated using distillation because both have different boiling points and are miscible liquids.
| Characteristics | Values |
|---|---|
| Name of mixture | Ethanol |
| Boiling point | 351.3 K (78.1 °C) |
| Miscibility with water | Yes |
| Miscibility with alkanes | Yes, up to undecane |
| Volume | Less than the sum of its parts |
| Reaction | Exothermic |
| Energy released | Up to 777 J/mol at 298 K |
| Flash point | 25 °C (77 °F) for 20% alcohol by mass |
| Historical names | Aqua vitae, "water of life" |
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What You'll Learn
The mixture's unique properties
A mixture of ethanol and water is called an ethanol-water solution or aqueous alcohol. This mixture has some unique properties due to the chemical interaction between the two substances.
Firstly, the mixture of ethanol and water forms an azeotrope, which means that the two substances have a constant boiling point and cannot be separated by simple distillation. The boiling point of the ethanol-water azeotrope is 78.1 °C, which is lower than that of pure water (100 °C) but higher than that of pure ethanol (78.37 °C). This property can be used to separate the two components through distillation, as the ethanol will evaporate and condense first, leaving the water behind.
Secondly, the ethanol-water mixture exhibits negative excess entropy and negative excess volume. This means that when ethanol and water are mixed, the resulting volume is less than the sum of the individual components' volumes due to the attraction between the two substances. Additionally, the mixing of ethanol and water is exothermic, releasing heat energy of up to 777 J/mol.
Thirdly, the hydrogen bonding between water and ethanol molecules in the mixture is unique. Water can form four hydrogen bonds, while ethanol can only form three. When mixed, the water molecules form stiff clathrate cages around the ethanol molecules, enhancing the hydrogen bonding of the ethanol hydroxyl groups. However, when the volume ratio of ethanol exceeds 20%, a phase transition occurs, and the water molecules start forming hydrogen-bonded links between the ethanol molecules instead.
Finally, the ethanol-water mixture has interesting medicinal and historical aspects. John of Rupescissa, a 14th-century scholar, regarded ethanol as a "life-preserving substance" or "aqua vitae," believing it could prevent all diseases. The distillation of alcohol also has a long history, with archaeological evidence of true distillation dating back to the 12th century in China and the 14th century in India.
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How to separate the two liquids
A mixture of alcohol and water is called an ethanol-water solution or ethanol-water mixture. Here are several methods to separate the two liquids:
Freeze Distillation
This method relies on the different freezing temperatures of alcohol and water. You will need a container that can withstand freezing and thawing, and a freezer or outdoor temperatures below 0 °C (32 °F). Start with a liquid that is 5%-15% alcohol, and place it into the container. As water expands when it freezes, ensure that your container is large enough to hold the expanded liquid without bursting. The water content of the liquid will freeze and expand, but the alcoholic content will remain liquid. Remove the frozen material, which will mainly be water, leaving behind a liquid with a higher alcohol content. This method does not produce pure alcohol and does not remove impurities.
Distillation with Salt
This method uses ordinary table salt to separate isopropyl alcohol from water. You will need a wide-mouth glass jar for mixing, non-iodized table salt, a container to hold the finished liquid, and a baster with a reduced-size nozzle. Start by filling the mixing container about one-quarter full of table salt, ensuring it is not iodized. Then, add the original isopropyl alcohol mix (50% to 70% isopropyl alcohol) and use the baster to draw out the separated liquid. This process will result in condensed isopropyl alcohol, not drinking alcohol.
Distillation by Heating
This method involves creating a closed system for distillation. You will need a round-bottomed glass flask (or boiling flask), a condensing unit, and a second glass container for the separated liquid. A fractional column inserted between the boiling flask and the condensing unit can improve the separation. Heat the alcoholic water mixture in the round-bottomed flask to 80 °C (176 °F). The simple distillation system requires a large difference in the boiling points of the two liquids, and while it uses less heat and is easier to set up, it provides less accuracy in separating alcohol from water.
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The history of alcohol distillation
The process of distillation comes from the Latin 'de-stillare', which means 'drip or trickle down'. It involves separating a liquid through evaporation and condensation.
In the first century, the Greek physician Pedanius Dioscorides described the process of distillation after observing the condensation on a vessel's lid while heating mercury. The invention of the alembic, a key distillation apparatus, is attributed to Maria the Jewess, Zósimo of Panoplies, or his sister Theosebeia around AD 200-300. The Arabs further refined the alembic in the 8th or 9th century to obtain finer essences for perfumes and attempted to use it to convert base metals into gold.
The first documented use of distilled alcohol comes from a 12th-century Italian medical school, where it was used for medicinal purposes and referred to as "spirited water" or "aqua vitae", meaning "water of life". The medicinal properties of ethanol were also studied by Arnald of Villanova (1240-1311 CE) and John of Rupescissa (c. 1310-1366), who regarded it as a life-preserving substance.
In the 11th century, a major change in distillation occurred with the invention of a coiled cooling pipe by Avicenna, a medieval alchemist. This innovation allowed for more effective cooling of plant vapour and steam compared to previous methods that used straight cooling pipes. The knowledge of distillation spread throughout Europe during the Turkish invasions of the 14th and 15th centuries, and the production of distilled spirits became more widespread.
By the early 19th century, large-scale continuous stills were operating in France and England, thanks to innovations by Robert Stein and Aeneas Coffey. These stills allowed for constant distillation and contributed to the industrialization and large-scale commercial distilling of alcoholic beverages.
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The chemical reaction
When water and alcohol are mixed, a chemical reaction occurs, and the resulting liquid consists of water and alcoholic and mixed water/alcoholic clusters. This mixture is known as an azeotrope. The process of mixing the two substances is exothermic, with up to 777 J/mol of energy released at 298 K.
The type of alcohol involved in the mixture also affects the chemical reaction. For example, methanol, ethanol, and propanol are miscible with water in all proportions, forming non-ideal solutions. Ethanol, a primary alcohol, has the ability to form hydrogen bonds with water due to its hydroxyl group. The presence of acid catalysts can cause ethanol to react with carboxylic acids, producing ethyl esters and water. This reaction is commonly performed on a large scale in industrial settings and requires the removal of water from the mixture as it forms.
The distillation process is commonly used to separate water and alcohol mixtures, as they have different boiling points. Alcohol has a boiling point of approximately 78.37°C, while water boils at 100°C. During distillation, alcohol evaporates first and can be collected from the condenser outlet, leaving water behind in the distillation flask. This technique is employed in various applications, including the production of distilled beverages with high alcohol content and desalination.
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The dangers of mixing
While some people mix water and wine to pace themselves and avoid a hangover, it is generally advised against. Mixing water with wine will not prevent a hangover, and it changes the wine's chemical composition, potentially ruining its flavour and aroma. This is because water and alcohol do not fully mix, even at their purest levels, resulting in an odd concoction of liquids that do not blend well.
Similarly, adding water to whiskey can dilute the ethanol, which may slightly numb your taste buds and make them less sensitive to certain flavours. However, it can also enhance certain flavours by promoting their release back into the solution. For example, adding water to whiskey can cause ethanol molecules to cluster and trap volatile flavour compounds. Cooling the solution or diluting it can then release these compounds, potentially improving the aroma and flavour.
Mixing ethanol and water releases up to 777 J/mol at 298 K, and the mixture has a lower volume than the sum of its individual components. An ethanol-water solution will catch fire if heated above its flash point and an ignition source is applied. For a solution of 20% alcohol by mass (about 25% by volume), this will occur at around 25°C.
In conclusion, while it may be tempting to mix water with alcoholic beverages to avoid dehydration or to enhance flavour, it is important to be aware of the potential dangers. Mixing water with alcohol can alter the chemical composition of the beverage, affecting its taste and potentially causing an unpleasant drinking experience. Additionally, ethanol-water mixtures can be flammable under certain conditions, posing a safety risk if not handled properly.
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Frequently asked questions
A mixture of alcohol and water is called an azeotrope.
An azeotrope is a mixture of two liquids with different boiling points that are nonetheless difficult to separate via distillation.
Due to their different boiling points, distillation is the best way to separate a mixture of alcohol and water. Alcohols have a boiling point of 78.37°C while water has a boiling point of 100°C.
When water is mixed with alcohol, hydrogen bonds form between the alcohol molecules, between the water molecules, and between water and the alcohol molecules.
