Ever wondered what connects your favourite K-pop stars’ favourite traditional Korean drinks like Makgeolli to Chemistry? The answer lies in the fascinating world of alcohols!
You may associate alcohols with only alcoholic beverages such as makgeolli and soju, however, in Chemistry, alcohols are a whole group of compounds with unique properties and important roles. So, let’s take a closer look at the science behind how it works!
What are Alcohols?
In chemistry, alcohols are organic compounds that contain a hydroxyl (-OH) group attached to carbon atoms. This functional group is what gives them their distinctive properties.
The general formula is as follows:
Alcohols can also exist in different forms, known as isomers, which are compounds that have the same molecular formula but different structures, existing as either straight chain or branched structures. Isomers also share similar chemical properties but have different physical properties.
Alcohols & Its Structure
Physical Properties of Alcohols
Alcohols are fascinating because of their wide range of physical properties.
Melting and Boiling Points
Alcohols typically have higher boiling points than other organic compounds of similar size due to hydrogen bonding. As the number of carbon atoms in an alcohol increases, its melting and boiling points also rise. For example, ethanol, the primary alcohol in drinks like makgeolli and beer, has a boiling point of 78.37°C. In contrast, butanol, which has more carbon atoms, has an even higher boiling point of 117.7°C. This is because larger alcohol molecules experience stronger intermolecular forces, requiring more heat energy to overcome these forces.
Volatility
Alcohols are volatile, meaning that they evaporate easily. This is why you can often smell it in beverages like beer, even without taking a sip!
As the number of carbon atoms in an alcohol increases, their volatility decreases. This is because a higher relative molecular mass leads to stronger intermolecular forces between the alcohol molecules, requiring more energy to vaporise them. As a result, ethanol is more volatile than longer-chain alcohols like butanol, which are less likely to evaporate at room temperature.
Density
Alcohols are typically less dense than water, which is why they often float when mixed with water-based liquids. However, as the number of carbon atoms in an alcohol increases, its density also increases. For example, in this video, you can observe how alcohol behaves differently in terms of density when compared to water.
Viscosity
Viscosity, or the thickness of a liquid, varies among alcohols. As the length of the hydrocarbon chain in alcohols increases, the liquids become more viscous, meaning they flow less easily. This increased viscosity is due to the stronger intermolecular forces that arise from the additional carbon atoms, causing the molecules to stick together more tightly.
For example, ethanol, with its shorter two-carbon chain, is relatively thin and flows easily. In contrast, butanol, which has a longer four-carbon chain, is noticeably thicker and flows more slowly due to its increased viscosity. This difference depicts how the length of the hydrocarbon chain in alcohols directly affects their viscosity.
Flammability
As the number of carbon atoms in alcohols increases, their flammability decreases. Larger alcohol molecules are more challenging to ignite. For instance, methanol burns more easily compared to ethanol and isopropanol, which have longer carbon chains.
Check out this video to see how methanol, ethanol, and isopropanol compare in terms of how well, fast, and brightly they burn.
Solubility in Water
Alcohols are generally soluble in water, but their solubility decreases as the number of carbon atoms increases.
How Alcohols Are Made
The production of alcohols is where the chemistry really shines.
One of the most traditional methods is fermentation.
Fermentation
Fermentation is a process whereby glucose or sugar is broken down by microorganisms, like yeast, into smaller molecules like ethanol and carbon dioxide.
For example, in making makgeolli, yeast enzymes would act as catalysts, converting glucose into ethanol and carbon dioxide, to give us that slightly sweet but fizzy drink that’s a staple in Korean culture.
Take a look at this video to see how the fermentation process to make makgeolli works!
Manufacture of Ethanol from Ethene (Hydration)
But alcohols aren’t just made in traditional settings. In industrial processes, ethanol can be manufactured from ethene through hydration. This involves reacting ethene with steam at a high temperature of 300°C and 60 atm pressure, with phosphoric(V) acid as a catalyst.
This method is a more controlled and large-scale way to produce alcohols, ensuring that the ethanol produced is pure and suitable for various uses beyond beverages.
Chemical Reactions of Alcohols
Alcohols aren’t just passive players in chemistry; they participate in several important reactions. These reactions not only demonstrate the versatility of alcohols but also their importance in the synthesis of various compounds.
Combustion
Alcohols burn in oxygen to produce carbon dioxide and water.
However, if there’s an insufficient supply of oxygen during combustion, the process becomes incomplete, leading to the production of carbon monoxide and water instead of carbon dioxide. This incomplete combustion is less efficient and can be dangerous due to the toxic nature of carbon monoxide.
Oxidation
Alcohols like ethanol can be oxidised to produce carboxylic acids like acetic acid. For instance, using an oxidising agent and heat, ethanol can be converted to acetic acid.
If potassium permanganate is used, you’ll observe the purple solution turning colourless. On the other hand, using potassium dichromate would turn the orange solution green.
Esterification
Esterification, where alcohols react with carboxylic acid to form an ester and water, is widely used in the production of flavourings and fragrances. In this reaction, ethanol reacts with acetic acid in the presence of concentrated sulfuric acid and heat under reflux to form ethyl acetate and water.
A Summary: Chemical Reactions of Ethanol
The Many Uses of Ethanol
Ethanol is incredibly versatile. It’s not only used in alcoholic drinks but also as a solvent for many organic compounds due to its ability to dissolve organic compounds. Its high volatility makes it ideal for use in perfumes and deodorants. Ethanol is also a clean-burning fuel, producing only carbon dioxide and water when combusted, making it an environmentally friendly option for powering vehicles and generating energy.
The Chemistry Behind the Making of Alcohols
From the makgeolli that’s enjoyed with Korean BBQ to the ethanol used in your hand sanitizer, alcohols are everywhere. And now, with a better understanding of their properties, production, and reactions, do you better understand how alcohols are such an essential part of both chemistry and culture?
