Ethanol is a colourless, volatile liquid with a pleasant smell. Its chemical formula is C₂H₅OH or CH₃CH₂OH.
It is completely soluble in water due to the presence of the polar –OH group, which can form hydrogen bonds with water molecules. Because of this, ethanol is widely used in solutions and mixtures.
Formula
- Ethanol contains two atoms of Carbon, one atom of Oxygen, and six atoms of Hydrogen.
- The chemical formula of Ethanol is C2H5OH, where -OH represents the alcohol functional group.
Structure of Ethanol
Ethanol has the molecular formula C₂H₅OH or CH₃CH₂OH.
It consists of:
- An ethyl group (C2H5–)
- A hydroxyl group (–OH)
- Two carbon atoms are single-bonded (C–C)
- First carbon is attached to three hydrogen atoms (CH3)
- Second carbon is attached to: Two hydrogen atoms, one –OH group
Physical Properties of Ethanol
The physical properties of ethanol are mainly determined by the presence of the polar hydroxyl (–OH) group. This group enables intermolecular hydrogen bonding, which influences properties such as solubility, boiling point, and volatility.
- Colour, Odour and State: Ethanol is a colourless liquid. It has a pleasant, characteristic smell. It is transparent and mobile (flows easily).
- Solubility in Water: Ethanol is completely miscible with water (mixes in all proportions). Due to hydrogen bonding between the –OH group of ethanol and Water molecules.
- Boiling Point: The boiling point of ethanol is 78°C. It is higher than that of hydrocarbons with similar molecular mass due to the presence of intermolecular hydrogen bonding between ethanol molecules, which requires more energy to break.
- Volatility: Ethanol is volatile, it evaporates easily at room temperature, which is why it gives a cooling effect on the skin.
- Density: The density of ethanol is 0.79 g/cm³. Less dense than water,however, it does not float on water because it is completely miscible with it.
- Hydrogen Bonding: Ethanol molecules form hydrogen bonds with each other and with water. This affects Boiling point, Solubility and Physical state.
- Electrical Conductivity: Ethanol is a non-electrolyte. Does not produce ions in solution.
Chemical Properties of Ethanol
Ethanol shows a variety of chemical reactions such as combustion, oxidation, and substitution due to the presence of the –OH group.
1) Combustion: Ethanol burns in air to form carbon dioxide and water. Burns with a blue flame and used as a clean fuel.
C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O + \text{heat}
2) Reaction with Sodium: Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas
2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2
3) Oxidation: Ethanol is oxidised to ethanoic acid using oxidising agents alkaline KMnO₄ and acidified K₂Cr₂O₇. KMnO₄ changes from purple to brown and K₂Cr₂O₇ changes from orange to green.
3CH_3CH_2OH + 2KMnO_4 \rightarrow 3CH_3COOK + 2MnO_2 + 2KOH + 2H_2O
4) Dehydration: On heating with concentrated H₂SO₄ (443 K), ethanol forms ethene. This is an elimination reaction.
C_2H_5OH \xrightarrow{\text{conc. } H_2SO_4,\ 443K} C_2H_4 + H_2O
5) Esterification: Ethanol reacts with ethanoic acid to form an ester (pleasant smell).
C_2H_5OH + CH_3COOH \xrightarrow{\text{conc. } H_2SO_4} CH_3COOC_2H_5 + H_2O
Preparation of Ethanol
Ethanol is prepared mainly by two methods:
1) Fermentation of Sugars
- Sugars like glucose are converted into ethanol using yeast (zymase enzyme).
- This process occurs in the absence of air (anaerobic conditions).
C_6H_{12}O_6 \xrightarrow{\text{yeast}} 2C_2H_5OH + 2CO_2
- Done at temperature around 300–310 K
- Produces carbon dioxide gas
- Used in making alcoholic beverages
2) Hydration of Ethene
- Ethene reacts with steam in presence of acid catalyst (phosphoric acid).
\mathrm{C_2H_4 + H_2O \rightarrow C_2H_5OH \ (H_3PO_4)}
- Temperature should be 573 K
- Pressure should be 60–70 atm
Uses of Ethanol
Ethanol is a versatile organic compound widely used in various fields due to its solvent properties, flammability, and antiseptic nature.
- Ethanol is used as a fuel and as an additive in petrol (bioethanol) because it burns cleanly.
- It is widely used as a solvent in medicines, perfumes, paints, and varnishes.
- Ethanol is used as an antiseptic in sanitisers and medical products to kill germs.
- It is the main component of alcoholic beverages such as wine and beer.
- Ethanol is used in the chemical industry for the preparation of substances like ethanoic acid and esters.
- It is used as a preservative for biological specimens.