- Combustion: Alcohols burn in air to give CO₂, H₂O, and heat. Ethanol burns with a pale blue flame.
- Oxidation: Alcohols oxidise to aldehydes and then to acids using acidified K₂Cr₂O₇ or KMnO₄.
- Reaction with Sodium: Forms alkoxides and H₂ gas with effervescence (e.g., sodium ethoxide).
- Esterification: React with acetic acid in the presence of conc. H₂SO₄ to form fruity-smelling esters.
- Dehydration:
- At 170°C → forms alkene (e.g., ethene)
- At 140°C → forms ether (e.g., diethyl ether)
Definitions [1]
Definition: Alcohol
Alcohols are the hydroxyl (-OH) derivatives of alkanes. They are formed by replacing one or more hydrogen atoms of the alkane with an OH group.
Chemica Equations [1]
Chemical Equation: Hydration of Ethene
Method 1:
\[\mathrm{C}_{2}\mathrm{H}_{4}+\mathrm{H}_{2}\mathrm{SO}_{4}\quad\xrightarrow[30\mathrm{~atm}]{80^{\circ}\mathrm{C}}\quad\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{HSO}_{4}\]
Ethene
\[\begin{array}
{rcl}\mathrm{C_2H_5HSO_4} & + & \mathrm{H_2O} & \to & \mathrm{C_2H_5OH} & + & \mathrm{H_2SO_4} \\
\text{Ethyl hydrogen} & & \mathrm{(Boiling)} & & \mathrm{Ethanol} \\
\mathrm{sulphate}
\end{array}\]
Method 2:
\[\mathrm{C_2H_4~+~H_2O~\frac{H_3PO_4}{300^\circ C,~60~atm.}C_2H_5OH}\]
Key Points
Key Points: Alcohols
- Alcohols are hydroxyl (-OH) derivatives of alkanes, formed by replacing one or more hydrogen atoms with an -OH group.
- Alcohols are classified as:
- Monohydric (e.g., Methanol, Ethanol)
- Dihydric (e.g., Ethylene glycol)
- Trihydric (e.g., Glycerol) - Ethanol (C₂H₅OH) is produced by fermentation of sugar or by cracking petroleum (ethane source).
- Ethanol is used in wines (spirit of wine) and is also known as grain alcohol.
- Isomerism in alcohols occurs in compounds with three or more carbon atoms (e.g., propanol and butanol have isomers, but neither methanol nor ethanol does).
Key Points: Physical Properties of Alcohols
| Property | Details |
|---|---|
| Nature | Inflammable, volatile, colourless liquids with a faint odour and burning taste |
| Boiling Point | Increases with molecular weight • CH₃OH: 64.5°C • C₂H₅OH: 78.3°C |
| Solubility | Soluble in water and organic solvents |
| Density | Ethanol is lighter than water; specific gravity = 0.79 at 293 K |
| Toxicity | Methyl alcohol is toxic and can cause blindness or death if consumed |
key Points: Chemical Properties of Alcohols
Key Points: Uses of Ethyl Alcohol
- Uses: Ethanol is used as a solvent, preservative, chemical raw material, in alcoholic beverages, and as a fuel or antifreeze.
- As a beverage: Ethanol is present in drinks — beer (~4%), wine (~11%), and spirits (~40% or more).
- Denatured alcohol (Methylated spirit): Ethanol mixed with methyl alcohol, dye, and pyridine to make it undrinkable; used in industries.
- Spurious alcohol: Illicit and toxic alcohol containing methanol; not safe to drink, but used as a solvent in paints and varnishes.
