Alcohols Physical Properties
1. The lower members of alcohols are colourless, volatile liquids with a characteristic alcoholic smell and burning taste whereas higher alcohols are odourless and tasteless.
Higher alcohols having 12 or more carbon atoms are colourless waxy solids.
2. Solubility of alcohols: the first three members are completely miscible with water. The solubility rapidly decreases with increase in molecular mass. The higher members are almost insoluble in water but are soluble in organic solvents like benzene, ether, etc.
The solubility of lower alcohols is due to existence of hydrogen bonds between water and polar O-H group of alcohol molecules.
The solubility of alcohols in water decreases with increase in molecular mass because with increase in molecular mass, the non-polar alkyl group becomes predominant and makes the effect of polar –OH group.
In addition, among the isomeric alcohols the solubility increases with branching of chain. It is because the surface area of non-polar part in the molecule decreases, enhancing the solubility. The argument is well-supported by solubility data of isomeric alcohols, with molecular formula of C4H9OH.
3. Boiling points: boiling points of alcohols are much higher than those of alkenes, haloalkanes or ethers of comparable molecular masses. This is because in alcohols intermolecular hydrogen bonding exists due to which a large amount of energy is required to break these bonds.
Among isomeric alcohols, the boiling point decreases with increase in branching in the alkyl group.
For isomeric alcohols the boiling points generally follow the order:
Primary alcohol > secondary alcohol > tertiary alcohol
4. Lower alcohols are found to form solid derivatives with CaCl2 and MgCl2
It is because of this reason that alcohols cannot be dried with anhydrous CaCl2 and MgCl2
5. Intoxicating effect: alcohols are known to have intoxicating effect. Methanol is poisonous and is not good for drinking purposes. It causes blindness. Ethanol on the other hand is used for drinking purposes. Sometimes it is rendered undrinkable by adding methanol.
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