Physical Properties of Alcohols Preparation and Properties
Physical State :
→ First three members of alcoho1 family CH3OH, C2H5OH and C3H7OH are colourless liquids with alcoholic smell.
C4H9OH to C11H23OH are liquids.
→ Alcohols containing 12 or more than 12 carbon atoms are colourless waxy solids.
→ Alcohols are almost neutral.
→ BoilIng Points : The B.P. of alcohols are higher than alkanes, alkenes, alkynes. ethers, alkyl halides, carbonyl compounds of almost same molecular masses, because of molecular association due to intermolecular H-bonding between molecules of alcohols so more heat is required to separate associated molecules, therefore the boiling points of alcohols are higher.
→ The lower members have low boiling points with increase in molecular maps, the boiling points keep on increasing gradually because of increase in vander Wall’s forces.
B.P. ∝ Molecular mass vander Wall’s forces
→ If branching of carbon chain increased it decreases boiling point of alcohol because of decrease in surface area.
Table 11.2 Boiling points of some alcohols.
|Name||Formula||Boiling Point (k)|
Table 11.3 : Boiling points of isomeric butanols:
Table 11.4. Boiling points of alcohols and compounds having comparable molecular masses
|Compound||Molecular Mass||Boiling point (K)|
→ Alcohols are hypnotic or narcotic in nature. Ethanol relaxes the central nervous system and cause unconsciousness. The use of methanol in small amount can causes blindness. Tertiary alcohol is used as hypnotic and transquiizer because its hypnotic effect is more.
→ Solubility : The lower members are highly soluble in water due to their ability to form hydrogen bonds with water molecules. The solubility decreases with increase in size of alkyl groups of alcohol. The solubility increases with increase in branching ofisomeric alcohols. As the number of branches increases the surface area of non-polar hydrocarbon part decreases and hence solubility in water increases.
→ Toxio Nature : Alcohols are toxic in nature. Methanol is highly poisonous and is not good for drinking purposes. It causes blindness. On the otherhand ethanol has intoxicating effect and hence is widely used for drinking purposes.
→ Lower Alkanols form solid derivatives with some specific metallic salts. For example.
- CuSO4 . 2CH3OH
CuSO4 . 2C2H5OH
- CaCl2 . 4CH3OH
CaCl2 . 4C2H5OH
- MgCl2 . 6CH3OH
MgCl2 . 6C2H5OH