Physical Properties of Alcohols

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)
Methanol	CH3OH	337.5
Ethanol	C2H5OH	351.5
Propanol	CH3CH2CH2OH	370.0
Butanol	CH3CH2CH2CH2OH	391.0
Pentanol	CH3CH2CH2CH2CH2OH	411.0

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)
CH3CH2OH (Ethanol)	46	351
CH3OCH3 (Methoxymethane)	46	297
CH3Cl (Chloromethane)	50.5	349
CH3CH2CH3 (Propane)	44	231

→ 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

Chemistry Notes