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Solubility of Alcohols

January 21, 2013

Alcohols are compounds having hydroxy group directly bonded to a saturated carbon atom, having the general formula R–OH. ‘R’ can be (i) aliphatic saturated – ethyl alcohol (ii) unsaturated – allyl alcohol (iii) aralkyl – benzyl alcohol. A compound can have more than one hydroxy group such as ethylene glycol, a dihydric alcohol and
CH2– CH2
|         |
OH     OH
Glycerol a trihydric alcohol. CH2– CH – CH2
|        |           |
OH   OH       OH

 

Alcohols can be further classified as primary, secondary and tertiaryaccording to the kind of carbon to which the –OH group is linked. Primary alcohols having OH group attached to a carbon which is attached to only one carbon atom, secondary alcohol are compound wihch as got the OH group attached to the carbon which is attached to two other carbon atom, while tertiary alcohols are those which has OH attached to the carbon which is attached to three carbon atoms. Let see the solubility of alcohols in water.

Solubility of Alcohols in Water

Alcohols are neutral substances whereas inorganic hydroxides are basic in nature. Physical properties of an alcohol are best understood if we recognise that structurally an alcohol is a composite of an alkane and water. The properties are intermediate between the water and the parent alkane which it is composed off. Alcohols are soluble in water and other hydroxy compounds in contrast to hydrocarbons. Methanol and Ethanol are miscible in water in all proportions. This is also explained on the basis of intermolecular hydrogen bonding.  Since alcohol and water are polar compound  they are miscible with each other.  The energy required to break intermolecular forces between alcohol molecules is provided by the formation of hydrogen bond between a water molecule and an alcohol molecule. Lower members are completely miscible with water and the solubility decreases with increase in molecular weight. This decrease in solubility is because of the increase in size of the hydrophobic alkyl group in the alcohol.

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