Ncert Exercises & Solutions

Q. 25 Name the factors responsible for the solubility of alcohols in water.

Solubility of alcohols in water depends upon the two factors.

(i) Hydrogen bonding Higher the extent of hydrogen bonding, higher is the solubility. The hydrogen group of alcohol form hydrogen bonding, Solubility increases with increase in the number of — OH groups in alcohols of comparable molecular masses.

$H_{3} C - {CH}_{2} - {CH}_{2} - OH < {CH}_{3} - \underset{|}{C}$
$OH H - {CH}_{2} - OH$
$(I) (II)$

(I) Compound (II) will form stronger H-bond due to two — OH group and hence has higher boiling point.

(ii) Size of alkyl/aryl group Higher the size of alkyl/aryl group (hydrocarbon part), lower is the extent of hydrogen bonding and lower is the solubility. Hence,

$H_{3} C - {CH}_{2} - OH > {CH}_{3} {CH}_{2} - {CH}_{2} OH > {CH}_{3} {CH}_{2} {CH}_{2} - {CH}_{2} OH$

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