Question

Rank the following acids below from least soluble to most soluble in water. Which acid listed below is the most soluble in water?

Acid Name	Molecular Weight	Melting Point
Cinnamic Acid	148.16	132-33
4-Hydroxyphenylacetic Acid	152.15	148-150
p-Anisic Acid	152.15	183
Hippuric Acid	179.17	188-190
Azelaic Acid	188.22	110
Sebacic Acid	202.25	135

Answer 1

A carboxylic acid with lower molecular weight will form more number of hydrogen bonds with water. Thus it will be more soluble in water.

So among the given acids the increasing order of their solubilities are:

Sebacic acid> Azelaic acid>Hippuric acid> p ansic acid> 4-hydroxyphenyl acetic acid> Cinnamic acid

Among Hippuric acid and 4-hydroxylpehnyl acetic acid, 4-hydroxyphenyl acetic acid has 2 -OH group’s so it will have strong hydrogen bonding than in Hippuric acid.