Check sibling questions

Arrange the following in the increasing order of their property indicated (any 2):

(A) Benzoic acid, Phenol, Picric acid, Salicylic acid (pka values).

(B) Acetaldehyde, Acetone, Methyl tert butyl ketone (reactivity towards NH2OH).

(C) ethanol, ethanoic acid, benzoic acid (boiling point)


(A) Picric acid < salicylic acid < benzoic acid <phenol

The pKa value of an acid is inversely dependent on its acidity and/or its stability .

PICRIC ACID - Teachoo.jpg

SALICYLIC ACID - Teachoo.jpg

BENZOIC ACID. - Teachoo.jpg

PHENOL - Teachoo.jpg

The acidity of a compound is directly dependent on the -I effect of the groups attached to the benzene.

  • Since picric acid has 3 -NO 2 groups and an -OH group, the -I effect on benzene is highest. Hence, it has the highest acidity and lowest pKa value.
  • In salicylic acid , there is one -COOH group and an -OH group.
  • In benzoic acid , there is only one -COOH group. Therefore, its pKa value is higher than that of salicylic acid.  
  • Hence phenol has the lowest acidity and highest pKa value due to its single -OH group.

(B) Methyl tert butyl ketone < acetone< Acetaldehyde


ACETONE - Teachoo.jpg

ACETALDEHYDE - Teachoo.jpg

-NH 2 OH would get attached to the carbon that needs an  electron cloud to share most. 

  • The N in -NH 2 OH will share its electrons with the C atom.
  • This means, the chain with the most electronegative C atom will have highest reactivity towards -NH 2 OH

Due the the +I effect of -CH 3 towards the C atom with the ketone group, 


  • Methylterbutylketone, due to its 3 -CH 3   groups , will be least reactive .
  • Acetaldehyde, due to the presence of only one -CH 3 group will be most reactive towards -NH 2 OH.

(C) Ethanol <ethanoic acid < benzoic acid (boiling point of carboxylic acids is higher than alcohols due to extensive hydrogen bonding , boiling point increases with increase in molar mass) 

Boiling point of a substance is the temperature at which force of attraction and bonds between molecules break and allow free movement of molecules.

  • The presence of hydrogen bonds , or higher molecular mass leads to higher boiling points.
  • Since Ethanoic Acid and Benzoic Acid have -COOH groups, they have Hydrogen bonding making them stable.
  • Moreover, the phenyl ring in benzoic acid provides more stability to the compound. 

Hence, Benzoic acid will have the highest boiling point, followed by Ethanoic Acid and then Ethanol.

ETHANOL - Teachoo.jpg

ETHANOIC ACID - Teachoo.jpg

BENZOIC ACID. - Teachoo.jpg

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.