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Q97 (CDS-I/2003) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

Consider the following 0.1 N acids: I. Acetic acid II. Perchloric acid II, Chloroacetic acid IV. Hydrochloric acid What is the sequence of these in terms of their increasing acid strength in water?

Result
Your answer: —  Â·  Correct: A
Explanation

The acid strength in water is determined by the degree of dissociation and the stability of the resulting conjugate base. Acetic acid (CH3COOH) is a weak organic acid with a pKa of approximately 4.76 [1]. Chloroacetic acid (ClCH2COOH) is stronger than acetic acid because the electronegative chlorine atom exerts an inductive effect (-I effect), stabilizing the carboxylate anion and lowering the pKa to about 2.86. Hydrochloric acid (HCl) and perchloric acid (HClO4) are both strong mineral acids that dissociate almost completely in water [1]. However, perchloric acid is considered the strongest known mineral acid due to the high oxidation state of chlorine and the resonance stabilization of the perchlorate ion, making it stronger than HCl [t1]. Therefore, the increasing order of acid strength is Acetic acid < Chloroacetic acid < Hydrochloric acid < Perchloric acid (I < III < IV < II).

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? > p. 26
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