JEE Challenger
More from p-Block Elements (Group 15-18)
ChemMedAdv 2020 • Paper 1

Reactivity and Properties of Chlorine Oxyanions

With respect to hypochlorite, chlorate, and perchlorate ions, select the valid statement(s):

Options

A

The hypochlorite anion acts as the strongest conjugate base.

Correct
B

The molecular shape of only the chlorate ion is influenced by the lone pair of electrons on Cl.

Correct
C

Hypochlorite and chlorate ions disproportionate to yield identical sets of ions.

D

Hypochlorite ion is capable of oxidizing the sulfite ion.

Correct

Topics & Concepts

p-Block Elements (Group 15-18)p-Block ElementsOxidation State

Step-by-Step Solution

To determine the valid statement(s) regarding hypochlorite (ClO−\text{ClO}^-), chlorate (ClO3−\text{ClO}_3^-), and perchlorate (ClO4−\text{ClO}_4^-) ions, we analyze each option individually:

1. Evaluation of Option (A):

The relative acid strength of the oxoacids of chlorine increases with an increase in the oxidation state of chlorine (or the number of oxygen atoms attached to Cl): HClO<HClO2<HClO3<HClO4\text{HClO} < \text{HClO}_2 < \text{HClO}_3 < \text{HClO}_4

According to Brønsted-Lowry acid-base theory, the weaker the acid, the stronger is its conjugate base. Since HClO\text{HClO} (hypochlorous acid) is the weakest acid among HClO\text{HClO}, HClO3\text{HClO}_3, and HClO4\text{HClO}_4, its conjugate base, ClO−\text{ClO}^- (hypochlorite ion), is the strongest conjugate base among the given set.

Thus, Statement (A) is correct.

2. Evaluation of Option (B):

We apply the Valence Shell Electron Pair Repulsion (VSEPR) theory to determine the influence of lone pairs on the central chlorine atom:

  • Hypochlorite ion (ClO−\text{ClO}^-): It is a diatomic ion consisting of a single Cl−O−\text{Cl}-\text{O}^- bond. Diatomic species possess a fixed linear geometry, so lone pairs do not distort any bond angles.
  • Perchlorate ion (ClO4−\text{ClO}_4^-): The central Cl\text{Cl} atom has 44 σ\sigma-bonds and 00 lone pairs. Its steric number is 44, giving it a symmetric tetrahedral geometry with no lone-pair distortion.
  • Chlorate ion (ClO3−\text{ClO}_3^-): The central Cl\text{Cl} atom has 33 σ\sigma-bonds and 11 lone pair of electrons (Steric number =3+1=4= 3 + 1 = 4). The presence of the lone pair repels the bond pairs, distorting the molecular shape from tetrahedral to trigonal pyramidal.

Thus, only the molecular shape of the chlorate ion (ClO3−\text{ClO}_3^-) is influenced by a lone pair of electrons on the central chlorine atom.

Thus, Statement (B) is correct.

3. Evaluation of Option (C):

Let's consider the disproportionation reactions of hypochlorite and chlorate ions:

  1. Disproportionation of Hypochlorite (ClO−\text{ClO}^-): 3ClO−⟶2Cl−+ClO3−3\text{ClO}^- \longrightarrow 2\text{Cl}^- + \text{ClO}_3^- The resulting set of ions is {Cl−,ClO3−}\{\text{Cl}^-, \text{ClO}_3^-\}.

  2. Disproportionation of Chlorate (ClO3−\text{ClO}_3^-): 4ClO3−⟶Cl−+3ClO4−4\text{ClO}_3^- \longrightarrow \text{Cl}^- + 3\text{ClO}_4^- The resulting set of ions is {Cl−,ClO4−}\{\text{Cl}^-, \text{ClO}_4^-\}.

Since the sets of ions produced in the two disproportionation reactions are different ({Cl−,ClO3−}\{\text{Cl}^-, \text{ClO}_3^-\} vs. {Cl−,ClO4−}\{\text{Cl}^-, \text{ClO}_4^-\}), they do not yield identical sets of ions.

Thus, Statement (C) is incorrect.

4. Evaluation of Option (D):

The hypochlorite ion (ClO−\text{ClO}^-) contains chlorine in the +1+1 oxidation state and acts as a strong oxidizing agent. The sulfite ion (SO32−\text{SO}_3^{2-}) contains sulfur in the +4+4 oxidation state, which readily undergoes oxidation to the +6+6 state (sulfate ion, SO42−\text{SO}_4^{2-}).

The redox reaction is given by: ClO−+SO32−⟶Cl−+SO42−\text{ClO}^- + \text{SO}_3^{2-} \longrightarrow \text{Cl}^- + \text{SO}_4^{2-}

Here, ClO−\text{ClO}^- oxidizes SO32−\text{SO}_3^{2-} to SO42−\text{SO}_4^{2-} while itself being reduced to Cl−\text{Cl}^-.

Thus, Statement (D) is correct.

Conclusion:

The correct statements are A, B, and D.

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