(i) Write the balanced chemical equation for the reaction of chlorine with hot concentrated sodium hydroxide s

Question 52 of 66

Q. (i) Write the balanced chemical equation for the reaction of chlorine with hot concentrated sodium hydroxide solution. Is this reaction a disproportionation reaction? Justify.

(ii) Give reason for the following:

(x) Why does nitrogen not form a pentahalide although it shows +5 oxidation state? (y) The structure of the XeF2 molecule is linear, not bent.

(iii) Complete the following reaction: P4 (white) + NaOH (conc.) + H2O -> ? (2+2+1)

West Bengal WbchseWest Bengal HS (WBCHSE) Board 2023Subjective· 5mImportance★★★★★

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Hot concentrated NaOH disproportionates Cl2; nitrogen's lack of d-orbitals blocks a pentahalide; XeF2's lone pairs occupy the equatorial plane, leaving a linear axial F-Xe-F; white phosphorus disproportionates in hot NaOH too.

(i) With hot, concentrated NaOH, chlorine disproportionates further than with cold dilute alkali (which stops at hypochlorite):

$3Cl_2 + 6NaOH \xrightarrow{hot,\ conc.} 5NaCl + NaClO_3 + 3H_2O$

This is a disproportionation reaction because the same element, chlorine (oxidation state 0 in Cl2), is simultaneously reduced to Cl- (-1, in NaCl) and oxidised to ClO3- (+5, in NaClO3).

(ii)(x) Nitrogen is in period 2, so its valence shell has only 2s and 2p orbitals available — no d-orbitals. It therefore cannot expand its octet to accommodate 5 bond pairs (10 electrons), so NCl5/NF5-type pentahalides are not possible; phosphorus, with accessible 3d orbitals, can form PCl5.

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set A1 markMCQ
$Q. Which of the following is the strongest base ?$
(a) ClO4^-
(b) ClO3^-
(c) ClO2^-
(d) ClO^-
›Reveal solutionSolution

The oxoacid strength order is HClO4 > HClO3 > HClO2 > HClO, so the conjugate base of the weakest acid, ClO^-, is the strongest base.

For chlorine oxoacids, acid strength increases with the number of oxygen atoms (more oxygens stabilise the anion by spreading the negative charge):

HClO4 > HClO3 > HClO2 > HClO (decreasing acid strength)

…

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CBSE 2026Set SEM31 markMCQ
$Q. Which one of the following is strongest acid?$
(a) HOCl
(b) HClO2
(c) HClO4
(d) HClO3
›Reveal solutionSolution
Acid strength of chlorine oxoacids rises with the number of terminal O atoms / oxidation state of Cl: HOCl < HClO2 < HClO3 < HClO4. Correct option (c).

For oxoacids of the same central halogen, acid strength increases as more oxygen atoms are attached, because they withdraw electron density and stabilise the conjugate base (anion) by spreading the negative charge over more oxygens.

HOCl (Cl = +1) weakest

HClO2 (Cl = +3)

HClO3 (Cl = +5) …
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CBSE 2025Set ANNUAL1 markMCQ
$Q. Which of the following acids is most acidic in nature?$
(a) HClO
(b) HClO2
(c) HClO4
(d) HClO3
›Reveal solutionSolution
Acid strength of chlorine oxoacids increases with the number of oxygen atoms bonded to chlorine: $HClO < HClO_2 < HClO_3 < HClO_4$ .

All four acids have the general form $HOClO_n$ with the ionisable proton on an oxygen bonded to Cl. As the number of oxygen atoms attached to the central Cl atom increases:

The oxidation state of Cl increases (+1 in HClO, +7 in $HClO_4$ ), so Cl pulls electron density more strongly (higher effective electronegativity / -I effect), weakening the O-H bond and making the proton easier to release. …
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CBSE 2022Set E1 markMCQ
$Q. Which of the following forms only one oxyacid ?$
(a) F2
(b) Cl2
(c) Br2
(d) I2
›Reveal solutionSolution

Fluorine is the most electronegative element and shows only the -1 (and 0) state, so it forms just one oxyacid, HOF.

Because fluorine is more electronegative than oxygen, it cannot take a positive oxidation state in an oxyacid; it forms only hypofluorous acid, HOF, where fluorine is still effectively in a -1 state. Thus F2 gives only one oxyacid.

…

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CBSE 2021Set A1 markMCQ
$Q. The strongest acid is$
(a) HClO4
(b) HClO3
(c) HClO2
(d) HClO
›Reveal solutionSolution

Among HClO, HClO2, HClO3, HClO4, acidity increases with the number of non-hydroxyl (terminal) oxygens, so HClO4 is strongest.

For the oxoacids of chlorine, acid strength increases as the oxidation state of chlorine (and the number of terminal oxygen atoms) increases. More terminal O atoms withdraw electron density and stabilise the conjugate base by spreading the negative charge (reson …

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Q.(i) Write the balanced chemical equation for the reaction of chlorine with hot concentrated sodium hydroxide solution. Is this reaction a disproportionation reaction? Justify.

Concept understanding — Oxoacids of Halogens

Q.(i) Write the balanced chemical equation for the reaction of chlorine with hot concentrated sodium hydroxide solution. Is this reaction a disproportionation reaction? Justify.

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