JEE Main 2021
LEVELJEE Advanced
Visualized Solution
The Sigma Insight: Group 15 Elements
The Chemical Encounter
Imagine you are in a laboratory, mixing two fascinating compounds: phosphorus trichloride () and phosphonic acid ().
Phosphonic acid is more commonly known to students as phosphorous acid.
When these two react in the presence of moisture, a beautiful condensation-like process occurs.
The primary product of this reaction is a new, larger molecule called pyrophosphorous acid ().
Our mission is to uncover the hidden secrets of this molecule, specifically, how many of its hydrogen atoms are willing to detach and act as acids.
Decoding the 'Pyro' Structure
To understand the behavior of pyrophosphorous acid, we must first visualize its molecular architecture.
The prefix 'pyro' is a massive hint. It tells us that two molecules of the parent acid have joined together by sacrificing a water molecule.
This leaves us with two central phosphorus atoms connected by a single oxygen bridge ().
Next, to satisfy the valency and create a stable oxoacid, each phosphorus atom forms a strong double bond with an oxygen atom ().
The Trap of the Non-Polar Bond
Now, we have four hydrogen atoms left to place, and this is where many students fall into a classic trap.
We must attach one hydrogen atom directly to each phosphorus atom.
The electronegativity of phosphorus (2.19) and hydrogen (2.20) are nearly identical.
Because of this, the bond is essentially non-polar.
A hydrogen atom needs a highly polar bond to be stripped away as a proton (). Therefore, these directly attached hydrogens are strictly non-ionisable.
The Final Count
We are left with two oxygen atoms and two hydrogen atoms.
These naturally pair up to form two hydroxyl groups (), which attach to the remaining valencies on the phosphorus atoms.
For a hydrogen to be ionisable, it must be bonded to a highly electronegative atom like oxygen.
Looking at our completed structure, we can clearly see exactly two groups.
This means that out of the four hydrogens in the molecule, only two have the ability to ionise.
Thus, the number of ionisable hydrogens in pyrophosphorous acid is 2.
Similar Questions
LEVELJEE Main
The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is
(A)
three
(B)
one
(C)
two
(D)
zero
JEE Main 2020
LEVELJEE Main
In a molecule of pyrophosphoric acid, the number of , and bonds/moiety(ies) respectively are
(A)
2, 4 and 1
(B)
3, 3, and 3
(C)
4, 2, and 0
(D)
4, 2, and 1
JEE Main 2020
LEVELJEE Main
White phosphorus on reaction with concentrated NaOH solution in an inert atmosphere of gives phosphine and compound (X). (X) on acidification with HCl gives compound (Y). The basicity of compound (Y) is
(A)
4
(B)
3
(C)
2
(D)
1
JEE Advanced 2025
LEVELJEE Main
The compound(s) with P–H bond(s) is(are)
* Multiple Correct Options
(A)
(B)
(C)
(D)
JEE Advanced 2021
LEVELJEE Main
The correct statement(s) related to oxoacids of phosphorous is(are)
* Multiple Correct Options
(A)
Upon heating, undergoes disproportionation reaction to produce and .
(B)
While can act as reducing agent, cannot.
(C)
is a monobasic acid.
(D)
The H atom of P–H bond in is not ionizable in water.
JEE Advanced 2023
LEVELJEE Advanced
Match the reactions (in the given stoichiometry of the reactants) in List-I with one of their products given in List-II and choose the correct option.
JEE Main 2019
LEVELJEE Main
Good reducing nature of is attributed to the presence of
(A)
two P—H bonds
(B)
one P—H bond
(C)
two P—OH bonds
(D)
one P—OH bond
JEE Advanced 2014
LEVELJEE Main
The product formed in the reaction of with white phosphorous is
(A)
(B)
(C)
(D)
JEE Advanced 2017
LEVELJEE Main
The order of the oxidation state of the phosphorus atom in , , and is
(A)
(B)
(C)
(D)
JEE Main 2021
LEVELJEE Main
The oxidation states of 'P' in , and , respectively are
(A)
and
(B)
and
(C)
and
(D)
and