JEE Advanced 2023 Paper 1 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium

Consider the oxoacids of phosphorus: H3PO2, H3PO3, H3PO4, H4P2O5 (pyrophosphorous acid), H4P2O6 (hypophosphoric acid) and H4P2O7 (pyrophosphoric…

Numerical answer

Consider the oxoacids of phosphorus:

\mathrm{H_3PO_2}

\mathrm{H_3PO_3}

\mathrm{H_3PO_4}

\mathrm{H_4P_2O_5}

(pyrophosphorous acid),

\mathrm{H_4P_2O_6}

(hypophosphoric acid) and

\mathrm{H_4P_2O_7}

(pyrophosphoric acid). Let

x

be the number of these acids containing at least one

\mathrm{P\!-\!H}

bond,

y

the number containing a

\mathrm{P\!-\!O\!-\!P}

linkage and

z

the number containing a direct

\mathrm{P\!-\!P}

bond. The value of

x+y+z

Show answer and solution

Answer: 6

Structures:

\mathrm{H_3PO_2}

\mathrm{H_2P(O)(OH)}

, two

\mathrm{P-H}

;

\mathrm{H_3PO_3}

\mathrm{HP(O)(OH)_2}

, one

\mathrm{P-H}

;

\mathrm{H_3PO_4}

\mathrm{P(O)(OH)_3}

, none;

\mathrm{H_4P_2O_5}

\mathrm{(HO)(H)P(O)-O-P(O)(H)(OH)}

with two

\mathrm{P-H}

and a

\mathrm{P-O-P}

bridge;

\mathrm{H_4P_2O_6}

\mathrm{(HO)_2P(O)-P(O)(OH)_2}

with a

\mathrm{P-P}

bond;

\mathrm{H_4P_2O_7}

\mathrm{(HO)_2P(O)-O-P(O)(OH)_2}

with a

\mathrm{P-O-P}

bridge.

x

= acids with

\mathrm{P-H}

\mathrm{H_3PO_2},\mathrm{H_3PO_3},\mathrm{H_4P_2O_5}

\Rightarrow x=3

y

= acids with

\mathrm{P-O-P}

\mathrm{H_4P_2O_5},\mathrm{H_4P_2O_7}

\Rightarrow y=2

z

= acids with

\mathrm{P-P}

\mathrm{H_4P_2O_6}

\Rightarrow z=1

.
Therefore

x+y+z=3+2+1=6

. Note that

\mathrm{H_4P_2O_5}

is counted in both

x

and

y

Original question written in the JEE Advanced 2023 Paper 1 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake