Question

Which of the following will not react with $NaOH$ to form water?

• A. $Na{H}_{2}P{O}_3$
• B. $N{a}_{2}HP{O}_3$
• C. $Na{H}_{2}P{O}_2$
• D. $N{a}_{2}HP{O}_4$

Answer 1

Answer: (B), (C)

The correct options are
B $N{a}_{2}HP{O}_3$
C $Na{H}_{2}P{O}_2$


(Mono)sodium salt of (I) will not react with $O{H}^{\ominus }$ to give water. This is clear looking at the structure of (I) where the remaining hydrogens (after substitution), are directly bonded to the phosphorus atom. But the monosodium salt of (II) and (III) will react with $O{H}^{\ominus }$ to give water because there are acidic protons present.

Disodium salt of (II) will not react with $O{H}^{\ominus }$ to give water. There won't be an acid base reaction because the lone $H$ is directly bonded to the phosphorus atom. But the disodium salt of (III) will take part in an acid-base reaction with $O{H}^{\ominus }$ to yield water.