Good reducing nature of H3PO2 is attributed to the presence of
(a) two P-H bonds
(b) one P-H bond
(c

Q: Why doesn't the P-OH bond act as a reducing agent?

The oxygen atom in the P-OH bond is highly electronegative. It holds onto the hydrogen atom tightly, making it acidic (capable of releasing $H^+$) rather than hydridic (capable of acting as a reducing agent).

Q: What is the oxidation state of phosphorus in $H_3PO_2$?

Let's calculate it: $3(+1) + x + 2(-2) = 0$. Solving this gives $x = +1$. Phosphorus is in a +1 oxidation state, which is quite low, allowing it to be easily oxidized to +5.

Q: How does $H_3PO_2$ compare to $H_3PO_3$ in terms of reducing power?

$H_3PO_2$ is a stronger reducing agent than $H_3PO_3$. This is because $H_3PO_2$ has two P-H bonds, whereas $H_3PO_3$ only has one P-H bond.

Q: Is $H_3PO_2$ a strong acid since it has three hydrogen atoms?

No, it is a weak, monobasic acid. Only the hydrogen atom attached to the highly electronegative oxygen atom (in the P-OH group) is ionizable. The two hydrogens attached directly to phosphorus are not ionizable.

Q: Why is the P-H bond considered 'hydridic'?

Although phosphorus and hydrogen have similar electronegativities, in the context of these oxoacids, the P-H bond can be broken during oxidation-reduction reactions, effectively transferring electrons to another species, which is the hallmark of a reducing agent.

Question

Good reducing nature of $H_3PO_2$ is attributed to the presence of

Options:

(A) two P—H bonds

(B) one P—H bond

(C) two P—OH bonds

(D) one P—OH bond

Sigma Percentile · Accepted Answer

### The Secret Behind the Reducing Power of Hypophosphorous Acid

When we dive into the chemistry of phosphorus oxoacids, one molecule often stands out for its aggressive chemical behavior: **hypophosphorous acid**, chemically known as $H_3PO_2$.

To truly understand why this molecule acts the way it does, we must look beyond its chemical formula and examine its structural anatomy. The secret to its reactivity is entirely hidden in how its atoms are connected.

### The Structural Revelation

Let's visualize the structure of $H_3PO_2$. At the heart of the molecule sits a central phosphorus (P) atom. This central atom is bonded to its surrounding atoms in a very specific tetrahedral-like arrangement.

First, it forms a strong double bond with one oxygen atom ($P=O$). Next, it forms a single bond with a hydroxyl group ($P-OH$). Finally, and most importantly, it forms two direct single bonds with hydrogen atoms ($P-H$).

It is these direct **$P-H$ bonds** that dictate the molecule's destiny as a reducing agent.

### The Chemistry of Reduction

In the world of phosphorus oxoacids, the rule of thumb is simple: **the reducing nature of the acid is directly proportional to the number of $P-H$ bonds it possesses**.

Why is this the case? The hydrogen atoms directly attached to the phosphorus atom are uniquely positioned to be oxidized. During a chemical reaction, these $P-H$ bonds can be broken, allowing the molecule to transfer electrons to another species, thereby reducing it.

Because $H_3PO_2$ boasts exactly **two $P-H$ bonds**, it acts as a remarkably strong reducing agent. We can see this power in action when it reacts with silver nitrate ($AgNO_3$):

$$4AgNO_3 + H_3PO_2 + 2H_2O \rightarrow 4Ag\downarrow + H_3PO_4 + 4HNO_3$$

In this reaction, $H_3PO_2$ effortlessly reduces the silver ions ($Ag^+$) down to solid metallic silver ($Ag$), while it gets oxidized into phosphoric acid ($H_3PO_4$).

### Conclusion

Therefore, the exceptional reducing nature of $H_3PO_2$ is not due to its $P-OH$ bonds, but entirely attributed to the presence of its **two $P-H$ bonds**.

As a quick mental check for future problems, always remember the order of reducing power among phosphorus oxoacids: $H_3PO_2$ (two $P-H$ bonds) > $H_3PO_3$ (one $P-H$ bond) > $H_3PO_4$ (zero $P-H$ bonds).

Animated Solution for Chemistry - s and p-Block Elements: Good reducing nature of $H_{3} P O_{2}$ is attributed to the presence of

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Visualized Solution

\text{Structure of } H_3PO_2

\text{Bonds in } H_3PO_2

\text{Reducing Nature}

\text{Counting P-H Bonds}

\text{Chemical Proof}

\text{Conclusion}

\text{The Way Forward}

The Sigma Insight: Group 15 Elements

The Secret Behind the Reducing Power of Hypophosphorous Acid

The Structural Revelation

The Chemistry of Reduction

Conclusion

Similar Questions

The correct statement(s) related to oxoacids of phosphorous is(are)

The compound(s) with P–H bond(s) is(are)

The order of the oxidation state of the phosphorus atom in $H_{3} PO_{2}$ , $H_{3} PO_{4}$ , $H_{3} PO_{3}$ and $H_{4} P_{2} O_{6}$ is

The pair that contains two P—H bonds in each of the oxoacids is

The number of hydrogen atom(s) attached to phosphorus atom in hypophosphorous acid is

The oxidation states of 'P' in $H_{4} P_{2} O_{7}$ , $H_{4} P_{2} O_{5}$ and $H_{4} P_{2} O_{6}$ , respectively are

The number of ionisable hydrogens present in the product obtained from a reaction of phosphorus trichloride and phosphonic acid is

In a molecule of pyrophosphoric acid, the number of $P—OH$ , $P = O$ and $P—O—P$ bonds/moiety(ies) respectively are

Which one of the following group-15 hydride is the strongest reducing agent ?

Which of the following statements is true ?

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