Explain why hypophophorous acid acts as reducing agent but phosphoric acid does not?

Answer 1

H3PO4, phosphorous acid, is the most stable form of a __phosphor___ acid

In H3PO4 H3 = +3, P = __ O4 = -8

In H3PO4 the charge on P = +5

The 4 O atoms have attracted 5 electrons from the P atom.

These were the 3s2, 3p3 electrons, leaving the P atom with 2s2, sp8, an octet, a stable state.

Hypophosphoric acid = H3PO2

In H3PO2, H3 =+3, P = ___, O2 = -4

In H3PO2, the charge on P = +1

One of the O atoms has attracted 1 electron from the P atom.

This electron came from were the 3s2, 3p3 electrons, leaving the P atom with 3s2, 3p2 an unstable state.

The P atom in H3PO2 needs to lose the 4 electrons, 3s2, 3p2, to be stable. This means the H3PO2 is oxidized, as it reduces a nonmetal such as I2.

Phosphoric acid removes the zinc coating from roofing nails. It is an ingredient in Toilet bowl cleaner.

The reaction equation is ;

Zn + H3PO4 à + Zn3(PO4)2 + H2

Zn = 0 charge is oxidized to Zn +2 charge in the Zn3(PO4)2; as H+1 charge in the H3(PO4)3 is reduced to H = 0 charge in H2. The H2 is the oxidizing agent, and the Zn is the reducing agent.

The H in the Phosphoric acid causes Zinc to be oxidized from Zn = 0 charge to Zn = +2 charge. Thus Phosphoric acid provides an oxidizing agent.

Answer 2

Hypophosphorous acid (H3PO2) has a lower oxidation state of phosphorus (+1) compared to phosphoric acid (H3PO4) which has a higher oxidation state of phosphorus (+5). Compounds with lower oxidation states are more easily oxidized and therefore act as reducing agents, while those with higher oxidation states do not readily give up electrons and therefore do not act as reducing agents.

Answer 3

Because in H3PO4 oxidation state of P is +5 which is highest for P. Therefore cant act as reducing agent.