The Valence of Phosphorus in Common Hypophosphites

Common phosphorus-containing compounds include hypophosphites, phosphites, and orthophosphates. Each category has a different phosphorus content, and therefore a different valence. Generally, the valences are +1 (sodium hypophosphite), +3 (sodium phosphite), and +5 (trisodium phosphate). Why do these different valence states occur? Below, we will compare the valences of phosphorus in several hypophosphites to clarify this.

1. Hypophosphites

Sodium hypophosphite (NaH2PO2) and hypophosphite (H3PO2) have strong reducing properties. Their phosphorus valence is +1, indicating strong antioxidant capacity. For example, in NaH2PO2, Na: +1, H: +1, and therefore the phosphorus valence is +1, resulting in a very high redox potential. Naturally, its reducing power is very strong.

2. Phosphites

This category of products generally has some reducing properties. Representative products include phosphorous acid, potassium phosphite, and sodium phosphite. For example, consider Na2HPO3, where Na: +1, H: +1. Since the sum of positive and negative potentials equals 0, the oxidation state of phosphorus in Na2HPO3 is +3. Therefore, the oxidation state of phosphorus in phosphite is lower than that in orthophosphate, exhibiting some reducing properties. It requires oxidizing conditions to form +5 phosphorus.

3. Orthophosphates

Main products include phosphoric acid, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, trisodium phosphate, etc. For example, potassium dihydrogen phosphate (KH2PO4), where K: +1, H: +1, O: -2, calculates that P is +5. Therefore, the oxidation state of phosphorus in orthophosphate is +5. It does not have reducing properties.

Phosphates have high phosphorus oxidation states and do not have reducing properties. Sodium phosphite and sodium hypophosphite have lower phosphorus oxidation states than other phosphates and exhibit strong reducing properties.