Hypophosphoric Acids – Uses, Preparation, Properties and Side Effects

What is an Acid?

An acid is a chemical substance that donates protons or hydrogens ions to accept electrons. Acids taste sour and change blue litmus paper into red, it also has the ability to react with metals to release hydrogen, and bases to form salts.

Examples of acids are hydrochloric acid, nitric acid, citric acid, acetic acid, hypophosphoric acid, sulfonic acids, carboxylic acids etc.

What are Hypophosphoric Acids?

Hypophosphoric acids also called phosphonic acids are acids with an oxidation state of +4. These acids are chemical represented as H4P2O6. They contain 4 hydrogens, 2 phosphorus and 6 oxygen atoms.

Structure of Hypophosphoric Acids

As earlier stated, hypophosphoric acids contain 4 hydrogens, 2 phosphorus and 6 oxygen. These atoms make up the structure of hypophosphoric acid. 

Hypophosphoric acids are made up of P-P bonds that contain 2(P-OH) bonds and 1(P-O) bond. The bond length for the P-P bond is 219pm and that of the P-OH is 151pm.

Preparation of Hypophosphoric Acids

Hypophosphoric acids are prepared using hydrolysis and oxidation methods.


Hydrolysis is defined as the reaction of an organic chemical with water to form two or more new substances.


Oxidation is defined as the loss of electrons during a reaction by a molecule, atom or ion. The preparation of hypophosphoric acid is done at room temperature. Red phosphorus are combined chemically with sodium chlorite to produce hypophosphoric acid.

2P + 4NaOCl2 + 2H2O  ⇢  H4P2O6 + 2 NaCl

Properties of Hypophosphoric Acids

Physical and Chemical Properties of Hypophosphoric Acids

A physical property is referred to as any property that is measurable and whose value describes the state of a physical system while a chemical property is a characteristic of a particular substance that can be observed in a chemical reaction. The following are the physical and chemical properties of hypophosphoric acid.

Appearance Hypophosphoric acids appear as a white solid in a dihydrate state and has no odour.
Other Names Another name for hypophosphoric acid is diphosphoric acid.
Melting Point  Hypophosphoric Acids have a melting point of 54°C.
Solubility Hypophosphoric acids are soluble in alcohol and ether and miscible in water.
Molar Mass Hypophosphoric acids have a molar mass of 161.98 g/mol as a white crystalline powder.
Acidity Hypophosphoric acids have an acidity of 1.2.
Density The density of hypophosphoric acid is 1.493 g/cm3

1.22 g/cm3 (50 wt% aq. solution)

Uses of Hypophosphoric Acids 

Hypophosphoric acids have a wide range of uses/applications. These are some of the uses of hypophosphoric acids.

  1. It can be used as a reducing agent and a bleaching agent. 
  2. It can also be used as a stimulant in pharmaceuticals.
  3. Chemically, it has wide applications as it can be used as tetrabasic acid, and wetting agents. 

Side Effects of Hypophosphoric Acids 

Hypophosphoric acid is known as a highly corrosive substance. Here are some of the side effects of hypophosphoric acids.

  1.  Chemical burns to the skin and eyes are possible when in contact with this acid. 
  2. It may cause irritation in the upper respiratory system if inhaled into the nostrils. 
  3. Irritation of the eye and eyelids are possible.

Precautions to Take While Handling Hypophosphoric Acids 

  1. Wash with running water when it gets into the eyes. 
  2. Do not swallow because it will harm the mucous lining of the mouth, as well as the throat, oesophagus, and stomach.
  3. Wear googles to protect your eyes when working with this chemical. 
  4. Avoid breathing in vapours, mist or gas and ensure there is adequate ventilation in the lab.


How is Hypophosphoric Acid formed?

Hypophosphoric acid is prepared by the hydrolysis and oxidation of red phosphorus by NaOCl (sodium hypochlorite), or white phosphorus by water and air.

What is the basicity of this compound “Hypophosphoric Acid”?

The basicity of hypophosphorous acid is 1, because only one hydrogen atom is bonded to the electronegative atom, oxygen.

What are the uses of  Hypophosphoric Acids?

Hypophosphorous acids are used by large industries as bleaching, color stabilization or decoloring agents for plastics, synthetic fibers and chemicals.

Can Hypophosphoric Acids act as reducing agents?

The answer is yes. Hypophosphoric acid is a phosphorus oxyacid and a powerful reducing agent with a molecular formula of H3PO2. It is commonly used to eliminate Cu, Hg and Ag and to test impurities like Nb, As and Ta, etc.