Phosphorous acid

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Phosphorous acid is a chemical compound with the formula H₃PO₃. This compound is a diprotic acid, which means it can donate two protons (H⁺ ions) in an aqueous solution. Phosphorous acid is an important intermediate in the preparation of other phosphorus compounds.

Chemical Structure and Properties

Phosphorous acid has the molecular formula H₃PO₃ and is also known as orthophosphorous acid. The structure of phosphorous acid consists of one phosphorus atom bonded to three hydrogen atoms and one oxygen atom, with one of the hydrogen atoms directly bonded to the phosphorus atom, making it a diprotic acid. The chemical structure can be represented as HPO(OH)₂.

Preparation

Phosphorous acid can be prepared by the hydrolysis of phosphorus trichloride (PCl₃) with water:

PCl₃ + 3 H₂O → H₃PO₃ + 3 HCl

Reactions

Phosphorous acid is a reducing agent and can be oxidized to phosphoric acid (H₃PO₄). It can also react with bases to form phosphite salts. For example, with sodium hydroxide (NaOH), it forms sodium phosphite (Na₂HPO₃):

H₃PO₃ + 2 NaOH → Na₂HPO₃ + 2 H₂O

Uses

Phosphorous acid is used in various applications, including:

• As a reducing agent in chemical synthesis.
• In the production of phosphite salts, which are used as fungicides.
• As an intermediate in the manufacture of other phosphorus-containing compounds.

Safety and Handling

Phosphorous acid is corrosive and can cause burns upon contact with skin or eyes. It should be handled with appropriate safety precautions, including the use of personal protective equipment.

Related Compounds

• Phosphoric acid
• Phosphorus trichloride
• Phosphite

See Also

• Phosphorus
• Acid
• Reducing agent