What is Phosphoric Acid? - Structure, Uses & Formula

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Would you ever drink a strong acid? Probably not knowingly, but you almost certainly have already. Curious? Read this lesson on phosphoric acid and its structure, formula, uses, and more.

What Is Phosphoric Acid?

You are composed of all sorts of organic molecules. That doesn't mean those molecules are labeled with a sticker that says 'organic'. It means these molecules contain carbon. But not everything on Earth is organic. Some things lack carbon. Such substances are commonly referred to as being inorganic. One of them is phosphoric acid, a corrosive inorganic acid.

You're about to learn a bit more about its structure, formula, properties and uses.

Structure, Formula, & Properties

Phosphoric acid has alternative names you should be aware of. Some of them include:

  • Orthophosphoric acid
  • Trihydroxidooxidophosphorus
  • o-Phosphoric acid

Its molecular formulas include:

h3po4

This is the most common formula you will see for phosphoric acid and the one you should focus on remembering. A less commonly used formula is:

h3o4p

Note how there is no 'C' for carbon in either formula which means it's an inorganic acid. The 'H' stands for hydrogen, the 'P' stands for phosphorus and the 'O' stands for oxygen.

A 3D representation of phosphoric acids structure using the ball and stick model.
3D

Of course, those are just representations of phosphoric acid. If you were looking at pure phosphoric acid in the lab you'd see a thick, colorless, odorless, and relatively transparent crystalline solid that would only melt at 42.35 C (108.2 F).

When in a less concentrated form, such as 85% aqueous solution, it is a clear, viscous (syrupy), and colorless liquid. These physical properties will all vary depending on the purity and concentration of the substance and the temperature at which you're viewing it.

Uses

Let's see how phosphoric acid is used in the real world. Phosphoric acid is formed when phosphorus is exposed to a flow of warm air. The phosphorus then turns into phosphorus pentoxide. When phosphorus pentoxide is combined with water, it turns into phosphoric acid. Remember, this is a corrosive acid that can damage everything from your body's tissues to metal, so don't handle it unless you know what you're doing!

But, whether you know it or not you have probably eaten something with phosphoric acid in it! Have you ever had a cola? Many soft drinks contain phosphoric acid. Why use phosphoric acid in soft drinks? Well, it gives the drink a slight tart or fruity flavor. The concentration of phosphoric acid in soft drinks is quite low so it's not likely to harm you.

While phosphoric acid is used sparingly in your favorite soda, it is definitely used in large amounts in the field of agriculture. Why? It's used in fertilizers to help plants grow. It is not generally used in its pure form but is used to manufacture various types of safer phosphate fertilizers. Most of the phosphoric acid produced industrially is used for fertilizer production.

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