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Phosphoric Acid Uses

Last updated date: 20th Apr 2024
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An Introduction to Phosphoric Acid and its Uses

Inorganic acids are found naturally in nature and also synthesized in laboratories. As you have studied, the non-metallic oxides generally form an acid when dissolved in water. Today, you will learn more about Phosphoric Acid (H3PO4) and phosphoric acid uses in this article in an elaborate way. Concentrate on the molecular formula of the acid and learn how this inorganic acid is used in different ways. You will also learn the phosphoric acid health effects along with its physical and chemical properties.

Phosphoric acid: A Short Introduction

As mentioned earlier, there are many inorganic acids in nature. We have learned about these acids by identifying the elements and doing a lot of research. One such fascinating acid is phosphoric acid. It is a tribasic acid due to its formula (H3PO4).

The word ‘tribasic’ depicts that one molecule of this acid contains three replaceable hydrogen atoms. It means that it can create three different kinds of salt when reacting with a base due to its tribasic nature. Due to the partial displacement of the hydrogen atoms in its molecule, it can create acidic salts (salts with replaceable hydrogen atoms). The valency of the central element that is phosphorus is 5. This is why it is also called orthophosphoric acid or phosphoric (V) acid. You can easily understand the H3PO4 acid name and answer the questions.

Physical Properties of Phosphoric Acid

  • This acid is odourless, colourless, and viscous in nature. In solid form, it crystallizes very quickly by strongly holding onto the water molecules. In fact, you will be astonished to know that this acid cannot be separated from water molecules. Hence, in concentrated form, it exists like a syrupy colourless liquid.

  • It turns blue litmus red due to its acidic nature.

  • This acid turns into a glass-like transparent yet brittle substance when brought close to a red hot heat source.

  • The molecular weight of this acid is 97.994 gram/mol

  • The density of this acid is 1.88 g/cc

  • It boils at a temperature of 158 °C and melts at a temperature of 42.35 °C.

Chemical Properties of Phosphoric Acid

As mentioned earlier, this acid has an excellent affinity to water. Hence, it is a deliquescent substance and tends to absorb moisture from the air. It also forms a syrupy aqueous solution when comes in contact with water.

It is not as strong as sulphuric or nitric acid but shows acidity in presence of an indicator. It also goes through acid-base reactions but not as fast or vigorously as the mentioned inorganic acids.

  • It shows three dissociation steps in an aqueous solution. Hence, it can produce three different types of salts. Two of these salts with a base will have acidic properties due to the presence of a hydrogen atom.

  • Phosphoric acid is used in different industries and also as an excellent pH buffer system. Its sodium salts act as pH buffering agents.

Different Types of Phosphoric Acids

Due to the variable valency of phosphorus, the central element, there are different types of phosphoric acid existing in nature or can be synthesized in the labs. Let us take a quick look at the molecular formula of these acids.

  • Hypophosphorous Acid

The valency of phosphorus in this acid is 1 and its molecular formula is H3PO2. Its basicity is 1

  • Phosphorus Acid

The valency of the central element is 3 and its basicity is 2. The molecular formula is H3PO3.

  • Orthophosphoric Acid

The valency of the central element is 5 and the basicity of this acid is 3. The molecular formula of this acid is H3PO4.

  • Pyrophsophoric Acid

The valency of the central element is 5 and the basicity of this acid is 4. Its molecular formula is H4P2O7.

  • Metaphosphoric Acid

The valency of the central element is 5 and the basicity of this acid is 1. Its molecular formula is HPO3.

Uses of Phosphoric Acid

As phosphoric acid and phosphoric salts are not that harmful and can be used as a buffer, you will find myriads of their uses. Let us discuss them briefly here.

  • To Remove Rust

This acid is popularly used to remove rust without hampering the integrity of the iron utensils and equipment. Rust chemically transforms from ferric oxide to ferric phosphate and blackens in colour. It is then removed easily.

  • Edible Items

The pH buffering properties of this acid and its salt is also used in making food items and beverages. In fact, its acidity regulation property is used to manufacture edibles such as processed meat, cereal bars, jams, cheese, etc. It stops the formation of germs and increases the shelf life of the products.

  • Personal Care

One of the prime phosphoric acid uses is in personal care product development. It is used in formulating dyes, makeup, skincare, fragrances, bath salts, cleaning products, etc.

  • Agriculture

The phosphoric acid uses in agriculture is quite huge as nearly 80% of the total volume of this acid manufactured is used in making fertilizers.


Although phosphoric acid health effects are not that prominent, they can still cause harm to your sensitive organs at a high concentration. This acid is exceptionally used in different industries for various purposes.

FAQs on Phosphoric Acid Uses

1. Why is Phosphoric Acid Called a Tribasic Acid?

The acid has three replaceable hydrogen atoms in one molecule. All these atoms can be replaced by an alkali to form three different kinds of salts. This is why phosphoric acid is tribasic.

2. Why is Phosphoric Acid Used in Agriculture?

If you concentrate on the phosphoric acid used in agriculture, you will understand that phosphate is the prime constituent of fertilizers. In fact, it also acts as a pH buffer for the soil and can protect the plants.

3. Is Phosphoric Acid Hazardous?

This acid is not as hazardous as the strong mineral acids but its fumes can cause irritation in the sense organs.