Phosphoric Acid

Bookmark added to your notes.
View Notes
×

Phosphoric acid is one of the foremost popular acids that are utilized in many industries, especially within the manufacturing of fertilizers. The salts of this acid which are referred to as phosphates are used mainly in agriculture and even reception. Students might even hear this term often in their chemistry classes. Therefore, we will learn about this chemical compound and understand various things related to it here on this page.

Phosphoric acid belongs in the category of weak acids. It is also mentioned as phosphoric acid which helps us to simply distinguish it from other phosphoric acids like oxyacid. Another name for this acid is phosphoric(V) acid. Phosphoric acid’s formula is written as H3PO4. This acid is a non-toxic acid and in its pure form, it is a solid at room temperature. It has a molar mass of 97.99 g/mol.

H3PO4 is one of the foremost important and useful mineral acids. The acid is mostly available in the form of an aqueous solution (almost 85%) and is odorless, colorless, and non-volatile liquid. The answer is a sticky liquid and even though this acid is categorized as a weak acid it can still cause irritation or burns in the skin as well as damage to the eyes and membranes in the nose.

IUPAC Name

Ortho Phosphoric Acid

Chemical Formula

H3PO4

Molar Mass

97.99 g/mol

Density

2.030 g.cm-3

Melting Point

42.4 °C (108.3 °F; 315.5 K)

Boiling Point

407 °C (765 °F; 680 K)


Phosphoric Acid Structure

When we talk about the structure of phosphoric acid, the central phosphorus atom is bonded together with an oxygen atom through a double bond. It is also connected to 3 hydroxyls (-OH) groups through single bonds.

[Image to be added soon]

Phosphoric Acid Properties

Below we will look at the chemical and physical properties of H3PO4.

Physical Properties

  • Pure phosphoric acid is normally in the form of a white crystalline solid.

  • It has a melting point of 42.4° C.

  • The acid is colorless.

  • It is also odorless and a viscous liquid with a density of 2.030 g.cm-3.

  • H3PO4 is non-toxic and non-volatile.

Chemical Properties

  • Phosphoric acid or H3PO4 can release up to 3 H+ ions. Due to this property, it can react differently in comparison to other mineral acids.

  • Reaction with bases usually results in the formation of three classes of salts.

  • When the molecules of orthophosphoric acid are exposed to high temperatures it forms dimers, trimers, and even long polymeric chains as seen in polyphosphoric acids and meta-phosphoric acids.

Preparation Of Phosphoric Acid

Phosphoric acid is typically prepared or manufactured using two different processes. These include:

a) The ‘wet’ process.

b) Thermal process.

We will look at the process in detail below:

(a) Wet Process

During the wet process, orthophosphoric acid is produced from a present crystal rock referred to as fluorapatite which contains the phosphate mineral. This compound is reacted with concentrated sulfuric acid and water. When the reaction takes place it leads to the formation of orthophosphoric acid and calcium sulfate (gypsum) also as some insoluble impurities. The extra chemical compounds and impurities are removed by the process of filtration and evaporation. The product from the ‘wet process’ acid is impure but is often used, without further purification, for fertilizer manufacture.

(b) Thermal Process

Another method that is used in obtaining phosphoric acid is the thermal process. In this, phosphorus is heated or burnt at high temperature in the presence of air. The burning leads to the generation of phosphorus pentoxide which is then condensed to make a white powder. It is then hydrated in a separate process to obtain phosphoric acid.

Sometimes steam is additionally added within the burner where a condensed sort of polyphosphoric acid is produced. The products are then directly passed into a hydration tower where the gaseous phosphorus oxide is absorbed and orthophosphoric acid is obtained. Nonetheless, a purer product is obtained in the first process.

Phosphoric Acid Uses

Phosphoric acid is one of the foremost popular chemical compounds that have several uses in several industries and even in products that we consume. Here are some popular uses of H3PO4.

In Agriculture

One of the foremost common uses of orthophosphoric acid is within the agriculture domain. It is widely used in the production of fertilizer and as a flavoring agent in animal or poultry feed.

In Dentistry

It is also used in dentistry where dentists often use the chemical compound as an etching solution and for cleaning the teeth. Phosphoric acid is additionally found in mouth cleaning products. Alternatively, phosphoric acid is found in anti-nausea medicines.

Treatment of Rust

Phosphoric acid is additionally utilized in treating rusts and removing them from metal components. It is used in the process of the phosphate conversion coating. This helps in corrosion resistance.

Skincare Products

Phosphoric acid mostly utilized in adjusting or controlling the pH level in skincare products. It is used in toothpaste, soaps, and detergents as well.

In The Food And Beverage Industry

Phosphoric acid is often used as a food additive and is mainly utilized to acidify foods and beverages. It helps in creating a certain taste.

Other Applications

  • It is used in phosphoric acid fuel cells.

  • Production of activated carbon.

  • Compound semiconductor processing.

  • It is used in sanitizing brewing and dairy industries.

Phosphates

Phosphates are basically the salts of phosphates. Here we will look at three important phosphates of H3PO4.

(a) Ammonium Phosphates

Some of the common phosphate salts include monoammonium dihydrogen phosphate and diammonium hydrogen phosphate. These are prepared by combining anhydrous ammonia with orthophosphoric acid. They are mostly used as fertilizers.

(b) Calcium Phosphates

We have already talked about these above in the preparation of phosphoric acid. This type of phosphate is also called superphosphate.

(c) Sodium Phosphates

When phosphoric acid is reacted with a concentrated solution of sodium hydroxide under controlled conditions and proportions sodium phosphates are formed. The product that is generated is in the form of solid crystals. Some of the examples of sodium phosphates are Monosodium dihydrogen phosphate, Disodium hydrogen phosphate, Trisodium phosphate, Disodium pyrophosphate.

Phosphoric Acid Hazards

Phosphoric acid is non-toxic and does not have any harm to the skin or any part of the body in low concentration. It is dangerous only at higher concentrations and can cause severe skin irritation or burns and even damage to the eyes. H3PO4 can also cause irritation in the respiratory tract if vapors are inhaled. This acid should be stored in a metallic or coated fiberboard container (with polyethylene inner package) and kept in a cool and well-ventilated place.

FAQ (Frequently Asked Questions)

Q1. Define Phosphoric Acid.

Ans - Phosphoric acid is one among the foremost popular acids that's utilized in many industries, especially within the manufacturing of fertilizers. The salts of this acid which are referred to as phosphates are used mainly in agriculture and even reception . Students might even hear this term often in their chemistry classes. Therefore, we will learn about this chemical compound and understand various things related to it here on this page.

Q2. What are the Physical Properties of Phosphoric Acid?

Ans - Physical properties of Phosphoric Acid are - 

  • Pure phosphoric acid is normally in the form of a white crystalline solid.

  • It has a melting point of 42.4° C.

  • The acid is colorless.

  • It is also odorless and a viscous liquid with a density of 2.030 g.cm-3.

  • H3PO4 is non-toxic and non-volatile.