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.
Conclusion
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. What is the main role of phosphoric acid in foods and soft drinks?
In the food and beverage industry, phosphoric acid is primarily used as an acidity regulator. It gives a distinct tangy flavour to many soft drinks, especially colas, and helps to slow the growth of mould and bacteria, which extends the shelf life of processed foods.
2. How does phosphoric acid contribute to agriculture?
Phosphoric acid is a vital source of phosphorus, an essential nutrient for plant growth. It is a key ingredient in the production of phosphate fertilisers. Additionally, it can be used to lower the pH of alkaline soils, making essential nutrients more available to plants.
3. Why is phosphoric acid classified as a tribasic acid?
Phosphoric acid (H₃PO₄) is known as a tribasic acid because one molecule has three acidic hydrogen atoms that it can donate. When reacting with a base, it can release these three hydrogen ions in steps, allowing it to form three different types of salts.
4. How does phosphoric acid work as a rust remover?
Phosphoric acid is effective at removing rust because it chemically reacts with iron oxide (the rust). This reaction converts the rust into ferric phosphate, a water-soluble compound that can be easily washed away. This process also creates a protective phosphate coating that helps prevent future rusting, a technique known as passivation.
5. What is the significance of the common 85% concentration of phosphoric acid?
The 85% concentration is a standard commercial grade because it offers a good balance of potency and safety. In this form, it is a stable, non-volatile syrupy liquid that is easier and safer to transport and handle than more concentrated or fuming forms of the acid, while still being effective for most industrial applications.
6. Besides food and fertiliser, what are some other important uses of phosphoric acid?
Phosphoric acid has several other key industrial applications, including:
- Dentistry: Used as an etching solution to clean and roughen the surface of teeth before fillings are applied.
- Metal Treatment: Applied to steel surfaces to improve paint adhesion and provide corrosion resistance.
- Water Treatment: Helps to prevent the formation of scale and corrosion in water pipes.
- Catalysis: Acts as a chemical catalyst in the production of substances like ethanol.
7. What makes phosphoric acid important for the human body?
Phosphates derived from phosphoric acid are fundamental to life. They are a crucial building block of DNA, RNA, and ATP (the molecule that carries energy in our cells). Furthermore, our bones and teeth are primarily made of calcium phosphate, a salt of phosphoric acid, which gives them their strength and structure.
8. Is phosphoric acid considered a dangerous chemical?
While it's a weaker acid compared to sulfuric or hydrochloric acid, phosphoric acid is still hazardous and must be handled with care. Concentrated solutions can cause serious skin burns, eye damage, and respiratory irritation if the fumes are inhaled. Using protective gear like gloves and goggles is essential.
