Phosphoric Acid

Last Updated: April 28, 2024

Phosphoric Acid

Phosphoric acid is a key player in the world of chemistry. It is a substance you might not see, but it plays a huge role in things we use regularly. This acid known scientifically as H₃PO₄. It is not just any acid. It’s a superhero in the chemistry lab, making its mark in everything from fertilizers that help our food grow to the soft drinks we enjoy. It’s a clear, colorless liquid with a slightly syrupy consistency that can also appear in a solid form as crystals at lower temperatures. Phosphoric acid is fascinating because it shows us how it is part of our daily lives, from the food we eat to the products we use.

What is Phosphoric Acid?

Phosphoric Acid is a commonly used chemical substance. It is recognized for its role in the creation of fertilizers and various food products. This clear, odorless liquid, scientifically termed as H₃PO₄ , is not only crucial in agriculture but also finds its place in household cleaning agents and even in some soft drinks for that tangy taste. Its versatility extends to the industrial sector, where it’s used in metal treatment and as a component in making certain plastics and synthetic materials. Despite its widespread use, handling Phosphoric Acid requires care due to its acidic nature, which can cause irritation upon direct contact.

Chemical Names and Formulas

Hill FormulaH₃O₄P
NamePhosphoric acid
Alternate NamesOrthophosphoric acid, Evits, Sonac, White phosphoric acid

Structure of Phosphoric Acid


Phosphoric Acid, known to scientists as H₃PO₄, has a fascinating structure that makes it quite unique. Picture a central phosphorus atom, like the sun in our solar system, surrounded by four oxygen atoms, similar to planets. Three of these oxygen atoms hold onto a hydrogen atom each, like moons orbiting their planets. This special arrangement gives Phosphoric Acid its acidic properties, allowing it to participate in various chemical reactions, from fertilizing plants to flavoring your favorite soft drinks. Its structure not only explains why it’s an acid but also how it can form strong bonds with other substances, making it incredibly useful in both nature and industry.

Preparation of Phosphoric Acid

Preparing Phosphoric Acid, a key ingredient in many everyday products, involves a chemical process that starts with a mineral called phosphorus rock. The most common method is called the wet process. Here’s how it works: the phosphorus rock is mixed with sulfuric acid, leading to a chemical reaction that produces Phosphoric Acid. The equation for this reaction looks something like this:

5Ca₅(PO₄)₃F + 5H₂SO₄ + 10H₂O → 5CaSO₄·2H₂O + 3H₃PO₄ + HF

This equation shows how calcium phosphate (from the rock), sulfuric acid, and water mix together to create Phosphoric Acid, gypsum (a by-product), and hydrogen fluoride. The Phosphoric Acid produced through this process is not only crucial for making fertilizers but also plays a significant role in food and beverage industries, adding that tangy taste to some of your favorite drinks.

Physical Properties of Phosphoric Acid

AppearanceClear, colorless syrupy liquid or a solid (when pure)
Chemical FormulaH3PO4
Melting Point42.35°C (solid form)
Boiling Point158°C (decomposes)
Density1.885 g/cm³ (at 85% concentration)
SolubilityCompletely soluble in water, forming a mildly acidic solution
pHHighly acidic, with a pH of around 2 in its common concentrations

Chemical properties of Phosphoric Acid

Acidic Nature

  • Phosphoric Acid is a triprotic acid, meaning it can donate three hydrogen ions (H⁺) in reactions. This property makes it an effective acid for adjusting the acidity in food and beverages.
  • Equation: H₃PO₄ → H⁺ + H₂PO₄⁻

Reaction with Bases

  • It reacts with bases to form phosphate salts. For example, when it reacts with sodium hydroxide (NaOH), sodium phosphate (Na₃PO₄) and water are produced.
  • Equation: H₃PO₄ + 3NaOH → Na₃PO₄ + 3H₂O

Formation of Ester

  • Phosphoric Acid can react with alcohols to form esters, a process widely used in organic chemistry and manufacturing of various products.
  • Equation: H₃PO₄ + ROH → ROP(OH)₂ + H₂O where R is an alkyl group

Dehydration Ability

  • Phosphoric Acid can act as a dehydrating agent, removing water from compounds. This property is used in organic synthesis, such as concentrating nitric acid by removing water. ​
  • Equation: HNO₃ + H₃PO₄ → H₂O + NO₂ + H₂PO₄⁻

Corrosion Resistance

  • When applied to metals, Phosphoric Acid forms a protective layer that can prevent rust and corrosion. This makes it useful in metal cleaning and protection processes.

Phosphoric Acid (H₃PO₄ ) Chemical Compound Information

Chemical Identifiers

CAS registry number7664-38-2
Beilstein number1921286
PubChem compound ID1004
PubChem substance ID24861303
SMILES identifierOP(=O)(O)O
InChI identifierInChI=1/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/f/h1-3H
RTECS numberTB6300000
MDL numberMFCD00011340

NFPA Label

NFPA health rating2
NFPA fire rating0
NFPA reactivity rating0

Uses of Phosphoric Acid


Fertilizer Production

Phosphoric Acid is a key ingredient in manufacturing fertilizers, especially those that supply phosphate, a crucial nutrient for plant growth. It helps to promote root development and increase crop yields.

Food and Beverage Industry

In the food industry, Phosphoric Acid is used as a food additive to acidify foods and beverages like colas, providing a tangy or sour taste. It also serves as a preservative to prolong the shelf life of various products.

Cleaning Products

Due to its ability to dissolve rust and mineral deposits, Phosphoric Acid is commonly found in household cleaning products. It’s particularly effective in toilet bowl cleaners and products designed to clean hard water stains.

Metal Treatment

In metalworking, Phosphoric Acid is used to prepare metal surfaces for coating or painting. It helps to create a protective layer that prevents rust and improves paint adhesion.

Dental and Medical Applications

Phosphoric Acid is also used in dentistry as an etching solution to clean and roughen the surfaces of teeth before filling them. Additionally, it’s employed in various medical syrups to adjust pH levels.

Water Treatment

This acid plays a role in water treatment facilities, where it is used to remove impurities and contaminants from water, making it safe for drinking.

Pharmaceutical Industry

In pharmaceutical manufacturing, Phosphoric Acid is utilized as a reagent and pH adjuster in various medications, ensuring they are effective and safe for consumption.

Side Effects of Phosphoric Acid

  • Skin and Eye Irritation: Direct contact with Phosphoric Acid can cause severe irritation to the skin and eyes. It can lead to burns or even temporary blindness if the eyes are exposed.
  • Digestive Issues: Consuming large amounts of Phosphoric Acid, such as from excessive intake of beverages containing this acid, can lead to digestive discomfort. Symptoms may include stomach ache, nausea, and diarrhea.
  • Bone Density Reduction: Long-term consumption of high levels of Phosphoric Acid, particularly through soft drinks, has been linked to lower bone density. This condition can increase the risk of osteoporosis, which weakens bones and makes them more susceptible to fractures.
  • Dental Erosion: Phosphoric Acid in soft drinks and other acidic beverages can erode tooth enamel over time. This dental erosion not only makes teeth more sensitive but also more prone to decay.
  • Nutrient Absorption Issues: Phosphoric Acid can interfere with the body’s ability to absorb iron and calcium, essential nutrients for maintaining healthy blood and bones. This can lead to deficiencies if not monitored.


Is Phosphoric Acid Harmful to the Body?

Phosphoric Acid can be harmful, causing digestive issues and reducing bone density if consumed excessively.

Is Phosphoric Acid Strong or Weak?

Phosphoric Acid is a moderately strong acid, capable of donating three hydrogen ions in aqueous solutions.

What Happens If You Drink Phosphoric Acid?

Drinking Phosphoric Acid in high concentrations can cause severe irritation to the gastrointestinal tract, leading to pain and nausea.

How Much Phosphoric Acid is Lethal?

The lethal dose of Phosphoric Acid varies, but ingestion of highly concentrated forms can be fatal due to chemical burns and organ damage.

AI Generator

Text prompt

Add Tone

10 Examples of Public speaking

20 Examples of Gas lighting