Phosphoric acid (H3PO4) is a colorless, odorless mineral acid. It is widely used in the food and beverage industry as a flavoring agent and as a rust inhibitor in the automotive industry.
| IUPAC Name | Phosphoric acid |
| Molecular Formula | H3PO4 |
| CAS Number | 7664-38-2 |
| Synonyms | Orthophosphoric acid, trihydroxidooxidophosphorus, phosphoric(V) acid, orthophosphoric acid, phosphoric acid clear tech, phosphorsaeure |
| InChI | InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4) |
Phosphoric acid Properties
Phosphoric acid molar mass
The molar mass of phosphoric acid is 98.00 g/mol. This value is calculated by adding the atomic masses of each of the constituent atoms in the molecule, which are one phosphorus atom and three oxygen atoms. The molar mass is an important property of a compound, as it is used to calculate the amount of substance present in a given sample using the Avogadro’s number. In addition, the molar mass of phosphoric acid is used to determine the concentration of a solution through titration.
Phosphoric acid formula
The chemical formula for phosphoric acid is H3PO4, which indicates that it contains one phosphorus atom, three hydrogen atoms, and four oxygen atoms. It is a weak acid that can donate up to three hydrogen ions to a base. The formula is important because it allows us to write chemical equations and calculate the stoichiometry of chemical reactions involving phosphoric acid. In addition, the formula is used to calculate the concentration of a solution of phosphoric acid through titration.
Phosphoric acid boiling point
The boiling point of phosphoric acid is 158°C (316°F) at 1 atm pressure. This means that at this temperature and pressure, the liquid phase of phosphoric acid will convert to a gaseous phase. The boiling point is dependent on the intermolecular forces present in the compound, and in the case of phosphoric acid, it is due to the presence of hydrogen bonds between the molecules. Boiling point is an important physical property of a compound, as it is used to determine its volatility, which is useful in many industrial processes.
Phosphoric acid melting point
The melting point of phosphoric acid is 42.35°C (108.23°F). This is the temperature at which the solid phase of phosphoric acid will convert to a liquid phase. The melting point is dependent on the strength of the intermolecular forces present in the compound, and in the case of phosphoric acid, it is due to the presence of hydrogen bonds between the molecules. Melting point is an important physical property of a compound, as it is used to determine its purity and to establish its identity.
Phosphoric acid density g/ml
The density of phosphoric acid is 1.685 g/ml at room temperature (25°C or 77°F). This is the mass of the substance per unit volume. The density is a physical property of a substance and it is used to calculate the volume of a given mass of the substance or the mass of a given volume of the substance. The density of phosphoric acid is important in many industrial processes, including the production of fertilizers, detergents, and food additives.
Phosphoric acid molecular weight
The molecular weight of phosphoric acid is 98.00 g/mol. This is the sum of the atomic weights of all the atoms in the molecule. The molecular weight is an important property of a compound, as it is used to calculate the amount of substance present in a given sample. In addition, the molecular weight of phosphoric acid is used to determine the concentration of a solution through titration.
Phosphoric acid (H3PO4) structure
Phosphoric acid has a molecular formula of H3PO4 and a tetrahedral molecular geometry. It is a triprotic acid, meaning that it can donate three hydrogen ions to a base. The molecule contains one phosphorus atom bonded to four oxygen atoms, three of which are bonded to hydrogen atoms. The structure of phosphoric acid is important because it determines its chemical and physical properties. The presence of hydrogen bonds between the molecules gives rise to its high boiling and melting points.
| Appearance | Colorless liquid |
| Specific Gravity | 1.685 at 25°C |
| Color | Colorless |
| Odor | Odorless |
| Molar Mass | 98.00 g/mol |
| Density | 1.685 g/ml at 25°C |
| Melting Point | 42.35°C (108.23°F) |
| Boiling Point | 158°C (316°F) at 1 atm pressure |
| Flash Point | Not applicable |
| Water Solubility | Completely soluble in water |
| Solubility | Soluble in ethanol, diethyl ether and acetone |
| Vapour Pressure | 0.0002 mmHg at 20°C |
| Vapour Density | 3.5 (air = 1) |
| pKa | pKa1=2.148, pKa2=7.198, pKa3=12.319 |
| pH | 1.0 – 2.5 (concentrated solution), 2.8 – 3.2 (dilute solution) |
H3PO4 Safety and Hazards
Phosphoric acid poses several safety hazards and should be handled with care. It can cause severe skin and eye irritation and is highly corrosive to metals. Direct contact with the skin, eyes or mucous membranes can cause severe burns and even permanent damage. Inhalation of the fumes can cause respiratory irritation and burns. It should not be ingested as it can cause severe internal burns and gastrointestinal disturbances. When handling phosphoric acid, appropriate personal protective equipment such as gloves, goggles, and a respirator should be worn. It should also be stored in a cool, dry place away from incompatible materials such as oxidizing agents and alkalis.
| Hazard Symbols | Corrosive |
| Safety Description | Keep container tightly closed. Wear protective gloves/protective clothing/eye protection/face protection. |
| UN IDs | UN1805 |
| HS Code | 280920 |
| Hazard Class | 8 (Corrosive substances) |
| Packing Group | II (medium danger) |
| Toxicity | Oral LD50 (rat) – 1533 mg/kg |
H3PO4 Synthesis Methods
Several methods exist for synthesizing phosphoric acid (H3PO4).
The most common method is the wet process which involves the reaction of phosphate rock with sulfuric acid. To produce calcium sulfate (gypsum) and H3PO4, phosphate rock is first ground and then mixed with concentrated sulfuric acid. After filtering the resulting slurry, the series of solvent extraction and precipitation steps purify the H3PO4.
Another method for the synthesis of H3PO4 is the thermal process which involves heating phosphate rock to a high temperature to produce H3PO4 and other by-products such as elemental phosphorus and calcium oxide. This method is less common than the wet process due to its high energy requirements.
The reaction of phosphorus pentoxide with water synthesizes H3PO4. The electronics and semiconductor industries commonly use this method for producing high-purity H3PO4.
Other methods for the synthesis of H3PO4 include the electrochemical oxidation of phosphorus, the hydrolysis of phosphorus trichloride, and the reaction of phosphorus with nitric acid. These methods are less common than wet and thermal processes due to their high cost and complexity.
H3PO4 Uses
Phosphoric acid is a versatile compound that has a wide range of applications across various industries. Some of its major uses are:
- Fertilizer production: Primary component in the production of fertilizers such as diammonium phosphate and triple superphosphate.
- Food and beverage industry: Used as a food additive and flavoring agent in various food and beverage products such as cola drinks, jams, and processed cheese.
- Industrial cleaning: Used as a cleaner and rust remover in the industrial sector due to its ability to dissolve rust and other mineral deposits.
- Water treatment: Used to control the pH levels of water in industrial processes and also to remove heavy metals and other impurities.
- Pharmaceuticals: Used in the production of pharmaceuticals and dietary supplements due to its ability to regulate pH levels.
- Dentistry: Used in dental procedures such as root canal treatment and as a component in dental cement.
- Metal treatment: Used to treat and passivate metals such as stainless steel, aluminum, and titanium to improve their corrosion resistance.
- Electronics: Used in the electronics industry as a cleaning agent and as a component in the production of semiconductors.
Questions:
Q: What is the formula for phosphoric acid?
A: The formula for phosphoric acid is H3PO4.
Q: Is H3PO4 a strong acid?
A: No, H3PO4 is not considered a strong acid. It is a weak acid with a pKa value of 2.15.
Q: Is H3PO4 an acid or base?
A: H3PO4 is an acid because it donates a proton (H+) when dissolved in water.
Q: What is the Lewis structure for H3PO4?
A: The Lewis structure for H3PO4 is a tetrahedral structure with one central phosphorus atom surrounded by four oxygen atoms. Each oxygen atom forms a single bond with the phosphorus atom, and there are also three lone pairs of electrons on each oxygen atom.
Q: Is phosphoric acid a strong acid? A: No, phosphoric acid is not considered a strong acid. It is a weak acid with a pKa value of 2.15 for the first proton donation and 7.20 for the second proton donation.