How is phosphoric acid made and its properties

To know how is phosphoric acid made you should know what it is and what it does. Phosphoric acid is a strong acid that is used to create fertilizers and a wide range of synthetic materials. The manufacturing process for phosphoric acid begins with limestone or calcium oxide, which is then treated with sulphuric acid and phosphorus pentasulfide to create the required sulphur dioxide gas. The gas reacts with the water in the milky substance called white caustic soda to produce phosphoric acid as well as hydrogen phosphate, calcium hydroxylapatite, hydrogen sulfate, ammonium hydrosulphide and ammonium sulfate.

Properties of phosphoric acid

1.Phosphoric acid is a deliquescent solid

This means that the acid dissolves in water, forming a mixture of salt and water. It is more than 98% soluble in water. To make it less soluble, add a little magnesium silicate. It may also be used directly in its salt form (phosphoric acid is not hygroscopic).

2. The pH of phosphoric acid is 1.5 at 15 degrees Celsius (in solution)

This means that the solution will be acidic. For example, if you mix phosphoric acid with a hydroxide like sodium hydroxide, you get sodium phosphate or with calcium hydroxide you get calcium phosphate.

3. Phosphoric acid is a strong acid

This means that it produces a lot of hydronium ions when it is mixed with water. For example, if you mix concentrated phosphoric acid with water, you get hydrogen phosphate and the solution will be acidic. The same thing happens when you mix sulfuric acid and water; the solution is acidic and its pH is 1 at 25 degrees Celsius.

4.Phosphoric acid can dimerize via a dehydration reaction to form phospho anhydrides

Theoretical studies have shown that phosphoric acid can exist in three different forms: as the endo , exo and anhydride forms. The anhydride form is the most stable of the three, but when you add water to it, the reaction is more favorable for formation of the exo form. It is formed by heating phosphoric acid with concentrated NaOH.

5.Boiling Point: 158 ℃

The boiling point of phosphoric acid is 158℃. The gas, PH3, can be made by removing oxygen from the mixture using zinc oxide with a little sulfuric acid.

6.Density: 1.66g/cm³

The density of the liquid is much greater than that of water. Phosphoric acid has a density in the range 1-1.6 g/cm³, which is much more than that of water at 1 g/cm . The density increases considerably when the liquid reacts with water to form a salt (phosphate) having a density between 1 and 1.

7.Molecular Weight/ Molar Mass: 97.994 g/mol

The molecular weight is found by subtracting the weights of the atoms from that of the molecule. The weight is calculated using the molar mass, which for phosphoric acid is 97.994 g/mol .

8. Molecular Formula: H₃PO₄

The molecule contains a central phosphorus atom with an oxidation state of +5. It is surrounded by four atoms of hydrogen and three atoms of oxygen in a tetrahedral arrangement giving H₃PO₄ as its molecular formula. The bond angles are 108 degrees which form linear molecules in solids and liquids and frustro-linear molecules in gas states at normal temperature and pressure conditions.

Uses of phosphoric acid made

1.Sulphuric Acid

Sulphuric acid is produced from phosphoric acid by passing water through a column containing calcium oxide. The reaction is then terminated with concentrated H₂SO₄. The gas (a mixture of H₃PO₄ and SO₄) is scrubbed on a filter press, producing the syrup known as "white caustic soda" which is a mixture of sodium and potassium hydroxide, sodium hydrogen carbonate and other impurities. When the solids are washed in an evaporator they yield dry white salt that may be used either as an agricultural fertilizer or in the manufacture of other chemicals. This also shows how is phosphoric acid made.

2.Phosphates

Phosphoric acid is used to produce the phosphates that are important agricultural fertilizers: sodium, potassium and calcium phosphates. For example, in North America most calcareous soils are acidic (the pH is less than 7.0) and the calcium phosphate fertilizers make up a large part of the fertilizer applied to such soils. The increasingly acid soils in various parts of the world have led to an increased demand for calcium phosphate fertilizers from farmers and forest owners. The discovery of huge deposits of sodium phosphate in Chile has also made it possible to meet this demand by importing sodium phosphates instead of natural sources of these minerals.

In conclusion, how is phosphoric acid made is a process of converting natural materials into a synthetic product such as fertilizers. It starts with turning limestone or calcium oxide into phosphoric acid. This is done by reacting it with sulphuric acid and phosphorus pentasulfide.