The term ‘phosphate’ refers to an anion, salt, functional group or the numerous compounds derived from phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\). A phosphate ion is an inorganic polyatomic ion with the chemical formula \({\rm{PO}}_{\rm{4}}^{{\rm{3 – }}}.\) It is also known as orthophosphate ion. In this article, we are going to discuss phosphate formula, Phosphate ions, hydrogen phosphate ions and some compounds related to them.

Phosphate Ion (PO₄^3-)

A phosphate ion is formed when three protons are removed from phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\). It is a polyatomic ion with the formula \(\mathrm{PO}_{4}{ }^{3-}\). It is also called a phosphate group. In this ion, the central phosphorous ion is surrounded by four oxygen atoms. Hence, it has a tetrahedral shape. It can be shown as,

The molar mass of phosphate ions is \(94.97 \mathrm{~g} / \mathrm{mol}\)

Occurrence of Phosphate Ion

The phosphate ion can be found naturally in human bodies (as sodium and potassium phosphates), water and in some foods. It is found in rocks and minerals (as iron phosphate, cobalt phosphate, aluminium phosphate, etc.). Another important occurrence of phosphates in our human body is that they form the structural material for bone and teeth.

Hydrogen Phosphate Formula

Hydrogen phosphate is an inorganic ion with the chemical formula \(\left[\mathrm{HPO}_{4}\right]^{2-}\). It is also called monohydrogen phosphate. The hydrogen phosphate ion is formed when the phosphoric acid loses two protons from it. Let us discuss more about hydrogen phosphate anion.

Hydrogen Phosphate Ion [HPO₄]^2-

Hydrogen phosphate, \([\left.\mathrm{HPO}_{4}\right]^{2 \text { – }}\) ion is formed when the phosphoric acid loses two protons from it. In hydrogen phosphate ion, the central atom is the phosphorous atom, which is surrounded by three oxygen atoms in which one oxygen has hydrogen attached (forming a hydroxyl group). Hydrogen phosphate ion can be represented as,

The molar mass of hydrogen phosphate ion is \(95.979 \mathrm{~g} / \mathrm{mol}\).

Hydrogen phosphate ion occurs naturally in biological systems. Common compounds containing hydrogen phosphate ion includes lithium hydrogen phosphate, sodium hydrogen phosphate, potassium hydrogen phosphate, etc.

As the term phosphate also relates to numerous chemical compounds formed from phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\), we will discuss some of them in detail.

Magnesium Phosphate Formula

Magnesium phosphate is an inorganic compound with the chemical formula \(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\). It is also known as trimagnesium phosphate. It is the magnesium salt of phosphoric acid. Let us discuss more about magnesium phosphate.

Magnesium Phosphate [Mg₃(PO₄)₂]

Magnesium phosphate, \(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) contains three magnesium \(\left(\mathrm{Mg}^{2+}\right)\) ions and two phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) ions. It is an ionic compound. Magnesium phosphate can be represented as,

The molar mass of magnesium phosphate is \(262.85 \mathrm{~g} / \mathrm{mol}\).

Preparation of Magnesium Phosphate [Mg₃(PO₄)₂]

Magnesium phosphate can be prepared by the action of phosphoric acid with magnesium metal or magnesium hydroxide, or magnesium chloride. For example, magnesium reacts with phosphoric acid to produce magnesium phosphate. That is,

\(\mathrm{Mg}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right){2}+\mathrm{H}_{2}\)

Similarly, magnesium chloride reacts with phosphoric acid to give magnesium phosphate. That is,

\(\mathrm{MgCl}_{2}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}+\mathrm{HCl}\)

Magnesium hydroxide also reacts with phosphoric acid to give magnesium phosphate. That is,

\(\mathrm{H}_{3} \mathrm{PO}_{4}+\mathrm{Mg}(\mathrm{OH})_{2} \rightarrow \mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}+\mathrm{H}_{2} \mathrm{O}\)

Let us discuss the physical and chemical properties of magnesium phosphate \(\left[\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\right]\).

Physical Properties of Magnesium Phosphate [Mg₃(PO₄)₂]

Magnesium phosphate is white in colour. It appears as a powder. It is insoluble in water and soluble in salt solutions.

Chemical Properties of Magnesium Phosphate [Mg₃(PO₄)₂]

1. Magnesium phosphate \(\left[\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\right]\) reacts with water to form phosphoric acid and magnesium hydroxide. That is,

\(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right){2}+6 \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{H}_{3} \mathrm{PO}_{4}+3 \mathrm{Mg}(\mathrm{OH})_{2}\)

2. Magnesium phosphate \(\left[\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\right]\) reacts with hydrochloric acid to form magnesium chloride and phosphoric acid. That is,

\(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}+6 \mathrm{HCl} \rightarrow 3 \mathrm{MgCl}_{2}+2 \mathrm{H}_{3} \mathrm{PO}_{4}\)

Uses of Magnesium Phosphate [Mg₃(PO₄)₂]

1. It is most commonly used as an antacid.
2. It is used as a fertilizer for crops.
3. It is used for the treatment of vitamin \(\text {E}\) deficiency.
4. It is used in some foods in controlled amounts.
5. It is used as a soil conditioner.

Ammonium Phosphate Formula

Ammonium phosphate is an inorganic compound. Its chemical formula is \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\). It is an ammonium salt of phosphoric acid. Let us discuss more about ammonium phosphate.

Ammonium Phosphate [(NH₄)₃PO₄]

The chemical formula of ammonium phosphate is \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\). It is salt. In this compound, ammonium \(\left(\mathrm{NH}_{4}^{+}\right)\) cations and phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) anions are present. Ammonium phosphate can be represented as,

The molar mass of ammonium phosphate is \(149.09 \mathrm{~g} / \mathrm{mol}\).

Preparation of Ammonium Phosphate

Ammonium phosphate can be prepared by the reaction of concentrated phosphoric acid \(\left( {85\% } \right)\) with a \(30\% \) ammonia solution. The chemical equation for the reaction can be given as,

\(\mathrm{H}_{3} \mathrm{PO}_{4}+3 \mathrm{NH}_{3} \rightarrow\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\)

Properties of Ammonium Phosphate

Let us discuss the physical and chemical properties of ammonium phosphate. 

Physical Properties of Ammonium Phosphate

Ammonium phosphate is a colourless crystalline solid. It is readily soluble in water. Ammonium phosphate is a highly unstable compound, and hence, it does not have a large commercial value. 

Chemical Properties of Ammonium Phosphate

1. Decomposition of Ammonium Phosphate

Ammonium phosphate decomposes, emitting toxic fumes. This results in the formation of ammonia and phosphoric acid. That is,

\(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} \rightarrow \mathrm{H}_{3} \mathrm{PO}_{4}+3 \mathrm{NH}_{3}\)

2. Reaction of Ammonium Phosphate with Lead (IV) Nitrate

Ammonium phosphate reacts with lead (IV) nitrate to form lead phosphate and ammonium nitrate. That is,

\(4\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}+3 \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{4} \rightarrow \mathrm{Pb}_{3}\left(\mathrm{PO}_{4}\right)_{4}+12 \mathrm{NH}_{4} \mathrm{NO}_{3}\)

Uses of Ammonium Phosphate

Ammonium phosphate, due to its unstable nature, does not have a large commercial value. However, it has got some uses. They are:

1. Ammonium phosphate is majorly used in fertilizers.
2. Ammonium phosphate is used as a flame retardant in some thermoplastic compositions.
3. Ammonium phosphate is used as a leavening agent in baking.

Calcium Superphosphate Formula

Calcium superphosphate is an inorganic compound. Its chemical formula is \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}\). It is also known as monocalcium phosphate, calcium acid phosphate, calcium biphosphate, calcium diorthophosphate, monocalcium orthophosphate or monobasic calcium phosphate. Let us discuss more about calcium superphosphate. Calcium superphosphate is commonly found in the monohydrate form, \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \cdot \mathrm{H}_{2} \mathrm{O}\).

Calcium Superphosphate [Ca(H₂PO₄)₂]

The chemical formula of calcium superphosphate is \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}\). Calcium superphosphate can be represented as,

The molar mass of calcium superphosphate is \(234.05 \mathrm{~g} / \mathrm{mol}\).

Preparation of Calcium Superphosphate

Calcium superphosphate can be prepared by treating calcium hydroxide with phosphoric acid. That is,

\(\mathrm{Ca}(\mathrm{OH})_{2}+2 \mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}+2 \mathrm{H}_{2} \mathrm{O}\)

The \(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2}\) thus formed tend to form dicalcium phosphate. That is,

\(\mathrm{Ca}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)_{2} \rightarrow \mathrm{Ca}\left(\mathrm{HPO}_{4}\right)+\mathrm{H}_{3} \mathrm{PO}_{4}\)

Properties of Calcium Superphosphate

Calcium superphosphate appears as a white powder. It is sparingly soluble in water and insoluble in ethanol.

Uses of Calcium Superphosphate

1. Calcium superphosphate is majorly used in fertilizers.
2. It is used in the food industry as a leavening agent as it helps the baked food to rise.

Ferric Phosphate Formula

Ferric phosphate is an inorganic compound. Its chemical formula is \(\mathrm{FePO}_{4}\). It is also known as ferric orthophosphate or iron(III) phosphate. Let us discuss more about ferric phosphate.

Ferric Phosphate [FePO₄]

Ferric phosphate, \(\mathrm{FePO}_{4}\) contains \(\mathrm{Fe}^{3+}\) ions and \(\mathrm{PO}_{4}^{3-}\) ions. Ferric phosphate can be represented as,

The molar mass of ferric phosphate is \(150.815 \mathrm{~g} / \mathrm{mol}\).

Preparation of Ferric Phosphate

Ferric phosphate can be prepared by the reaction of sodium phosphate with ferric chloride \(\left(\mathrm{FeCl}_{3}\right)\). That is,

\(\mathrm{FeCl}_{3}+\mathrm{Na}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{FePO}_{4}+3 \mathrm{NaCl}\)

It can also be prepared by the action of sodium phosphate with ferric citrate.

Properties of Ferric Phosphate

Ferric phosphate appears as a yellow-brown solid. It is insoluble in water but soluble in acids. In ferric phosphate, the oxidation state of iron is \(+3\). It also exists as the dihydrate, \(\mathrm{FePO}_{4} \cdot\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\).

Uses of Ferric Phosphate

The important uses of ferric phosphate are: 

1. It is used in the metal and steel manufacturing process.
2. It is used as a pesticide in the field of organic farming.
3. It is used as a food additive and a nutritional supplement.

Disodium Hydrogen Phosphate Formula

Disodium hydrogen phosphate is an inorganic compound with the chemical formula \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\). It is also known as disodium phosphate, sodium hydrogen phosphate or disodium hydrogen orthophosphate, etc. Let us discuss more about sodium hydrogen phosphate.

Disodium Hydrogen Phosphate [Na₂HPO₄]

The chemical formula of disodium hydrogen phosphate is \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\). It contains two sodium \(\left(\mathrm{Na}^{+}\right)\) cations and hydrogen phosphate, \(\left[\mathrm{HPO}_{4}\right]^{2-}\) anion. Disodium hydrogen phosphate can be represented as,

The molar mass of disodium hydrogen phosphate, \(\mathrm{Na}_{2} \mathrm{HPO}_{4}\) is \(141.96 \mathrm{~g} / \mathrm{mol}\).

Preparation of Disodium Hydrogen Phosphate

Disodium hydrogen phosphate can be prepared by the reaction of phosphoric acid with sodium hydroxide. That is,

\(\mathrm{H}_{3} \mathrm{PO}_{4}+2 \mathrm{NaOH} \rightarrow \mathrm{Na}_{2} \mathrm{HPO}_{4}+2 \mathrm{H}_{2} \mathrm{O}\)

The above reaction is an example of a neutralization reaction. 

Industrial preparation of disodium hydrogen phosphate. It involves two steps. That is,

Step 1: In the first step, dicalcium phosphate is treated with sodium bisulfate. As a result, calcium sulphate is formed. That is,

\(\mathrm{CaHPO}_{4}+\mathrm{NaHSO}_{4} \rightarrow \mathrm{NaH}_{2} \mathrm{PO}_{4}+\mathrm{CaSO}_{4}\)

Step 2: In the second step, the solution of monosodium phosphate is neutralized partially to obtain disodium hydrogen phosphate. That is,

\(\mathrm{NaH}_{2} \mathrm{PO}_{4}+\mathrm{NaOH} \rightarrow \mathrm{Na}_{2} \mathrm{HPO}_{4}+\mathrm{H}_{2} \mathrm{O}\)

Properties of Disodium Hydrogen Phosphate

Disodium hydrogen phosphate appears as a white crystalline solid. It is soluble in water but insoluble in alcohol. It is hygroscopic in nature. The solution of disodium hydrogen phosphate in water is moderately basic in nature. 

Disodium hydrogen phosphate, when heated, gives tetrasodium pyrophosphate. That is,

\(2 \mathrm{Na}_{2} \mathrm{HPO}_{4} \rightarrow \mathrm{Na}_{4} \mathrm{P}_{2} \mathrm{O}_{7}+\mathrm{H}_{2} \mathrm{O}\)

Uses of Disodium Hydrogen Phosphate

The major uses of disodium hydrogen phosphate are: 

1. It is used in water softening treatment.
2. It is used in puddings and desserts.
3. It is used in some cleaning agents and detergents.
4. It is used to treat constipation.
5. It can be used to inhibit the formation of calcium kidney stones.

Summary

We are now familiar with the term ‘phosphate’. It refers to an anion, a salt or several compounds derived from phosphoric acid. A phosphate ion has the chemical formula \(\mathrm{PO}_{4}^{3-}\). A hydrogen phosphate ion has the chemical formula \(\left[\mathrm{HPO}_{4}\right]^{2-}\). The compounds containing these ions can be found naturally in our biological systems. The other compounds containing the phosphate group are now discussed in detail: their formula, preparation, properties, and their uses.

FAQs on Phosphate Formula

Q.1. What is the formula for calcium phosphate?
Ans: Calcium phosphate is an inorganic compound with the chemical formula \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)_. It contains calcium \(\left(\mathrm{Ca}^{2+}\right)\) ions and phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) ions.

Q.2. What is the formula for magnesium phosphate?
Ans: Magnesium phosphate is an inorganic compound with the chemical formula \(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\). It contains magnesium \(\left(\mathrm{Mg}^{2+}\right)\) ions and phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) ions.

Q.3. What is the formula of zinc phosphate?
Ans: Zinc phosphate is an inorganic compound with the chemical formula \(\mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}\). It contains zinc \(\left(\mathrm{Zn}^{2+}\right)\) ions and phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) ions.

Q.4. Write the formula for sodium phosphate.
Ans: The chemical formula of sodium phosphate is \(\mathrm{Na}_{3} \mathrm{PO}_{4}\). It contains sodium \(\left(\mathrm{Na}^{+}\right)\) and phosphate \(\left(\mathrm{PO}_{4}^{3-}\right)\) ions.

Q.5. What is the formula of a phosphate ion?
Ans: The phosphate ion is an anion with the chemical formula \(\mathrm{PO}_{4}^{3-}\).

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