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Sodium hydrogen phosphate Formula – Structure, Properties, Uses, Sample Questions

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  • Last Updated : 13 Jun, 2022
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Sodium hydrogen phosphate consists of elements Sodium, Hydrogen, Phosphorus, and Oxygen. Sodium is a silvery-white, soft, highly reactive alkali metal. It is present in group-1 of the periodic table. Its atomic number is 11 and is represented by the symbol Na. Hydrogen is the lightest, colorless, tasteless, and flammable gas. Its atomic number is one and is represented by the symbol H. Phosphorus is a highly reactive nonmetal present in group-15 of the periodic table. Its atomic number is 15 and is represented by the symbol P. Oxygen is a highly reactive nonmetal present in the chalcogen group, i.e., group-16. Its atomic number is eight and is represented by the symbol O.

Sodium hydrogen phosphate

Sodium hydrogen phosphate is an inorganic and hygroscopic compound with the chemical formula Na2HPO4. Sodium hydrogen phosphate has a saline taste. In anhydrous form, it appears as a white, odorless powder. In hydrated form, it appears as a white, odorless crystalline solid. Sodium hydrogen phosphate is soluble in water but insoluble in alcohol. The other names for the Sodium hydrogen phosphate formula are the Disodium phosphate formula or Sodium phosphate dibasic formula.

Preparation of Sodium hydrogen phosphate

Sodium hydrogen phosphate is obtained by neutralizing phosphoric acid (H3PO4) with sodium hydroxide (NaOH).

H3PO4 + 2NaOH → Na2HPO4 + 2H2O

In the above given reaction, when one molecule of Phosphoric Acid reacts with 2 molecules of Sodium Hydroxide then it produces one molecule of Sodium Hydrogen Phosphate and 2 molecule of Water.

At the industry scale, Sodium hydrogen phosphate is prepared in two steps,

  • Step 1: Dicalcium phosphate (CaHPO₄) is treated with sodium bisulfate (NaHSO4) to give precipitated calcium sulfate (CaSO4).

CaHPO4 + NaHSO4 → NaH2PO4 + CaSO4

In the above given reaction, when one molecule of Dicalcium Phosphate reacts with one molecule of Sodium Bisulfate then it produces one molecule of Monosodium Phosphate and Calcium Sulfate.

  • Step 2: The resultant monosodium phosphate (NaH2PO4) solution is neutralized partially.

NaH2PO4 + NaOH → Na2HPO4 + H2O

In the above given reaction, when one molecule of Monosodium Phosphate reacts with one molecule of Sodium Hydroxide then it produces one molecule of Sodium Hydrogen Phosphate and 1 molecule of Water.

Structure of Sodium hydrogen phosphate

Sodium Hydrogen Phosphate Structure

Physical Properties of Sodium hydrogen phosphate

  • The chemical formula for Sodium hydrogen phosphate is Na2HPO4.
  • It appears in Crystalline solid form.
  • The molecular weight of Sodium hydrogen phosphate is 141.96 g/mol.
  • The melting point of Sodium hydrogen phosphate is 250°C.
  • The density of Sodium hydrogen phosphate is 1.7 g/cm3.

Chemical Properties of Sodium hydrogen phosphate

  • On heating, sodium hydrogen phosphate gives a useful inorganic compound called tetrasodium pyrophosphate, a white, inorganic, water-soluble solid. Its chemical reaction of it is given below-

2Na2HPO4 → Na4P2O7 + H2O

Uses of Sodium hydrogen phosphate

  • Sodium hydrogen phosphate is used in food and water softening treatment.
  • It is used as a saline laxative to treat constipation (or) clean the bowel before a colonoscopy.

Sample Questions

Question 1: Is Sodium hydrogen phosphate is ionic or covalent compound?

Answer:

Sodium hydrogen phosphate is an ionic compound. Here Sodium is a metal with a +1 charge on each sodium atom and hydrogen phosphate is a nonmetal with -2 charge. We know that ionic compound is formed between oppositely charged ions. So it is an ionic compound.

Question 2: How Sodium hydrogen phosphate is used in foods?

Answer:

Using of Sodium hydrogen phosphate prevents the coagulation in the preparation of condensed milk. It also adjust the pH of food. In powdered products, It is used as an anti-caking additive. 

Question 3: Find the molecular weight of Na2HPO4?

Answer:

Atomic weight of each Sodium = 22.989769 

Atomic weight of each Hydrogen = 1.00784 

Atomic weight of Phosphorus = 30.973762 

Atomic weight of each Oxygen = 15.999 

Molecular weight of Na2HPO4 = (2 × 22.989769) + 1.00784 + 30.973762 + (4 × 15.999)

= 141.96

Question 4: What happens when Sodium hydrogen phosphate is heated?

Answer:

On heating the Sodium hydrogen phosphate gives an useful inorganic compound called tetrasodium pyrophosphate (Na4P2O7)

2Na2HPO4 → Na4P2O7 + H2O

Question 5: Is Sodium hydrogen phosphate health-hazardous?

Answer:

It causes mild irritation to skin when it is absorbed by skin. Inhaling the Sodium hydrogen phosphate may cause respiratory tract irritation.

Question 6: How Sodium hydrogen phosphate is prepared?

Answer:

Sodium hydrogen phosphate is simple prepared by neutralizing phosphoric acid (H3PO4) with sodium hydroxide (NaOH).

H3PO4 + 2NaOH → Na2HPO4 + 2H2O

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