Sodium Phosphate Chemistry Guide and Properties

Sodium phosphate is an ionic compound composed of sodium cation and phosphate anion. This is a salt found both in hydrated and anhydrous salts among which anhydrous (water-free) sodium phosphate is more common in nature. The sodium phosphate chemical formula is Na₃PO₄ and it has a molecular weight of 163.94 g/mol. Besides sodium monophosphate, sodium diphosphate, triphosphate, tetraphosphate, and polyphosphates are also found in nature. As it is an ionic compound, it forms crystal structures. It appears as white or off-white crystals, granules, or maybe in powdered form. It has a density of 2.536 g/cc. Its boiling point is 373 k, just like water, and its melting point is 1856 K.

Structure of Sodium Phosphate

Sodium phosphate is an ionic compound and so exhibits an electrovalent chemical structure. The phosphate anion itself consists of a covalent structure. Sodium atoms have a total of 11 electrons of which one is in its outermost shell as sodium is an alkali metal. Sodium readily expels the outermost electron to produce sodium cation. Three Na⁺ and one PO₄^3- get attracted to each other using the electrostatic force of attraction and a sodium phosphate molecule is generated. 

Different Types of Sodium Phosphate

Although trisodium monophosphate (Na₃PO₄) is much more common, besides this, many types of sodium phosphates are found. These are disodium phosphate or disodium hydrogen phosphate, monosodium phosphate or sodium dihydrogen phosphate, disodium pyrophosphate, and tetrasodium pyrophosphate, which have the molecular formulas of Na₂HPO₄, NaH₂PO₄, Na₂H₂P₂O₇, and Na₄P₂O₇, respectively.

Trisodium phosphate is prepared in the laboratory by a simple reaction of sodium hydroxide or caustic soda with phosphoric acid. Three molecules of sodium hydroxide are neutralised with tribasic orthophosphoric acid (H₃PO₄) to produce trisodium phosphate salt and water.

H₃PO₄ + 3NaOH → Na₃PO₄+ 3H₂O

Disodium phosphate is industrially prepared by the action of dicalcium phosphate on sodium bisulfate. Disodium pyrophosphate is prepared by the thermal decomposition of monosodium phosphate.

Uses of Sodium Phosphate in Industry

The most common sodium phosphate, trisodium monophosphate is mostly used as detergents, soaps, and fertilizers. It acts as a preservative in the processing of animals’ foods. Trisodium phosphate, along with disodium and monosodium phosphate, are used mostly as food additives. They are used as emulsifiers in processed cheese in the dairy industry. It is also used as a thickening agent in the bakery industry. Disodium pyrophosphate is used as a buffer. Besides, it is used in the processing of canned seafood to maintain its taste and color. It is also used in leather industries to get rid of stains from hides. Tetrasodium pyrophosphate is also used in the processing of canned foods as a food additive and preservative. Tetrasodium pyrophosphate has the unique quality of removing magnesium from the saliva so that it can reduce the accumulation of dental plaques and cavities. So this compound is uniquely used among phosphates in toothpaste. 

Adverse Effects of the Use of Phosphates in Industry

Phosphates are mostly responsible for the eutrophication of water. It is a process by which water bodies receive excess phosphates that stimulate increased algal growth, called an algal bloom. It ultimately leads to the decomposition of algae so that the oxygen content of the water gets reduced. Phosphates used as detergents and soaps are mainly responsible for eutrophication as they are washed off and mixed in ponds, rivers, or lakes. For this reason, the usage of phosphates as detergent or fertilisers becomes limited. 

Medicinal Uses of Phosphates

Sometimes, phosphates are used in the preparation of medicines of constipation that is used to clear the bowels off, but the usage of phosphate in medicine industries is not safe. Phosphates can increase the risk of kidney problems in case of application of high dosage. This symptom is referred to as the medical terminology phosphate nephropathy. So their use in high dosage is not safe at all.

Sodium Tripolyphosphate

Sodium polyphosphate has the molecular formula Na₅P₃O₁₀. It has a molecular mass of 367.86 g/mol. It is prepared by heating the mixture of sodium dihydrogen phosphate and disodium hydrogen phosphate. These two get condensed, remove water, and produce sodium tripolyphosphate. 

Did you know?

• Sodium phosphate is mostly made from phosphate rocks of mine.

• Consumption of regular and long-term dosages of sodium phosphate becomes unhealthy for health.

• Although sodium phosphate is thought to be safe by FDA (Food and Drug Administration) in processed foods, where it is used as preservatives, patients with kidney disease should avoid foods containing sodium phosphate.

• Consumption of a high dosage of sodium phosphate causes reduced bone density, kidney problems, heart disease, and even early death.

• When sodium phosphate is consumed by mixing with other phosphates, it will help to fortify phosphorus in the body.

• Meats, beans, lentils, and nuts are good sources of phosphates.

• Phosphate can increase the growth of algae 500 times of its normal growth in a water body. 

• Graham’s salt, Kurrol’s salt, and Madrell’s salt are the derivatives of polyphosphate. 

• Oral sodium phosphate should not be used as a laxative under 5 years of age.

Conclusion

Sodium phosphate is one of the important formulas that is used for many purposes. It can be for medical use or it might be used for fooding and preserving purposes.