A sodium phosphate is a generic variety of

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

s of

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

() and

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

(). Phosphate also forms families or condensed

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s including di-, tri-, tetra-, and

polyphosphate A polyphosphate is a Salt (chemistry), salt or ester of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic (also called, ring) structure ...

s. Most of these salts are known in both

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

(water-free) and hydrated forms. The hydrates are more common than the anhydrous forms.

Uses

Sodium phosphates have many applications in food and for water treatment. For example, sodium phosphates are often used as

emulsifier An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Althou ...

s (as in

processed cheese Processed cheese (also known as process cheese; related terms include cheese food, prepared cheese, cheese product, and/or government cheese) is a product made from cheese mixed with an emulsifying agent (actually a calcium chelator). Additiona ...

thickening agent A thickening agent or thickener is a substance which can increase the viscosity of a liquid without substantially changing its other properties. Edible thickeners are commonly used to thicken sauces, soups, and puddings without altering their ...

s, and

leavening agent In cooking, a leavening agent () or raising agent, also called a leaven () or leavener, is any one of a number of substances used in doughs and batters that cause a foaming action (gas bubbles) that lightens and softens the mixture. An altern ...

s for baked goods. They are also used to control pH of processed foods. They are also used in medicine for

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the ...

and to prepare the bowel for medical procedures. They are also used in detergents for softening water and as an efficient anti-

rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

solution.

Adverse effects

Sodium phosphates are popular in commerce in part because they are inexpensive and because they are nontoxic at normal levels of consumption. However, oral sodium phosphates when taken at high doses for

bowel preparation Colonoscopy () or coloscopy () is a medical procedure involving the Endoscopy, endoscopic examination of the large bowel (colon) and the distal portion of the small bowel. This examination is performed using either a Charge-coupled device, CCD ...

for

colonoscopy Colonoscopy () or coloscopy () is a medical procedure involving the Endoscopy, endoscopic examination of the large bowel (colon) and the distal portion of the small bowel. This examination is performed using either a Charge-coupled device, CCD ...

may in some individuals carry a risk of kidney injury under the form of phosphate nephropathy. There are several oral phosphate formulations which are prepared extemporaneously. Oral phosphate prep drugs have been withdrawn in the United States, although evidence of causality is equivocal. Since safe and effective replacements for phosphate purgatives are available, several medical authorities have recommended general disuse of oral phosphates.

Monophosphates

Three families of sodium monophosphates are common, those derived from orthophosphate (), hydrogen phosphate (), and dihydrogenphosphate (). Some of the best known salts are shown in the following table.

Di- and polyphosphates

In addition to these phosphates, sodium forms a number of useful salts with

pyrophosphate In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate () and tetrasodium pyrophosphate (), among others. Often pyrophosphates a ...

s (also called diphosphates), triphosphates and high polymers. Of these salts, those of the diphosphates are particularly common commercially. Beyond the diphosphates, sodium salts are known triphosphates, e.g.

sodium triphosphate Sodium triphosphate (STP), also sodium tripolyphosphate (STPP), or tripolyphosphate (TPP),

and tetraphosphates. The cyclic polyphosphates, called metaphosphates, include the trimer sodium trimetaphosphate and the tetramer, and , respectively. Polymeric sodium phosphates are formed upon heating mixtures of and , which induces a

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

. The specific polyphosphate generated depends on the details of the heating and annealing. One derivative is the

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

y (i.e., amorphous) Graham's salt (

sodium hexametaphosphate Sodium hexametaphosphate (SHMP) is a salt (chemistry), salt of composition . Sodium hexametaphosphate of commerce is typically a mixture of metaphosphates (empirical formula: NaPO3), of which the hexamer is one, and is usually the compound referr ...

). It is a cyclic polyphosphate with the formula . Crystalline high molecular weight polyphosphates include Kurrol's salt and Maddrell's salt (CAS#10361-03-2). These species have the formula where ''n'' can be as great as 2000, and it is a white powder practically insoluble in water. In terms of their structures, these polymers consist of units, with the chains are terminated by protonated phosphates.

References

External links

* * {{Phosphates Phosphates Sodium compounds Edible thickening agents