The Sodium phosphate is an inorganic salt whose chemical formula is Na3PO4. It is also called trisodium phosphate (TSP): Trisodium Phosphate), or tribasic sodium phosphate, because it completely lacks the ability to donate hydrogen ions H+.
When it is referred to in a plural way, sodium phosphates, it refers to the entire compendium of salts, hydrated or not, originating from electrostatic interactions between Na+ and the PO43-. Some of these salts even consist of sodium pyrophosphates, or inorganic polymers that have PO43- as monomer.
That is why, unless a specification is made, it will always refer to the Na3PO4, and not NaHtwoPO4, NatwoHPO4, Na4PtwoOR7 nor to any other salt.
The image above shows the appearance of sodium phosphate, which sports white crystals similar to common or table salt, or is purchased as a white amorphous-looking powder. The Na3PO4 is capable of forming various hydrates, being Na3PO412HtwoOr the one that is marketed the most.
It finds use mainly in the food industry, in detergents, sports supplements, and serves as a hyperosmotic laxative.
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The same formula Na3PO4 indicates that for each PO anion43- there are three Na cations+. These ions can be seen in the image above. Note that the PO43- has tetrahedral geometry, with its oxygen atoms carrying a resonant negative charge, which attracts the Na+ of the environment.
Likewise, the formula Na3PO4 points out that it is the anhydrous salt, so there are no water molecules included in its crystals. The electrostatic attractions between the Na+ and the PO43- they end up defining a trigonal white crystal. Its ionic bond is such that Na3PO4 has a melting point of 1583 ºC, considerably higher than that of various salts.
Both the Na+ as the PO43- They are ions that can be highly hydrated, without negatively affecting the stability of the crystals.
It is for this reason that hydrates can also crystallize; however, its melting points are lower than those of the anhydrous salt, since the intermolecular hydrogen bonds in water separate the ions and weaken their interactions. In the Na3PO412HtwoOr, for example, its melting point is 73.4 ºC, much lower than that of Na3PO4.
It can appear as defined white crystals or as a powder or granules of the same color. All the physical quantities expressed below refer only to the anhydrous salt Na3PO4.
1583 ºC
100 ºC
14.5 g / 100 mL at 25 ºC, which is why it is considered a phosphate quite soluble in water. However, it is insoluble in organic solvents such as ethanol and carbon disulfide..
2.536 g / cm3 at 17.5 ºC.
It is a hygroscopic solid. Therefore, it should be stored in such a way that it cannot be exposed to moisture.
It is a strongly alkaline salt. For example, a 0.1% aqueous solution thereof already has pH 11.5. This property serves to be used as an additive in detergents.
How is sodium phosphate produced or synthesized? To do this, we start from phosphoric acid, H3PO4, or of the sodium diacid phosphate salt, NaHtwoPO4.
In the vast majority of syntheses, H is preferred3PO4. Thus, the H is reacted3PO4 with a base that neutralizes its three OH groups, taking into account that this acid can also be written as PO (OH)3.
The base by preference is sodium hydroxide, NaOH (in Germany), but it is also feasible (and cheaper) to use sodium carbonate or soda ash, NatwoCO3 (in United States). The equations for both neutralization reactions are:
NatwoCO3 + H3PO4 → NatwoHPO4 + COtwo + HtwoOR
NatwoHPO4 + NaOH → Na3PO4 + HtwoOR
Note that when using NatwoCO3 Na is not obtained3PO4 but the NatwoHPO4, which will need a subsequent neutralization. As the reaction medium is aqueous, Na crystallizes3PO412HtwoOr, so it must be calcined to remove its water content and thus originate the anhydrous salt.
The Na3PO412HtwoOr it is characterized by "fusing" its crystals into a compact mass that is difficult to break. The smaller the size of your crystals, the faster their calcination will be.
In the uses of sodium phosphate it is inevitable to mix the Na3PO4 or to Na3PO412HtwoOr, since the latter is the hydrate that is most commercialized. For example, either of the two contributes harmless ions (in theory) to the foods to which they are added, enriching them with phosphates and increasing their salinity at the same time..
In the salt of the meats, the Na3PO412HtwoOr it's included to keep them fresh longer during storage. Likewise, it is added as an emulsifying agent so that the oil-water mixture does not "cut", but rather remains united; and as a pH regulator, as it helps reduce the acidity of foods (including cereals).
In addition, it is used to thicken some tomato sauces, and for baking cakes or breads (top image). The latter is due to the Na3PO412HtwoOr it tends to release water vapor, which increases the pore size and volume of the flour dough..
Sodium phosphate is basic enough to saponify some fats or oils that it comes in contact with. Its alkalinity is then used to improve the action of detergents, as long as the surface to be degreased is not metallic, as they can deteriorate it..
However, the production of detergents enriched with phosphates has been reduced due to the eutrophication of lakes and rivers and, with it, the proliferation of algae that cover their surfaces..
It has also been used to make a disinfectant: Na3PO41 / 4NaOCl11HtwoOr, which is prepared using sodium hypochlorite, NaOCl, instead of NaOH or NatwoCO3 to neutralize the H3PO4.
The Na3PO4 it induces defecation by acting as a hyperosmotic laxative, necessary to cleanse the colon before the patient undergoes a colonoscopy. On the other hand, it has also been used (added) in energy supplements.
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