The sodium citrate It is the sodium salt of citric acid. It is formed by a citrate anion C6H5OR73- and three sodium Na cations+. Its molecular formula is C6H5OR7Na3 or in its expanded form: NaOOC-CHtwo-C (COONa) (OH) -CHtwo-COONa. Sodium citrate is the conjugate base of citric acid, that is, it is theoretically obtained from the latter by substituting each H proton+ of -COOH for a sodium Na+.
It can be prepared in anhydrous form (without water in its composition) or in its hydrated form with 2 or 5 molecules of water. It is a compound that when anhydrous (without water) tends to absorb water from the environment.
Sodium citrate acts as a buffer, this means that it stabilizes the pH, which is a measure of the acidity or basicity of an aqueous solution. It also has the property of forming a stable compound with calcium Ca ions.two+, calcium citrate.
It is used in the food industry, for example, to prevent cow's milk from forming lumps that are difficult for infants to digest.
In bioassay laboratories it is used to prevent the blood taken from patients for certain tests from clotting. It also prevents blood used in transfusions from clotting. It is widely used in phosphate-free detergents because it is not polluting.
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Trisodium citrate is made up of three sodium Na ions+ and a citrate ion.
The citrate ion is made up of a chain of three carbon atoms to which 3 carboxylates are attached -COO- (one for each carbon atom) and a hydroxyl -OH at the central carbon.
Each of the 3 Na ions+ is attached to a -COO group-.
- Sodium citrate
- Trisodium citrate
- Trisodium 2-hydroxypropane-1,2,3-tricarboxylate
White or colorless crystalline solid.
258.07 g / mol
300 ºC
It is very soluble in water: 42.5 g / 100 mL at 25 ºC. It is practically insoluble in alcohol.
A 5% aqueous solution of sodium citrate has a pH between 7.5 and 9.0, that is, it is slightly alkaline.
Sodium citrate is a buffer, which means that it stabilizes the pH, which is a measure of the acidity or alkalinity of an aqueous solution. Citrate, by stabilizing the pH, does not allow the solution to acidify or alkalize above certain values.
When there are excess protons H+ takes them to convert their -COO groups- in -COOH groups. Vice versa, if there are many OH groups- gives up the protons of their -COOH groups and converts them to -COO-.
When it is transformed by the body, it provides 3 molecules of HCO3- for each citrate molecule.
Its crystals are deliquescent, that is, they absorb water from the air. Sodium citrate dihydrate is more stable in air.
If the dihydrate is heated, when it reaches 150 ºC it becomes anhydrous (without water).
Like citric acid, sodium citrate tastes sour.
Sodium citrate is usually made by adding sodium carbonate to a citric acid solution until effervescence ceases. The effervescence is due to the evolution of carbon dioxide COtwo:
NatwoCO3 + Citric acid → Sodium citrate + COtwo↑
Then the water is evaporated from the solution to crystallize the product.
It can also be prepared by treating a sodium sulfate solution with calcium citrate:
NatwoSW4 + Calcium citrate → Sodium citrate + CaSO4↓
The solution is filtered to remove the CaSO4 solid that has precipitated. Then the solution is concentrated and thus the sodium citrate crystallizes.
Sodium citrate is the conjugate base of citric acid, which is a natural compound found in all living organisms as it is part of their metabolism, which is the mechanism for developing energy in cells..
Sodium citrate has various uses in the food industry, for example, as an acidity regulator, sequestrant, stabilizer, surfactant or emulsifier..
It is used in drinks, frozen desserts and special cheeses, among other products.
It allows to avoid the coagulation of the milk, reason why it is added to the cow's milk that is used for the feeding of lactating children. In this way, clots or hard curds that are difficult to digest are not created by the stomach of children..
It is used to accelerate the color fixation in cured pork or beef, that is, meat that has been treated to prevent spoilage. Up to 50% ascorbic acid is replaced in these.
It is also used to prevent blood clotting in fresh beef (such as steaks)..
It is used as an alkalizing agent, as it neutralizes excess acid in the blood and urine. It is indicated to treat metabolic acidosis that occurs when the body produces too much acid.
Once ingested, the citrate ion becomes bicarbonate ion which is a systemic alkalizing agent (that is, of the whole organism) and as a consequence the H ions are neutralized.+, increases blood pH and reverses or eliminates acidosis.
Sodium citrate serves as a neutralizing agent for an upset stomach.
It is used as an expectorant and sudorific. It has diuretic action. Increases urinary calcium excretion, which is why it is used in hypercalcemia, which is when there is an excess of calcium in the blood.
It also serves to facilitate lead removal when lead poisoning occurs..
If administered in excess, it can cause alkalosis, muscle spasms due to malfunction of the parathyroid gland and depression of heart function due to a decrease in the level of calcium in the blood, among other symptoms..
Sodium citrate is used in transfusions. It is added to the blood together with dextrose to prevent it from clotting.
Normally the liver rapidly metabolizes the citrate obtained in the transfusion, however, during transfusions of large amounts, the liver's capacity may be exceeded..
In such cases, since citrate forms a complex with calcium, a decrease in the calcium ion Ca results.two+ in the blood. This can lead to lightheadedness, tremors, tingling, etc. Therefore transfusions must be performed slowly.
Among many other uses it is used to prevent the darkening of drugs in which there are iron and tannins.
It is used as an anticoagulant in blood collection or when it must be stored, as it acts as a chelator of calcium Ca ionstwo+, that is, it binds to calcium ions forming calcium citrate which is not ionized.
It is used in coagulation tests and in determining the sedimentation rate of red blood cells..
It is used as an anticoagulant during plasmapheresis, a procedure to remove excess substances harmful to the body from the blood.
It is used as a stabilizer in the synthesis of gold nanoparticles. Trisodium citrate dihydrate is added to chloroauric acid, forming a wine-red suspension..
Sodium citrate serves as a reducing agent and as an antiplatelet agent, as it adsorbs onto the nanoparticles..
Due to the negative charge of citrate the particles repel each other avoiding agglomeration and forming a stable dispersion. The higher the citrate concentration, the smaller the particles..
These nanoparticles are used to prepare medical biosensors.
Sodium citrate is widely used in phosphate-free liquid detergents. This is because its environmental behavior is harmless as it is a metabolite found in all living organisms..
It is easily biodegradable and weakly toxic to aquatic life. For this reason it is considered to be a cleaning agent with ecologically favorable characteristics..
Oil sands are sandy formations rich in bitumen or tar, a material similar to petroleum.
Sodium citrate has been successfully tested in conjunction with sodium hydroxide NaOH to extract oil from tar sands.
It is thought that when citrate binds with sandstone, the -COO ions- Citrate forms a large number of negative charges on silica particles. This produces a better separation of the sand from the bitumen by the simple repellency of the negative charges of the gravel from the negative charges of the bitumen.
It is used in photography, to remove trace metals, in electroplating and to remove SOtwo waste gases.
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