Sodium Citrate Uses
Sodium citrate refers to sodium salts of citric acid. Monosodium citrate, disodium citrate, and trisodium citrate are the three types of sodium salts of citric acid. The three types of salts get collectively known as E number E 331. However, sodium citrate mostly refers to the third type, that is, trisodium citrate. Sodium citrate is a compound obtained after the alkalizing activity, and it’s a sodium salt of citrate. Its chemical formula is Na3C6H5O7. It gets majorly used in medicine as well as the food industry. In this article, you can learn about sodium citrate uses and the definition, frequently asked questions, etc.
What is Sodium Citrate?
It is a sodium salt of citrate, and it has an alkalinizing activity. You can also call it trisodium citrate. It gets widely used as a food preservative, anticoagulant for stored blood, and alkalization of urine to get rid of kidney stones. Sodium citrate formula is Na3C6H5O7. And below, you can see its structure.
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Properties of Sodium Citrate
Its molecular formula is Na3C6H5O7, and its molecular weight or molar mass is 258.068 g/mol.
Its appearance is white and comes in the form of crystalline powder, or granular crystals.
It’s soluble in water and becomes deliquescent upon contact with moist air. It’s insoluble in alcohol.
It has a sour taste like citric acid.
It has a total number of seven hydrogen bond acceptors and one hydrogen bond donor.
Monoisotopic mass of sodium citrate is 257.973 g/mol.
The melting point of sodium citrate is anywhere > (greater than) 3000 Celsius or 572 oF; 573K.
Applications of Sodium Citrate
Sodium citrate has major applications in food and beverage, healthcare, and other industrial ones too. Below you can read them in detail.
Food and Beverage:
Sodium citrate gets used as an emulsifying salt in processed cheese products. It facilitates the melting of cheese without becoming greasy. It works as a buffering agent in combination with citric acid, and it offers accurate pH control necessary for numerous foods and beverages. Its main job is being a food additive, either for flavor to improve taste or preservation purposes.
Healthcare:
Sodium citrate works perfectly as an anticoagulant for the blood. Thus, it gets widely used for blood collection and storage purposes. It can provide relief from the discomfort in urinary tract infections. It is also a great laxative and reduces several acidosis issues. It’s a significant ingredient of WHO’s oral rehydration solution. It also serves as an antacid, especially before anaesthesia.
You can easily find sodium citrate in many pharmaceutical products, colour, cosmetics, and deodorants. It’s also present in hair care, oral care, skincare, and bathing products.
Industrial Applications:
Citric acid gets used as an industrial cleaner. It helps with clearing steam blocks, hot water systems of calcium and rust layers. It also serves as a buffering and complexing agent in electroplating processes. Textile and building industry gets benefited by the chelating ability and non-toxicity of citric acid.
FAQs on Sodium Citrate
1. What is sodium citrate and what is its chemical formula?
Sodium citrate is the generic name for the sodium salts of citric acid. While there are three types, the term most commonly refers to trisodium citrate. It is produced by neutralizing citric acid with a source of sodium, such as sodium hydroxide. The chemical formula for the most common form, trisodium citrate, is Na₃C₆H₅O₇.
2. What are the key physical and chemical properties of sodium citrate?
Sodium citrate has several distinct properties relevant to its use in chemistry and industry:
- Appearance: It is a white, crystalline powder or comes in the form of granular crystals.
- Taste: It has a mild, saline, and slightly tart or sour flavour.
- Solubility: It is freely soluble in water but practically insoluble in alcohol.
- Hygroscopy: It is deliquescent, meaning it can absorb moisture from the air.
- Melting Point: It has a very high melting point, typically greater than 300°C, and it decomposes upon further heating.
3. What are the major applications of sodium citrate across different industries?
Sodium citrate is a versatile compound with important uses in several sectors:
- Food and Beverage Industry: Used as a food additive (E331) for flavouring (especially in club soda), as a preservative, an acidity regulator, and an emulsifying salt in products like processed cheese.
- Healthcare and Medicine: It functions as an anticoagulant for stored blood, an alkalizing agent to treat urinary tract infections and prevent kidney stones, and as an ingredient in oral rehydration solutions.
- Industrial Applications: Used as a buffering and complexing agent in electroplating, and as a non-toxic cleaner to remove calcium and rust scale from boilers and water systems.
4. How does sodium citrate act as an emulsifier in products like processed cheese?
Sodium citrate functions as an emulsifying salt in processed cheese by acting as a sequestrant. In natural cheese, milk proteins (casein) are bound together by calcium. When heated, these proteins can clump and separate from fats, creating a greasy or stringy texture. Sodium citrate's ions attach to the calcium ions, removing them from the protein structure. This makes the proteins more soluble and allows them to mix evenly with fat and water, resulting in the smooth, uniform melt characteristic of processed cheese.
5. Why is sodium citrate used as an anticoagulant in blood collection tubes?
Sodium citrate is an effective anticoagulant because it is a strong chelating agent. The blood clotting process, or coagulation cascade, is highly dependent on the presence of calcium ions (Ca²⁺). When blood is collected in a tube containing sodium citrate, the citrate ions bind firmly to the calcium ions, forming a calcium-citrate complex. By effectively removing the available calcium ions from the plasma, sodium citrate halts the clotting cascade, keeping the blood in a liquid state for laboratory analysis.
6. How does sodium citrate work as a buffering agent when combined with citric acid?
Sodium citrate, being the salt of a weak acid (citric acid), forms a highly effective buffer solution when mixed with citric acid. A buffer works by resisting changes in pH. In this system:
- If an acid (H⁺ ions) is added, the citrate ions (the conjugate base) will accept them, forming citric acid and preventing the pH from dropping significantly.
- If a base (OH⁻ ions) is added, the citric acid will donate a proton (H⁺) to neutralize the base, preventing the pH from rising sharply.
This ability to maintain a stable pH is crucial for controlling acidity in many foods, beverages, and pharmaceutical preparations.
7. Is sodium citrate considered safe for consumption in food and beverages?
Yes, sodium citrate is widely recognised by international food safety authorities, including the FDA, as Generally Recognized As Safe (GRAS) for consumption. It is approved as a food additive, often designated by the E number E331. Its roles as an acidity regulator, flavour enhancer, and emulsifier are well-established, and it is used in countless products, from soft drinks and jams to processed cheese and desserts, without posing a risk to health when consumed in standard amounts.
8. What are the main chemical differences between the three types of sodium citrate?
The difference lies in the degree of neutralization of citric acid, which is a triprotic acid (it has three donatable protons). The three types are:
- Monosodium citrate: Only one of the three acidic protons of citric acid has been replaced by a sodium ion (Na⁺).
- Disodium citrate: Two of the three acidic protons have been replaced by sodium ions.
- Trisodium citrate: All three acidic protons have been replaced by sodium ions.
This variation affects the molecule's overall charge, pH when dissolved in water, and specific applications. Trisodium citrate is the most common form and is what is generally referred to as 'sodium citrate'.
