Citric acid is a natural acid found in citrus fruits. It’s widely used in food and beverages as a flavor enhancer and preservative. It also has applications in cleaning products and cosmetics.
| IUPAC Name | 2-hydroxypropane-1,2,3-tricarboxylic acid |
| Molecular Formula | C₆H₈O₇ |
| CAS Number | 77-92-9 |
| Synonyms | 3-carboxy-3-hydroxyglutaric acid, 2-hydroxy-1,2,3-propanetricarboxylic acid, citrate, and more |
| InChI | InChI=1S/C6H8O7/c7-3(8)1-6(13,5(11)12)2-4(9)10/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12) |
Citric Acid Properties
Citric Acid Formula
The formula of citric acid is C₆H₈O₇. It consists of six carbon atoms, eight hydrogen atoms, and seven oxygen atoms. This chemical formula represents the arrangement of atoms in a single molecule of citric acid.
Citric Acid Molar Mass
The molar mass of C₆H₈O₇ is approximately 192.13 grams per mole. It is calculated by adding up the atomic masses of all the atoms present in one mole of C₆H₈O₇. The molar mass is used to convert between grams and moles in chemical calculations.
Citric Acid Boiling Point
Citric acid does not have a distinct boiling point because it undergoes decomposition before it reaches a boiling temperature. However, when heated, it starts to degrade at around 175 degrees Celsius (347 degrees Fahrenheit). The decomposition of C₆H₈O₇ results in the formation of water and carbon dioxide.
Citric Acid Melting Point
Citric acid has a melting point of 153 degrees Celsius (307 degrees Fahrenheit). At this temperature, the solid form of C₆H₈O₇ converts into a liquid. It is important to note that C₆H₈O₇ can also exist in an anhydrous form, which has a higher melting point of around 310 degrees Celsius (590 degrees Fahrenheit).
Citric Acid Density g/mL
The density of C₆H₈O₇ is approximately 1.665 grams per milliliter (g/mL). This value represents the mass of C₆H₈O₇ contained in one milliliter of volume. The density of a substance is often used to determine its concentration or purity.
Citric Acid Molecular Weight
The molecular weight of C₆H₈O₇ is approximately 192.13 grams per mole. It is the sum of the atomic weights of all the atoms in one molecule of C₆H₈O₇. The molecular weight is an important parameter for various chemical calculations and reactions.
Citric Acid Structure
Citric acid has a tricarboxylic acid structure with three carboxyl (-COOH) functional groups. It contains a central carbon atom bonded to three carboxyl groups and a hydroxyl group (-OH). The arrangement of atoms gives C₆H₈O₇ its characteristic acidic properties and enables it to participate in various biochemical processes.
Citric Acid Solubility
Citric acid is highly soluble in water. It readily dissolves in water, alcohol, and other polar solvents. The solubility of C₆H₈O₇ increases with temperature. It is commonly used as a food additive and flavoring agent due to its ability to dissolve and enhance flavors in aqueous solutions.
| Appearance | White crystalline powder |
| Specific Gravity | 1.665 |
| Color | Colorless or white |
| Odor | Odorless |
| Molar Mass | 192.13 g/mol |
| Density | 1.665 g/mL |
| Melting Point | 153 °C (307 °F) |
| Boiling Point | Decomposes before boiling |
| Flash Point | Not applicable |
| Water Solubility | Highly soluble |
| Solubility | Soluble in water, alcohol, and polar solvents |
| Vapour Pressure | Not applicable |
| Vapour Density | Not applicable |
| pKa | pKa₁ = 3.13, pKa₂ = 4.76, pKa₃ = 6.40 |
| pH | pH = 1.8 – 3.1 (1% solution at 25 °C) |
Citric Acid Safety and Hazards
Citric acid is generally recognized as safe for consumption and has a low toxicity level. However, handling it requires some precautions. It can cause eye and skin irritation, so wearing protective gloves and goggles is recommended. Inhaling C₆H₈O₇ dust or mist may irritate the respiratory system, so working in well-ventilated areas is advised. While it is not flammable, high temperatures can cause C₆H₈O₇ to decompose and release irritating fumes. It is important to store C₆H₈O₇ in a cool, dry place away from incompatible substances. Overall, practicing good safety measures ensures safe handling of C₆H₈O₇.
| Hazard Symbols | None |
| Safety Description | Causes eye and skin irritation. May cause respiratory irritation. Handle with care and avoid inhalation |
| UN IDs | Not applicable |
| HS Code | 2918.14.00 |
| Hazard Class | Not classified as hazardous |
| Packing Group | Not applicable |
| Toxicity | Low toxicity; generally recognized as safe |
Citric Acid Synthesis Methods
Various methods can synthesize C₆H₈O₇.
Microorganisms like certain strains of the fungus Aspergillus niger or the bacterium Escherichia coli ferment carbohydrates like glucose or sucrose in a nutrient-rich medium to synthesize C₆H₈O₇ as a byproduct. They metabolize the sugars, producing C₆H₈O₇ during fermentation.
Citrus fruits are initially juicing to obtain a concentrated solution, extracting C₆H₈O₇ from natural sources. The purification processes eliminate impurities and solid particles from the juice. Treating the concentrated solution with calcium hydroxide forms calcium citrate, a salt of C₆H₈O₇. Acidifying the solution using sulfuric or hydrochloric acid releases C₆H₈O₇ as a precipitate from this salt. Collecting, washing, and drying the precipitate yields pure C₆H₈O₇.
Chemical synthesis methods involve the catalytic oxidation of glucose or other carbohydrates using specific catalysts like platinum or palladium. Glucose is converted to gluconic acid through this process, and further oxidation converts it to C₆H₈O₇.
Overall, these processes enable the large-scale production of C₆H₈O₇ to fulfill the demand in various industries such as food and beverage, pharmaceuticals, and cosmetics.
Citric Acid Uses
C₆H₈O₇ finds numerous applications across various industries due to its versatile properties. Here are some common uses:
- Food and Beverage Industry: The food and beverage industry widely utilizes C₆H₈O₇ as a flavor enhancer, acidulant, and preservative in soft drinks, jams, candies, and dairy products.
- Pharmaceutical Industry: The pharmaceutical industry uses C₆H₈O₇ as a pH adjuster and flavoring agent in the production of effervescent tablets and syrups. It also serves as a chelating agent in certain medications.
- Cleaning Products: C₆H₈O₇ effectively removes limescale, hard water stains, and rust, making it a common ingredient in household cleaners, dishwashing detergents, and descaling agents.
- Cosmetics and Personal Care: C₆H₈O₇ plays multiple roles in skincare and hair care products, serving as a pH adjuster, exfoliant, and enhancing the effectiveness of other ingredients.
- Water Treatment: C₆H₈O₇ finds application in water treatment processes to control pH levels and eliminate metal ions. It aids in preventing scale formation and inhibiting the growth of certain bacteria.
- Industrial Applications: Various industries employ C₆H₈O₇ in processes such as metal cleaning, textile dyeing, and catalyzing chemical reactions.
- Photography: In photography, developers use C₆H₈O₇ in developing solutions for photographic films. It helps control pH and improves image quality.
- Flavoring and Food Preservation: C₆H₈O₇’s tangy flavor makes it a popular choice as a souring agent in food products. Additionally, it acts as a natural preservative, extending the shelf life of certain foods.
These diverse applications highlight the significance of C₆H₈O₇ in numerous industries, making it a valuable and widely used compound.
Questions:
Q: What is citric acid?
A: C₆H₈O₇ is a natural acid found in citrus fruits like lemons and oranges, and it is widely used in various food and industrial applications.
Q: Is citric acid a natural preservative?
A: Yes, C₆H₈O₇ is commonly used as a natural preservative due to its ability to inhibit the growth of certain bacteria and prolong the shelf life of food products.
Q: Is citric acid bad for you?
A: C₆H₈O₇ is generally recognized as safe for consumption in moderate amounts, but excessive intake may cause gastrointestinal discomfort or tooth erosion.
Q: Is citric acid and ascorbic acid the same?
A: No, C₆H₈O₇ and ascorbic acid (vitamin C) are different compounds with distinct chemical structures and properties, although both are commonly found in fruits.
Q: Is citric acid dangerous?
A: C₆H₈O₇ is not inherently dangerous when used appropriately, but it can cause eye and skin irritation, and inhalation of large amounts of citric acid dust or mist may irritate the respiratory system.
Q: Where does the citric acid cycle occur?
A: The C₆H₈O₇ cycle, also known as the Krebs cycle, occurs in the mitochondria of cells and plays a central role in cellular respiration, producing energy-rich molecules.
Q: Which of these enters the citric acid cycle?
A: Acetyl-CoA, a molecule derived from the breakdown of carbohydrates, fats, and proteins, enters the C₆H₈O₇ cycle to be further metabolized and generate energy.
Q: Is citric acid bad for you?
A: C₆H₈O₇ is generally safe for consumption in moderation, but excessive intake may lead to adverse effects, such as gastrointestinal discomfort and tooth enamel erosion.