Citric acid is something we’ve probably come across in our kitchens or notified on food labels. It’s what gives lemons and oranges their sour taste. But citric acid isn’t just about flavor it also plays an important role in food, cleaning products and even in science and biology. In this article, we’ll explore what citric acid is, its formula, structure, IUPAC name, and how it’s used in everyday life and beyond.

Define Citric Acid?

Citric acid is a type of weak acid that has a chemical formula of \( C_{6}H_{8}O_{7} \). Citric acid is an organic compound. It is colourless, odourless, and sour in flavour. It occurs naturally in high quantities in all the citrus fruits. It has a structure of a monoclinic crystal. This acid was secluded for the first time by Swedish-German pharmaceutical chemist Carl Wilhelm Scheele in the year of 1784.

In biochemistry, it comes on an intermediate part in the citric acid cycle, which occurs in the metabolism of all aerobic living organisms. Since this is very similar in resemblance to table salt, it is sold as sour salt or lemon salt in the marketplace It is mainly present in two forms, which are as follows:

• Monohydrate (with one molecule of water), and
• Anhydrous (water-free).

A citrate is a derivative formed from a citric acid, which is generally present in the form of salts, esters, and the polyatomic anion which is found in a solution. An example of citrate is a salt which is trisodium citrate or an ester which is triethyl citrate. When citrate is a part of a salt, the formula of its anion is written as \( C_{6}H_{5}O_{7}^{3-} \) or \( C_{3}H_{5}O(COO)_{3}^{3-} \).

The molecular or the chemical formula of citric acid is \( C_{6}H_{8}O_{7} \) or it can also be written in an extended form as \( CH_{2}COOH-COHCOOH-CH_{2}-COOH \).

The image below shows the structure of citric acid and in it, the junctions represent the Carbon (C) bond with another C (carbon), OH (hydroxide), and O (oxygen).

From the above diagram, we can understand that citric acid has 6 carbon molecules, 8 hydrogen molecules, and 7 oxygen molecules. Here, the red spheres represent a carbon atom, grey spheres represent a hydrogen atom and blue spheres represent an oxygen atom.

What is the IUPAC name of Citric Acid? 

The IUPAC name or the scientific name of the citric acid is 2-hydroxypropane-1,2,3-tricarboxylic acid.

Molecular Weight of Citric Acid Formula

The molecular weight or the molar mass of citric acid is 192 g/mol. Since it has a molecular formula of \( C_{6}H_{8}O_{7} \), this means that one mole of citric acid has a mass of 192 g.

We can understand the way to calculate it from the method below:

Molar mass of \(C_6H_8O_7\) = 6* (Atomic mass of C) + 8 *(Atomic mass of H) + 7*(Atomic mass of O)

= 6*(12.01* g/mol) + 8*(1.008* g/mol) + 7(16.00 g/mol)

= 72.06* g/mol + 8.064* g/mol + 112* g/mol

= 192.124*g/mol

How Citric Acid is Made?

To understand how citric acid is produced, let’s look at its natural and industrial methods in the table below:

Chemical Properties of Citric Acid

Let’s now explore the Chemical properties of citric acid to see how it behaves in reactions, especially due to its acidic nature.

Physical Properties of Citric Acid

Understanding the physical properties of citric acid such as its appearance, melting point, and solubility helps build a clear foundation for its behaviour in various scientific applications.

Chemical Reactions of Citric Acid

The chemical reactions that take place in the formation of citric acid are written below:

Before that, we should know that it comes from a family of carboxylic acids. To form citric acid, the Acetyl CoA and Oxaloacetic Acid are condensed together to form Citric Acid. In addition to this, at the Ketone carbon, the Acetyl group which is \( CH_{3}COO \) is transferred to an Oxaloacetic Acid from CoA by the chemical reaction taking place. This is how citric acid is formed in nature other than in the human body. This process is called the citric acid cycle.

In the human body, citric acid is formed by the reaction aiming to make 2 carbon atoms moving with 4 carbon atoms, which results in the forming of this acid that has 6 carbon atoms present in it. This process is called the synthesis of acid in the human body.

The image below shows the citric acid cycle also known as the Krebs cycle in human beings:

What are the uses of Citric Acid?

The uses of citric acid are as follows:

• Citric acid is used as an antioxidant agent
• It is used as an emulsifying agent in ice creams as it keeps the fat globules away.
• It is used to add a sour taste to food items and soft drinks.
• It is present in edible food colours.
• It is also used in shampoos.
• It is used in the crystallization of sucrose in caramel
• It is used as a natural preservative which is added to the food to stop it from getting spoiled.
• It is used to remove the chalky deposit which is nothing but calcium build-up from the boilers, evaporators, kettles, water purifiers, etc.
• It is also used as a cleaning agent (as it is used as an ingredient in kitchen and bathroom cleaning solutions).
• It is used in the treatment process of hard water as it breaks down the trace quantities of metal ions found in the water, as due to these ions water becomes unfit for cleaning clothes.
• It is also in electroplating and leather tanning
• It is used in the process of storage of blood and its components.
• It is used as an antioxidant and buffer in the manufacturing of pharmaceutical and cosmetic products.
• It is also used as a chelating agent.
• It is used in deodorants and room fresheners.
• It is used in many cosmetic products nowadays as it helps in the removal of dead skin cells, wrinkles, acne scars, etc.

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