What Is Lactic Acid? Key Facts, Structure, and Applications
Lactic acid, also known as lactate, is a chemical byproduct of anaerobic respiration. It refers to a process where cells produce energy without having oxygen around. Lactic acid gets produced in yoghurt by some bacteria. It is also present in your gut and blood. Your muscles and red blood cells often deposit the lactate into your blood. So, lactic acid is an organic one. It’s a chiral molecule, and it has two optical isomers, which are L-lactic acid and D-lactic acid. The presence of a carboxyl group adjacent to the hydroxyl group makes lactic acid an alpha-hydroxy acid. In this article, you can learn about lactic acid structure, its definition, uses, and sources.
What is Lactic Acid?
Lactic acid is one of the organic acids. The chemical formula of the lactic acid is C3H6O3. It has two optical isomers, Levo and Dextro, making itself a chiral molecule. L-isomers are commonly present among living organisms. The lactic acid has a significant part in various biochemical processes. It gets produced by the muscles during intense activity.
Lactic acid is soluble in water. It looks white in its solid-state and becomes colourless in the liquid state. Milk acid is another name of lactic acid. When lactose or milk sugar undergoes fermentation, the lactic acid gets produced. You can also find it in other dairy products like cottage cheese, yoghurt, etc.
Just so you know, a Swedish chemist, named Carl Wilhelm Scheele, isolated the lactic acid from milk for the first time in 1780. Also, the soluble salt of lactic acid, such as calcium lactate can act as a source of calcium. The PH of 1 mM of lactic acid is nearly 3.51. You can learn more about lactic acid as below.
Structure of Lactic Acid
Below you can find the structural representation of lactic acid or C3H6O3.
(Images to be added soon)
The extended formula of lactic acid is CH3CH(OH)CO2H, and it has a molar mass of 90.08 g/mol. Since a single carbon houses hydroxyl group (-OH) and carboxylic group (-COOH), the molecule gets classified as alpha-hydroxy acid. The central carbon is a chiral as it appears and the other two substituent groups are a hydrogen atom on a methyl group (-CH3). It results in two different structures: L-lactic acid (+) and D-lactic acid (-).
Properties of Lactic Acid
Lactic acid is colorless or yellow syrupy, during its liquid state. In solid form, you can find it in the white powder.
The molecular weight or molar mass of lactic acid is 90.08 g/mol. And it’s PH level is 3.51 per 1 mM of lactic acid.
The melting point of lactic acid is 530 Celsius, and the boiling point is 1220 Celsius. It is soluble in water and ethanol.
Lactic acid is corrosive to any metals and tissue. Thus, overuse and overconsumption of the lactic acid can come with severe side effects.
Uses of Lactic Acid
There are numerous lactic acid uses, and the first thing to note is that your body can produce lactic acid on its own. But, there is a significant requirement for industrially produced lactic acid. It can get formed using a synthetic process or fermentation. The latter involves usage of nutrients like amino acids, vitamins, peptides, glucose, and salt. These nutrients get combined with microbes, which further uses nutrients to give out lactic acid.
Once the lactic acid is ready, it can be used for various purposes as below.
Personal products and healthcare products
Food preservatives
Dairy products, like yoghurt
Cleaning, laundry, and dishwashing products
Paint and coating additives
Furniture care products
Textile dyeing and leather tanning
Pharmaceuticals
Applications of Acids and Basic Substances
Due to the different properties of acids and bases, they have a significant role in real-life applications. Some of the applications are-
Applications of Acid Substances
Citric acid is a key ingredient in lemons and oranges. Acids can also be utilized to preserve food.
Sulfuric acid is widely used in car batteries, which are commonly used to start the engines of automobiles.
Acids are used in the industrial production of explosives, dyes, and fertilizers.
Phosphoric acid is one of the key ingredients in many soft drinks.
Vinegar is a diluted form of acetic acid and it features several home applications like preserving food, etc.
Applications of Basic Substances
Ammonium hydroxide is one of the most important reagents used in laboratories.
Any extra acidity in the ground (soil), could be neutralized by utilizing slaked lime.
Ca(OH)2 (also known as slaked lime or calcium hydroxide) is used to make dust which is used for bleaching powder.
Calcium Hydroxide is used to make dry mixes which are utilized in design or artwork.
The production of soap and paper requires the utilization of salt (sodium hydroxide).
NaOH is utilized in the making of rayon.
Magnesium hydroxide(also referred to as milk of magnesia) is usually used as a laxative and it also decreases any extra acidity in a human's stomach. This property qualifies it to be an antacid.
FAQs on Lactic Acid Explained: Formula, Properties & Uses
1. What is lactic acid, and what is its chemical formula?
Lactic acid is an organic acid that plays a role in various biochemical processes. It is produced naturally in our muscle cells during strenuous exercise and by certain bacteria during fermentation. The chemical formula for lactic acid is C₃H₆O₃. It is also known as milk acid because it was first isolated from sour milk.
2. What is the IUPAC name and structure of lactic acid?
The IUPAC name for lactic acid is 2-hydroxypropanoic acid. Its structure consists of a three-carbon propanoic acid backbone with a hydroxyl group (-OH) attached to the second carbon (the alpha-carbon). This makes it an alpha-hydroxy acid (AHA).
3. What are the key physical and chemical properties of lactic acid?
Lactic acid has several distinct properties:
Appearance: It is a colourless or yellowish syrupy liquid in its aqueous state and a white powder in its solid form.
Solubility: It is miscible with water and ethanol.
Acidity: As a carboxylic acid, it is a weak acid with a pKa of about 3.86.
Chirality: It is a chiral molecule and exists as two optical isomers (enantiomers).
Molar Mass: The molar mass of lactic acid is approximately 90.08 g/mol.
4. Why is lactic acid considered a chiral molecule? Explain its importance.
Lactic acid is considered chiral because its central carbon atom (C2) is attached to four different groups: a hydrogen atom (-H), a carboxyl group (-COOH), a hydroxyl group (-OH), and a methyl group (-CH₃). This asymmetric carbon centre allows for the existence of two non-superimposable mirror images, known as enantiomers:
L-(+)-lactic acid: The biologically active form found in the human body.
D-(-)-lactic acid: Produced by certain bacteria.
This chirality is crucial because enzymes in biological systems are stereospecific and typically interact with only one of these forms.
5. How and why does lactic acid build up in muscles during intense exercise?
During intense physical activity, the body's demand for energy exceeds the oxygen supply available to the muscle cells. To compensate, the muscles switch from aerobic (with oxygen) to anaerobic respiration (without oxygen). In this process, glucose is broken down into pyruvate, which is then converted into lactate to quickly generate ATP (energy). This rapid production of lactate leads to its accumulation, causing the characteristic burning sensation and fatigue in muscles.
6. What is the difference between the terms 'lactic acid' and 'lactate'?
While often used interchangeably, 'lactic acid' and 'lactate' are chemically distinct. Lactic acid (C₃H₆O₃) is a weak acid that can donate a proton (H⁺). When it loses this proton, it forms its conjugate base, which is called lactate (C₃H₅O₃⁻). At the physiological pH of the human body (around 7.4), it exists predominantly in its deprotonated form as lactate, not as the intact acid.
7. What are some of the important industrial uses of lactic acid?
Lactic acid is a versatile compound with several important applications:
Food and Beverage: It is used as a food preservative, curing agent, and flavouring agent. It provides the tangy taste in products like sourdough bread, yoghurt, and pickled vegetables.
Cosmetics: As an alpha-hydroxy acid (AHA), it is widely used in skincare products for exfoliation and improving skin texture.
Pharmaceuticals: It is used in IV solutions and for drug delivery systems.
Bioplastics: It is a key monomer for producing polylactic acid (PLA), a biodegradable and compostable plastic.
8. Which common foods are natural sources of lactic acid?
Lactic acid is found in a wide variety of foods, typically as a result of fermentation by lactic acid bacteria. Some common examples include fermented dairy products like yoghurt, kefir, and certain cheeses, as well as fermented vegetables and grains such as sauerkraut, kimchi, pickles, and sourdough bread.
9. How does lactic acid's structure allow it to undergo reactions of both alcohols and carboxylic acids?
Lactic acid is a bifunctional molecule, meaning it contains two different functional groups: a hydroxyl (-OH) group and a carboxyl (-COOH) group. This unique structure allows it to participate in reactions characteristic of both classes of compounds:
As a carboxylic acid: It can undergo esterification with an alcohol, or neutralization with a base.
As an alcohol: Its hydroxyl group can be oxidized or can react with a carboxylic acid to form an ester. It can also undergo self-esterification to form a cyclic dimer called lactide.
