Lactic Acid (C₃H₆O₃) — Properties, Uses & Safety

Overview

Lactic acid (C3H6O3), systematically named 2-hydroxypropanoic acid, is a hydroxy acid with a molar mass of 90.08 g/mol. It appears as a colorless to yellowish viscous liquid that is miscible with water. The molecule contains both a hydroxyl group (–OH) and a carboxylic acid group (–COOH) on adjacent carbons, with a chiral center at carbon-2 that gives rise to two enantiomers: L-lactic acid (produced by human metabolism) and D-lactic acid (produced by certain bacteria). Lactic acid is perhaps best known for its role in muscle fatigue — during intense anaerobic exercise, when oxygen supply cannot meet demand, the body converts pyruvate to lactate via anaerobic glycolysis, causing the familiar burning sensation in overworked muscles. This process is a key topic in biochemistry and exercise physiology. Lactic acid is also produced by bacterial fermentation of lactose and other sugars, a process responsible for the tangy flavor of yogurt, cheese, sauerkraut, kimchi, and sourdough bread. Industrially, lactic acid is used in food preservation, as a pH regulator, in cosmetics (as an alpha-hydroxy acid for skin exfoliation), and increasingly as the monomer for polylactic acid (PLA) — a biodegradable bioplastic made from renewable resources like corn starch. GHS hazard codes include H315 (causes skin irritation) and H318 (causes serious eye damage), with the corrosion pictogram. For chemistry students, lactic acid illustrates chirality and optical isomerism, the connection between organic chemistry and biochemistry, fermentation as a chemical process, carboxylic acid and alcohol functional groups in the same molecule, and the growing field of green chemistry through biodegradable polymer production. It makes abstract concepts like chirality and metabolic pathways tangible through everyday experiences like exercise and food.

IUPAC Name

2-hydroxypropanoic acid

CAS Number

50-21-5

PubChem CID

107689

Molecular Formula

C₃H₆O₃

Molar Mass

90.078 g/mol

State at STP

liquid

Appearance

Colorless to yellowish viscous liquid