Science, Tech, Math › Science Acid Definition and Examples Chemistry Glossary Definition of Acid Share Flipboard Email Print StanislavSalamanov / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 13, 2020 An acid is a chemical species that donates protons or hydrogen ions and/or accepts electrons. Most acids contain a hydrogen atom bonded that can release (dissociate) to yield a cation and an anion in water. The higher the concentration of hydrogen ions produced by an acid, the higher its acidity and the lower the pH of the solution. The word acid comes from the Latin words acidus or acere, which mean "sour," since one of the characteristics of acids in water is a sour taste (e.g., vinegar or lemon juice). This table offers an overview of the key properties of acids compared with bases. Summary of Acid and Base Properties Property Acid Base pH less than 7 greater than 7 litmus paper blue to red doesn't change litmus, but can return acid (red) paper back to blue taste sour (e.g., vinegar) bitter or soapy (e.g., baking soda) odor burning sensation often no odor (exception is ammonia) texture sticky slippery reactivity reacts with metals to produce hydrogen gas reacts with several fats and oils Arrhenius, Brønsted-Lowry, and Lewis Acids There are different ways of defining acids. A person referring to "an acid" is usually referring to an Arrhenius or Brønsted-Lowry acid. A Lewis acid is typically called a "Lewis acid." The reason for the differing definitions is that these different acids don't include the same set of molecules: Arrhenius Acid: By this definition, an acid is a substance that increases the concentration of hydronium ions (H3O+) when added to water. You might also consider increasing the concentration of hydrogen ion (H+) as an alternative.Brønsted-Lowry Acid: By this definition, an acid is a material capable of acting as a proton donor. This is a less restrictive definition because solvents besides water are not excluded. Essentially, any compound that can be deprotonated is a Brønsted-Lowry acid, including typical acids, plus amines, and alcohol. This is the most widely used definition of an acid.Lewis Acid: A Lewis acid is a compound that can accept an electron pair to form a covalent bond. By this definition, some compounds that don't contain hydrogen qualify as acids, including aluminum trichloride and boron trifluoride. Acid Examples These are examples of types of acids and specific acids: Arrhenius acidMonoprotic acidLewis acidHydrochloric acidSulfuric acidHydrofluoric acidAcetic acidStomach acid (which contains hydrochloric acid)Vinegar (which contains acetic acid)Citric acid (found in citrus fruits) Strong and Weak Acids Acids may be identified as either strong or weak based on how completely they dissociate into their ions in water. A strong acid, such as hydrochloric acid, completely dissociates into its ions in water. A weak acid only partly dissociates into its ions, so the solution contains water, ions, and the acid (e.g., acetic acid). Learn More Names of 10 Acids Do You Add Acid to Water or Water to Acid? Intro to Acids, Bases, and pH Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "Acid Definition and Examples." ThoughtCo, Aug. 29, 2020, thoughtco.com/definition-of-acid-and-examples-604358. Helmenstine, Anne Marie, Ph.D. (2020, August 29). Acid Definition and Examples. Retrieved from https://www.thoughtco.com/definition-of-acid-and-examples-604358 Helmenstine, Anne Marie, Ph.D. "Acid Definition and Examples." ThoughtCo. https://www.thoughtco.com/definition-of-acid-and-examples-604358 (accessed October 22, 2021). copy citation Watch Now: What are the Differences Between Acids and Bases? List of the Strong Acids and Key Facts Arrhenius Acid Definition and Examples List of Strong and Weak Acids Base Definition in Chemistry How to Calculate the pH of a Weak Acid Chemistry Vocabulary Terms You Should Know Names of 10 Common Acids What Is Glacial Acetic Acid? A to Z Chemistry Dictionary Bronsted Lowry Theory of Acids and Bases Is Negative pH Possible? Bronsted-Lowry Acid Definition Mineral Acid Definition and List pH Definition and Equation in Chemistry Neutralization Definition in Chemistry What Are Acids and Bases?