What is Acid in Chemistry? - Definition & Overview

Lesson Transcript
Instructor: John Williams
Acid, in chemistry, refers to the chemical agents that discharge hydrogen ions when added to water. Learn an overview of how acids work, their characteristics, definitions of weak acids and strong acids, and the different types of acids in the human body. Updated: 09/23/2021

Introduction to Acids

So many of us have heard of the term pH, which in general is the measure of the amount of acidity or alkalinity that is in a solution. More specifically, it is a measure of the amount of protons or hydrogen ions that are present in an aqueous solution. Acids are primary contributors to the measure of pH in a solution, and the presence of acids a key characteristic of almost all solutions, from blood in the body to foods and drinks we consume. Let's discuss what an acid is and how it affects the pH of solutions when added.

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  • 0:00 Introduction to Acids
  • 0:34 How Acids Work
  • 1:18 Weak vs. Strong Acids
  • 2:32 Acids and the Human Body
  • 3:00 Other Common Characteristics
  • 3:18 Lesson Summary
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How Acids Work

The pH scale is a scale that is used to represent the level of acidity in a solution. A solution with a pH of 7 is neutral, while a solution with a pH below 7 is an acid, and a solution with a pH above 7 is a base. An acid dissociates, or breaks apart, and donates protons, or hydrogen ions, in an aqueous solution, while a base donates hydroxide ions in a solution. Water, for example, is neutral with a pH of 7. When acids are added, they release more hydrogen ions into the solution, and this causes the pH of the solution to drop. Let me repeat: more hydrogen ions equals a lower pH and a more acidic solution.

An Acid Releases Hydrogen Ions in Solution
example of acid

Weak vs. Strong Acids

All acids will release hydrogen ions into solutions. The amount of ions that get released per molecule will determine if the acid is weak or strong. Weak acids are acids that partially release the hydrogen atoms that are attached. These acids, then, may lower pH by dissociation of hydrogen ions, but not completely. Weak acids include acetic acid, which is vinegar, and citric acid found in oranges and lemons.

Strong acids, on the other hand, completely dissociate and release ALL of their hydrogen atoms. This means that strong acids, in general, are more potent in lowering the pH of a solution. There are only 7 strong acids, including hydrochloric acid, which can be found in the stomach, and sulfuric acid, a corrosive acid found in things such as car batteries and fertilizers.

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