In common parlance, an acid is any compound which tastes sour, turns blue litmus paper red, reacts with metallic and carbonate compounds and scores less than 7 on a pH value scale. Acids may be found in solid, liquid as well as gaseous forms, depending upon the temperature in which they are found. They may either occur in pure, undiluted form or as solutions. Properties of bases (alkali) and acids differ radically and these two compounds are diagonally different from each other with regards to their reactions to similar substances. Before we jump to the physical and chemical properties of elements and compounds that we identify as acids, let us first take a look at some popular definitions and concepts on what acids are.
Definitions and Concepts of Acid
Below are three modern-day definitions of acids which have been arrived at by three prominent chemists who based their definitions on certain individual concepts. Each of these concepts is founded upon a separate aspect of the subjective substance's chemical reaction with other elements. Let us take a look at these definitions, concepts and their limitations.
|Arrhenius Acids||Svante Arrhenius||A substance which increases the concentration of hydronium ion H3O+ when it is dissolved in water is an Arrhenius acid.||Equilibrium disassociation of water into hydroxide and hydronium ions.||Failure to recognize transfer of proton involved in acid-base reactions.|
|Brønsted-Lowry Acids||Johannes Nicholaus Brønsted & Thomas Martin Lowry||Any substance that gives a proton away to a Brønsted-Lowry base is a Brønsted-Lowry acid.||Transfer of proton from acid to base.||Failure to recognize electron pair acceptance.|
|Lewis Acids||Gilbert Lewis||A substance that accepts a couple of electrons from another substance is a Lewis acid.||Inclusion of those acid base reactions which do not involve proton transfer.||Unless specifically expressed, all acid-base reactions are assumed to rely upon the transfer of a proton from acid to base, thereby, rendering the Brønsted-Lowry definition more popular.|
General Properties of Acids
The physical and chemical properties of bases and acids is what differentiates them. Let us take a brief look at the various properties of acids to identify those traits which make acids what they are.
- Acids and acidic compounds taste sour and give off an acrid odor. Take, for instance, vinegar. You can smell the stinging sour odor as soon as you open a bottle of vinegar and we all know how vinegar tastes!
- All acids and acidic compounds react with metals and such reaction always results in the production of hydrogen.
- Acids are good conductors of electricity and are so corrosive that they tend to eat away at most things which come in contact with them.
- Some acids give away one proton each molecule during dissociative processes and such acids are called Monoprotic acids.
- Some acids lend more than one protons per molecule during disassociations and such acids are called Polyprotic Acids.
- One of the most remarkable chemical properties of acids and bases is that they react with each other to produce salts. This process is known as neutralization. For instance, hydrochloric acid would react with sodium hydroxide to produce salt (sodium chloride) and water!
- Acids are soluble in water and an acid can be either a strong acid or a weak acid. A strong acid is that which ionizes completely in a water solvent solution by the renunciation of one proton. Sulfuric acid, hydrobromic acid and hydrochloric acid are prominent examples of strong acid. Sulfuric acid uses range from their use in car batteries, fertilizers and as industrial catalysts. Hydrochloric acid in stomach manifests as gastric acids. A weak acid is that which ionizes incompletely and does not release all the hydrogen it contains. It lends only some amounts of its proton to an aqueous solution. Good examples of weak acid are acetic acid and boric acid. Phosphoric acid is also a weak acid and phosphoric acid uses include rust removal, acidifying food and beverages and as a pH adjuster in several cosmetics, among others.
That was a brief overview regarding acid properties. Acids, bases and their properties are a large domain of chemistry and there is much more detail involved that is provided here. This article is an attempt to provide a brief glance at the most striking and distinctive properties of acids. Hope this helps budding science scholars and gives an idea of how acids behave!