Acids and Bases
People are unaware of how smart early humans were. We always consider newer generations superior to those that came before. However, we underestimate past generations and are unable to see the complete picture.
Many ordinary and extraordinary discoveries were made over the course of history. As tribes crossed paths, they learned and discovered many new things from each other. Things that were abnormal and weird soon became everyday objects.
One of the examples is acids and bases. These were discovered by the ancient Greeks. The Greeks tried to organize these varied substances and scientifically tested them in many ways to distinguish them. They tried testing them on taste, and they sorted the substances into categories: sour, bitter, sweet or salty. As the Greeks influence started to wane, they started referring to sour substances like lemon juice and vinegar as acid. The words acid and acidic both originate from the Latin word for sour taste.
Although Bases were not well studied, they were believed to neutralize acids. This was consistent with their beliefs in balance and harmony in nature. At that time, bases were referred to as alkalis–a word derived from the Arabic word for roasting. It is still unclear why alkalis were later called bases.
During and after the renaissance, alchemists started understanding better the properties of acids. They discovered that the stronger they made the solutions the more corrosive it became. It would eat through things like metal and certain types of rock. The alchemists started to develop acids with different strengths, such as Sodium Carbonate ( baking soda), Acetic Acid, Citric Acid, and Hydrochloric Acid.
In 1300, a Spanish scholar decided to use litmus for studying acid and bases. He was the first person known to use litmus to test acidity. This idea was further explored by Robert Boyle, who found some plant substances changed colours in the vicinity of acids and bases. One of these was syrup of violets (flowers) which turned bases blue and acids red. This opened up many new possibilities for chemists. They could work out the proportions of acids and bases that could neutralize each other, allowing them to test their strengths.
During the 18th century, an idea was formed. It was assumed that heat was an element contained within metals that could explode. George Ernst Stahl gave the idea of acids being extracted from Sulphur and their strength was ordained from phlogiston, though this assumed fact would be proven a fiction by the end of the century.
Antoine Lavoisier was the first one to look at it from a different perspective. Though later proven wrong, he proposed oxygen was responsible for making acid. These observations led to further studies. Humphrey Davey, known for his studies in gases, proved him wrong. He found that not all acids contained oxygen.
Today, there are three main theories that are widely accepted: the Arrhenius theory, the Bronsted Lowrey theory and the Lewis theory.
Svante Arrhenius, a Swedish chemist, proposed that acids and bases gained properties from the actions of ions in aqueous solution. His solution was widely accepted, earning him a Nobel Prize award in 1903. The Arrhenius theory suggests that when dissolved in water, acid increases the concentration of H+ ions in it. One of the benefits of this theory is that it explains how the reaction between acids and bases yields salts and water. An important limitation of the Arrhenius’ definitions of acids and bases is that it fails to explain how substances lacking hydrogen or hydroxyl groups are acidic or basic in nature.
In 1909 a scientist known as Soren Soren invented the pH scale, this later was known as one of the most trusted ways to measure a substance’s acidity or basicity. pH stands for ‘potential of hydrogen’. A pH can vary from a value of 0 – 14, where 0 is the most acidic and 14 is the most basic a substance can be. For example, Acids can have a pH anywhere from 0 – 7, while bases can have a pH anywhere from 7-14.
In 1923 the scientist duo Johanuss Nicolaus Bronsted and Thomas Martin Lowery created the Bronsted-Lowrey theory. This theory suggests an acid as a donor of protons and a base is defined as an acceptor of protons and thus an acid increase the concentration of H+ ions in the solution. On the other hand, the bases accept protons from water to yield hydroxide ions. This theory has the ability to explain the acidic or basic nature of ions.
In the same year, the scientist Gilbert S Lewis had a theory too, his theory proposed that the substance that accepts a pair of electrons to form a covalent bond is an acid. The base is a substance that donates a pair of electrons to form a covalent bond. So, an acid-base reaction is represented by the transfer of a pair of electrons from a base to an acid. All of these theories suggest various things, all of them are right in their own ways. But the easiest way to explain what an acid is that it is any hydrogen-containing substance that can donate a proton (a hydrogen ion) to another substance. A base is an ion able to accept a proton from an acid.
It took many centuries for us to reach our level of understanding, and there is much that yet remains to be explored about acids and bases. It was a culmination of the work started all those centuries ago, that helped us discover a concept so fundamental to modern chemistry.