10 Facts on Acids

By Philip McIntosh
Published: December 27, 2016 | Last updated: April 21, 2021 05:15:35

Key Takeaways

Acid rain. Acid fast. Acid test. Okay, so what exactly is an acid?

Acid rain. Acid fast. Acid test. Okay, so what exactly is an acid?
In the simplest sense, an acid is a substance that ionizes to generate hydronium ions (H+ cations) when dissolved in water. This is known as the Arrhenius definition. It’s not scientifically very useful, but for practical understanding it is often enough.
An acid can also be understood as a substance that donates a proton (an H+ ion). That is part of the Brønsted-Lowry definition.
Acids exist in a balance of some kind with their chemically opposite entities, the bases. Bases generate OH– anions readily when dissolved in water.
It is no accident that when H+ ions meet OH– ions, they react to form H₂O—water.
The acidity of a solution is described by its pH value. pH is a measure of the H+ and OH- concentrations in a solution.
When the number of H+ ions equals the number of OH– ions, water is formed, and there are few free H+ In this case the solution is neutral which is 7 on the pH scale. Solutions with pH values less than 7 are acidic.
A weak acid does not release all of its protons when dissolved. A strong acid ionizes completely to release all of its protons into solution.
The solubilities of many nutrient elements are pH sensitive, with acidic conditions required for good availability. This is why grow system pH values should be monitored and maintained in the 5.5-6 range for most applications.
What could be stronger than an acid? A superacid. Superacids have acidity greater than 100 per cent sulfuric acid and can be trillions of times stronger. The pH scale doesn’t properly work to describe a superacid.

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Written by Philip McIntosh | Science & Technology Writer, Teacher

Philip McIntosh is a science and technology writer with a bachelor’s degree in botany and chemistry and a master’s degree in biological science. During his graduate research, he used hydroponic techniques to grow axenic plants. He lives in Colorado Springs, Colorado, where he teaches mathematics.

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