We come across acids in everyday of our lives, whether at home or in a chemistry laboratory performing chemical reactions, but not all of us are well-rounded with the key differences between the organic acids and the inorganic acids. There are characteristics and properties that distinguish organic from inorganic acids, and this article highlights them. We will first discuss each acid category and then highlight the main differences. The table at the end will wrap up the key differences.
What is an acid?
For many years, scientists have had different ways of defining acids, but they were reaching a common understanding of what really an acid is. Some of these definitions stated an acid as the proton donor, electron acceptor, hydronium ion donor, etc. Today’s common understanding is that an acid is a proton donor. When an acid reacts with bases, it yields water, and when it reacts with metal it expedites corrosion by forming hydrogen gas. At home, we come across the citric acid and acetic acid as the common acids found in our juices and vinegar, respectively. The characteristic taste of acids is sour.
Acids are typically categorized into inorganic and organic acids, and each category can also be categorized into strong and weak acids. In general, the pH level and the litmus test are used to identify the acid strength and identity, respectively. A pH between 1 and 7 indicates acidity. The lower pH indicates a strong acid, and a higher pH, say 6, indicates a weak acid. The identity of an acid is seen by the change of blue litmus to a red color. In solutions, a strong acid dissociates and ionizes completely, whereas a weak acid dissociate partially, and it donates fewer protons.
At room temperature, acids are liquids and are corrosive. As already indicated, they are categorized into organic and inorganic compounds. The key difference between these categories is that, organic acids are organic compounds that possess acidic properties and are typically weaker than the inorganic acids, whereas the inorganic acids, often interchangeably called mineral acids, are inorganic compounds with acidic properties and are typically stronger than the organic acids.
Because they are organic compounds that possess the acidic properties, they are therefore characterized by the inclusion of carbon in their structural and chemical properties as well as the hydrogen atoms. The common organic acids include lactic acid, carboxylic acid, citric acid, formic acid and acetic acid. They are characterized by the –COOH group in their structural properties. Even the compounds that have the –OH groups can have acidic properties, too. For example, the alcohols have the properties of an acid.
The organic acids can be further characterized into strong and weak acids. The weak acids dissociate partially in water and exist in equilibrium with the H+ ions and the conjugate base. Strong acids do not exist in equilibrium because they ionize completely in solutions. But, typically, the organic acids dissolve poorly in water, and dissolve perfectly in organic solvents. This is yet another key difference between them and the inorganic acid. Usually, the stability of the ion yielded after the acid dissociates determines whether it is a weak or strong acid.
As aforementioned, they are interchangeably called mineral acids because of their origin from mineral resources. They are essentially the inorganic compounds that have strong acidic properties. The common acids that you have probably come across include HCL, H2SO4, HNO3, as strong acids and H2S, HF, HNO2, and HCN. This degree of acidity can also be seen from the pH levels. Typically between 3 and 6 pH levels lies weak acids, and below 3 lies the strong acids. They dissolve well in water, with the weak acids dissolving partially.
A clear distinction between the inorganic acids and the organic acids is seen in the absence of carbon atoms in most of them. Some such as sulfuric acid contain the oxygen atoms. They have different structural properties, but the hydrogen atom is synonymous with them, as evident in the above inorganic acids. This justifies the definition that acids donate hydrogen atoms in aqueous solutions and also accept electrons from electron-rich compounds. The equation below demonstrates the typical reaction of acids in water.
HCL + H2O → CL– + H3O+
That is how the inorganic acid dissociates into Hydronium ions regardless of the chemical structure of the acid. The equation gives the identity of the acid. The definition that says the difference between organic and inorganic acid is the carbon items is not generally accurate, because some inorganic acids such as HCN contain the carbon atom in them.
Difference between inorganic and organic acid
- Organic acids are organic compounds that have acidic properties whereas the inorganic acids are the inorganic compounds that possess acidic properties
- All organic acids contain the carbon atoms whereas not all inorganic acids do
- Organic acids are generally weaker in strength whereas the inorganic acids are stronger
- Inorganic acids are heavily corrosive and reactive with metals than the organic acids
- Organic acids have a biological origin whereas the inorganic acids originate from minerals
- Organic acids are highly soluble in organic solvents whereas the inorganic acids are not
- Organic acids dissolves poorly in water whereas inorganic acids dissolves well
The table below further gives a succinct glimpse of the difference between organic and inorganic acids.
|Are organic compounds
|Are inorganic compounds
|All contain carbon atoms
|A few such as HCN contain carbon atoms
|Generally weak acids
|Generally strong acids
|Dissolve poorly in water
|Dissolve well in water
|Dissolve well in organic solvents
|Dissolve poorly in organic solvents
In a nutshell, organic acids and the inorganic acids differ in chemical and structural properties. They are both capable of neutralizing the base, accepting electrons from electron-rich compounds and donating the H+ ions. When reacting in an aqueous solution, they are both capable of yielding the hydronium ions. Their pH ranges from 1 to 7, with 1 being the strongest and 7 being the weakest. Their identity is seen when they turn blue litmus to red. These show their many common properties.
From our analysis, we saw the key difference between these two categories of acids. The organic acids, the likes of acetic and carboxylic acid, are essentially weaker counterparts, whereas the inorganic acids, the likes of HCL and H2SO4, are stronger acids. Even the weak inorganic acids are typically stronger than the organic acids.
In terms of structural properties, the organic acids are usually identified with the –COOH or even the –OH group. Carboxylic acid structure, for example, can be written as RCOOH. Because they are organic compounds with acidic properties, the carbon atoms give identity to the organic acids. HCN cannot be regarded as organic acid because of the weaker hydrogen and carbon atom. 
Author: Lusi Madisha
Lusi is a professional writer and a researcher for more than seven years. She is a chemical engineering graduate from the University of South Africa.