Acid is a substance that contains hydrogen and can donate a proton (hydrogen ion) to another substance. So, how strong an acid depends on its ability to release hydrogen ions (H+) into a given solution. So, the acids that completely dissociate into their ions (H+ and an anion) when they are mixed with water are referred to as strong acids. The other acids that do not tend to dissociate completely when mixed in water are known as weak acids.
Strong acids are not more in number. The seven most-common strong acids are described below:
1. Hydrochloric Acid
It is also known as muriatic acid. It is an inorganic molecule with the chemical formula HCl. It is colorless and smells pungent. HCl is secreted by humans and most animals in their stomachs to help in the digestion of food. It is a natural component of gastric acid formed in the digestive tract of humans and most animals.
It has a diatomic molecule wherein hydrogen and chlorine atoms are bonded with each other through a single covalent bond.
It has lots of commercial uses; it is required in the production of inorganic compounds, refine metals, pickle steel and to regulating pH. Despite being a strong acid, it is less hazardous to handle. Further, it is less expensive and is easy to store.
2. Nitric Acid
Nitric acid is an inorganic acid, which also goes by the names aqua fortis and the spirit of niter. Its chemical formula is HNO3 and is highly corrosive and toxic in nature. It is colorless when it is pure but gradually turns yellow over time due to its decomposition into nitrogen oxides and water.
It is widely used for nitration wherein a nitro group gets added to a molecule. It is also used as an oxidant in the production of nylon and as an oxidizer in rocket fuel. The other major use of nitrogen is in the preparation of fertilizers such as ammonium nitrate, and explosives such as trinitrotoluene (TNT).
3. Sulphuric Acid
It also goes by the name oil of vitriol. Its chemical formula is H2SO4. It is colorless, viscous and also does not have any odor. It attracts water vapor strongly so it is not found in pure form naturally. In other words, it is highly soluble in water and is a component of acid rain. It is formed naturally through the oxidation of sulphide mineral present in the rocks.
It is a strong acid so it should be handled with care. It tends to dehydrate skin upon contact. It is mainly used in the production of fertilizers. It produces phosphoric acid which produces phosphate fertilizers. Besides this, it is also used in the production of dyes, resins, detergents, paper, explosives, drugs, batteries, and in the treatment of water.
4. Hydrobromic Acid
Hydrobromic acid is formed when hydrogen bromide is dissolved in water. Its chemical formula is HBr. In solid state, its dissociation constant is pKa -9 and its molecular mass is 80.9 g/mol.
As its chemical formula suggests, it is a diatomic molecule wherein a hydrogen atom is bonded to a bromine atom through a covalent bond. Its physical properties like boiling point, melting point, etc., depends on its concentration in the given solution.
Hydrogen bromide is a strong acid. It is colorless gas, which is suffocating. It is also highly corrosive so can cause burns when comes in contact with skin. It is widely used in the formation of many inorganic bromides and organobromine compounds like zinc bromide, allyl bromide, etc.
5. Hydroiodic Acid
It is an aqueous solution of hydrogen iodide. Its chemical formula is HI. Being a strong acid, it dissociates completely in an aqueous solution. It reacts with atmospheric oxygen to form iodine.
4 HI + O2 → 2H2O + 2I2
In its anhydrous form, its molecule is made of one atom of an iodine atom and one atom of a hydrogen atom. It is colorless and has an acrid odour. Commercially, it is prepared by the reaction of iodine with hydrazine which results in the formation of nitrogen gas and hydrogen iodide.
It is mainly used to form alkyl iodides (organic compounds) when it is reacted with alkenes or primary alcohols. Further, it acts as a reducing agent in various industrial processes.
The Hydroiodic gas is toxic, so when inhaled it may cause irritation to the eyes, skin, and the mucous membrane. This acid burns the skin and damages the eyes. Further, long-term exposure to its low concentrations can also be harmful.
6. Perchloric Acid
It is an inorganic acid, which is very strong and is used as its aqueous solution. Its chemical formula is HClO4. It also goes by names hyperchloric acid (HClO4) or hydroxidotrioxidochlorine. It appears as a colorless and odorless solution when its concentration is 50% to 72%. A container of perchloric acid when exposed to heat for a longer duration can rupture violently.
Its molecular weight is 100.46 g/mol, density is 1.768 g/cm3, melting point is 17 degrees Celsius, and boiling point is 203 degrees Celsius. It is used as an oxidizer to separate sodium from potassium. It is also used in explosives, rocket fuel, plating metals, and more.
The traditional method of preparing Perchloric acid involves the reaction of sodium perchlorate (NaClO4) with HCl to form perchloric acid as shown below:
NaClO4 + HCl → NaCl + HClO4
It is a strong acid so if it is inhaled accidentally it can cause a burning sensation in the nose and throat. Further, long-term exposure may cause vomiting. Also, when it is heated, it produces toxic gases.
7. Chloric Acid
It is an oxoacid of chlorine with the chemical formula HClO3. It is highly acidic and a strong oxidizing agent. Its molecular mass is 84.45 grams per mole. This acid is considered thermodynamically unstable as it easily undergoes disproportionation. It shows under normal conditions, it undergoes oxidation and reduction simultaneously to give two different products: H+ and an anion. To increase the stability of this acid, the environment should be cold or its concentration in an aqueous solution should not be more than 30%.