Strong Acids: List Of Top 7 Strong Acids 

Any young learner who has chemistry as a subject in school knows how important it is to know and learn about acids and bases. Today’s blog post focuses on a crucial part of – strong acids. Do you often find yourself clueless when someone asks you what the strong acids are? If yes, you are in luck. Read ahead and find out what strong acids are the seven important strong acids, their significance, why you should be careful while using them in the lab, and more. 

Let the scrolling begin. 

What Are the Strong Acids? 

Before leading you to the list of strong acids, you must know what strong acids are. In the dialect of chemistry, any acid labeled as a strong acid isn’t necessarily too powerful or corrosive. Instead, the factor that decides the classification of strong acids is their ability to release hydrogen ions (H+) into a given solution. 

When you mix a strong acid with water (H2O), it will completely dissociate into ionic form – H+ and an anion. Strong acid molecules break up in a solution if said in an even easier way. Any acid that cannot do so falls under the weak acids list. These weak acids dissociate less than 1% in solution forms. 

When the weak acids are dissolved in water, all their molecules do not break up completely. Only 1% of their molecules break up to release a hydrogen ion. Thus, you can conclude your answer to what are the strong acids by saying that these are those seven acids that completely dissociate into ions on dissolution with water. Any acid that doesn’t do so is not a strong acid. 

Dissociation of Strong Acids and Weak Acids 

The dissociation of strong acids, when dissolved in water, has to do with a chemical reaction. For instance, when you look at the ionization reaction of hydrochloric acid (HCl), one of the seven acids in the strong acids list, it is as follows: 

HCl → H+ + Cl- 

In the reaction, you can see hydrogen ion H+ and anion Cl- are the end products. It means that HCl completely ionizes during the reaction. Another importance of this dissociation is that it only proceeds in one direction. It concludes that once you ionize a strong acid, the reaction will stop there. Also, any such reaction is irreversible. 

Now, let us look at a similar reaction of ethanoic acid, a weak acid. It is as follows: 

CH3COOH + H2O  H3O+ + CH3COO- 

In the above equation, you can notice that the arrow points in both directions, unlike the reaction of strong acid HCl. It means that this reaction can proceed forwards and backward. It is a reversible reaction. This is not the case for strong acids. In their case, dissociation that once takes place cannot be reversed. 

Thus, those acids that only slightly disassociate (weak acids) reform multiple times. Their hydrogen ions keep moving and may once be a part of water and, in the next, an amount of the acid. This kind of reversible reaction is not possible in the case of strong acids, which makes strong acids important for chemical equations. It is therefore crucial for students to memorize these acids.  

List of strong acids 

Students can easily learn their names because there are only seven common strong acids. All other acids that are not a part of the list of strong acids form weak acids. Here is a glance at all the 7 strong acids and their chemical formulae: 

  1. Chloric acid: HClO3
  2. Hydrobromic acid: HBr 
  3. Hydrochloric acid: HCl 
  4. Hydroiodic acid: HI 
  5. Nitric acid: HNO3 
  6. Perchloric acid: HClO4 
  7. Sulfuric acid: H2SO4 

With the above list, now you can easily answer questions like: is H2SO4 a strong acid 

A Closer Look at The Seven Strong Acids 

So, all the seven acids in the strong acids list dissociate completely into their ions in solutions. They thus can yield one or more protons (H+ cations) per molecule. Now, let us talk about all these acids a bit more. 

Chloric Acid (HClO3) 

The chemical compound is an oxoacid of chlorine and has the chemical formula HClO3 is chloric acid. This chlorine oxoacid is popular as a powerful oxidizing agent and highly acidic in nature. When it comes to the molar mass of HClO3, it is calculated to be 84.45 grams per mole. Another crucial thing students must know about chloric acid is that it is considered to be thermodynamically unstable. 

The reason behind it is that this chemical compound can readily undergo disproportionation. Under normal conditions, this acid simultaneously oxidizes and reduces to give two different end products (H+ and an anion). However, there is a way to make this acid more stable. This can happen in relatively cold environments or when you place it in an aqueous solution that has a concentration of no more than 30%. 

Points To Remember: 

  • Its chemical formula is HClO3. 
  • It has a molar mass of 84.45 grams per mole. 
  • It is thermodynamically unstable under normal conditions. 
  • It is considered stable in cold environments/ 30% aqueous solution 

Hydrobromic Acid (HBr) 

The acid that is formed when hydrogen bromide (a diatomic molecule) is dissolved in water is Hydrobromic acid. This solid acid has an acid dissociation constant pKa −9 and is represented by HBr chemical formula. When compared to other acids in the list – hydrochloric acid and hydroiodic acid, here is what you can observe. 

HBr is stronger than the former. However, acidic strength is similar to that of the latter. The acid is also popular as one of the most potent known mineral acids. Further, it is chiefly used for the making of various inorganic bromides. Some of them include sodium bromides, zinc bromides, and calcium bromides. 

While HBr is an excellent Organobromine compound processing reagent, it can also do more. This strong acid can cleave several ethers. Another thing students must note is that acid plays a part in extracting ores. This is via the alkylation reactions that are a major part of the ore extraction process. 

Points To Remember: 

  • Its chemical formula is HBr. 
  • Its acid dissociation constant (pKa) is of magnitude −9. 
  • It is a very solid acid. 
  • It is a much stronger acid than hydrochloric acid. 
  • It has the same acidic strength as hydroiodic acid. 
  • This acid is one of the most potent known mineral acids. 
  • It is an effective reagent for the processing of Organobromine compounds. 
  • It can also cleave several ethers. 
  • It can catalyze various alkylation reactions for the extraction of ores. 

Hydrochloric Acid (HCl) 

The colorless acid that is also identified as muriatic acid and goes by HCl chemical formula is hydrochloric acid. This inorganic acid is highly acidic and has a very pungent odor. It should be handled with care as it can damage the skin on contact. This corrosive acid further has the simplest acidic system (contains chlorine and water). It is nothing but a solution of hydrogen chloride in water. 

The chemical compounds in this system include the chloride ion and the hydronium ion. Further, this is one of those acids that are of major importance in biology too. HCl is a natural component of gastric acid (the acid formed naturally in the digestive tracts of almost all animals). In fact, even the human digestive system produces it naturally as it aids in the digestion of food. 

Points To Remember: 

  • Its chemical formula is HCl. 
  • It is also identified as muriatic acid. 
  • It is a colorless inorganic compound. 
  • It has a very pungent odor. 
  • It is highly acidic in nature. 
  • Its direct contact can cause damage to the skin. 
  • It is a natural component of gastric acid in animals. 
  • It is produced in the human digestive system naturally. 

Hydroiodic Acid (HI) 

Hydroiodic acid, or as some call it, hydriodic acid, is the second strongest acid of hydrogen and a halogen after hydrostatic acid. It is represented by the formula HI. This extremely acidic solution of hydrogen iodide and water is a widely used chemical reagent. Also, when placed in an aqueous solution, it ionizes completely. 

While HBr is a solid acid, this one exists as a colorless liquid under standard temperature and pressure conditions. This acid is known to have a slightly acrid odor in this state. Further, it has a boiling point of 400 K (127 degrees Celsius) and has a density of nearly 1.7 grams per milliliter under these conditions.  

Points To Remember: 

  • Its chemical formula is HI. 
  • It is also known as hydriodic acid. 
  • It is the second strongest acid of hydrogen and a halogen. 
  • Under standard conditions STP), it is a colorless liquid. 
  • It has a slightly acidic odor. 
  • It has a density of 1.7 grams per milliliter. 
  • It has a boiling point of 127 degrees Celsius (400 Kelvin). 

Nitric Acid (HNO3) 

The next strong acid is represented by the chemical formula HNO3 and is often called aqua fortis or the spirit of niter. This tremendously corrosive mineral acid has a molar mass of 63.01 grams per mole. It is widely used in nitration reactions as it is a powerful oxidizing agent. The acid, thus, makes the addition of a nitro group to a given reactant much easier. 

Further, it exists in liquid form under standard conditions for temperature and pressure (STP) and has a melting point of 231 Kelvin. The boiling point of the acid, on the other hand, is 394 Kelvin. Besides this, it may be colorless, yellowish-red, or yellow in color under STP. Also, it has an extremely suffocating and acrid odor in the state. 

Points To Remember: 

  • Its chemical formula is HNO3. 
  • It is also known as the spirit of niter/aqua fortis. 
  • It is a corrosive mineral acid. 
  • It is a powerful oxidizing agent. 
  • Its molar mass is 63.01 grams per mole. 
  • Under STP, it exists as a colorless, yellowish-red, or yellow liquid. 
  • It has an extremely suffocating, acrid odor. 
  • It has a melting point of 231 Kelvin. 
  • It has a boiling point of 394 Kelvin. 

Perchloric Acid (HClO4) 

The chemical formula HClO4 represents the next acid in the list of strong acids. This colorless mineral acid is very powerful and is used in its aqueous solution. Compared with sulfuric acid and nitric acid, it is a stronger acid than them. While it is used in the liquid form to a great extent, it acts as a potent oxidizer in its dry form. 

Due to the powerful oxidizing properties of this acid, it has numerous stringent regulations that you must follow while handling it. This can especially be true when the acid is used in contact with metals like aluminum (Al), organic matter like wood, and certain kinds of plastics. It is because the acid is highly reactive in its presence. In fact, any research on this strong acid needs to be performed with the help of fume hoods. 

Points To Remember: 

  • Its chemical formula is HClO4. 
  • It is a very strong mineral acid. 
  • It is a colorless acid. 
  • It is stronger than sulfuric acid and nitric acid. 
  • It is a very potent oxidizer in dry form. 
  • It is highly reactive for metals and organic matter. 

Sulfuric Acid (H2SO4) 

The last and the seventh acid in the list of strong acids, represented by H2SO4, is sulfuric acid. It can also be spelled as “Sulphuric” and is commonly known as vitriol oil or oil of vitriol. This mineral acid is colorless, odorless, and comprises Oxygen (O), Sulphur (S), and Hydrogen (H). It is, further, highly viscous in nature and is water-soluble. The acid can be synthesized in a highly exothermic reaction (for which ΔH⚬ is negative). 

Due to the strong acidic nature and oxidizing properties of the chemical compound, it is highly corrosive. It is very dangerous and can cause serious chemical burns on contact even at low concentrations. At high concentrations, the acid can even cause secondary thermal burns. Another thing you must know is that this strong acid is hygroscopic in nature. It even can absorb water vapors from the air readily. 

Points To Remember: 

  • Its chemical formula is H2SO4. 
  • It is also known as vitriol oil or oil of vitriol. 
  • The mineral acid is colorless and odorless.
  • It is highly viscous in nature. 
  • It is water-soluble and hygroscopic. 
  • It is well-known for its oxidizing properties. 
  • It has a very strong acidic nature. 
  • It is dangerous even at lower concentrations. 

Are There Any Other Strong Acids? 

Apart from the seven acids in the list of strong acids, there is no other strong acid that can occur in an everyday situation. However, some acids are produced industrially. Two examples of these acids are: 

Triflic acid/Trifluoromethanesulfonic acid (H[CF3SO3]) 

This sulfonic acid is colorless and a slightly viscous liquid. It is hygroscopic in nature and is soluble in polar solvents. The acid is mainly used in research for esterification as a catalyst. 

Fluoroantimonic acid (HSbF6]) 

Depending on its ingredients, this superacid is over a billion times stronger than even 100% pure sulfuric acid. It is a colorless liquid with a molar mass of 236.76 grams per mole. 

Are Strong Acids Always Strong? 

No, a strong acid may not always be strong. It all depends on their concentration. Typically, the more concentrated strong acids become, the less they can dissociate. When they cannot fully dissociate, they are not as strong. Usually, a strong acid can be fully (100%) dissociated in solutions that have a concentration of 1.0 M or lower. 

Are There Any Weak Acids? 

Almost all those acids that are not a part of the strong acids list can be classified as weak acids. These acids cannot completely dissociate into their ions when mixed with water. For instance, if you mix HF with water, it will dissociate H+ and F- ions. However, if some HF ions remain in the solution, the acid is not a strong acid. 

Since there are only seven major strong acids, the weak acids list is far longer than the list of strong acids. Typically, most organic acids come under the category of weak acids. Below, you can find a list of some of the weak acids that you must know about: 

  • Oxalic Acid (HO2C2O2H) 
  • Sulfurous Acid (H2SO3) 
  • Hydrogen Sulfate Ion (HSO4 -) 
  • Phosphoric Acid (H3PO4 -) 
  • Nitrous Acid (HNO2 -) 
  • Hydrofluoric Acid (HF) 
  • Methanoic Acid (HCO2H) 
  • Benzoic Acid (C6H5COOH) 
  • Acetic Acid (CH3COOH) 
  • Formic Acid (HCOOH) 

All the above weak acids are ordered from strongest to weakest. Now, let us give you a brief idea of why these acids are weak. For it, let us look at the dissociation of ethanoic acid in water: 

CH3COOH + H2O  H3O+ + CH3COO- 

Ethanoic Acid + Water  Hydronium Cations + Ethanoate Anions 

In the above equation, you can see that ethanoic acid, when mixed with water, produces hydronium cations and ethanoate anions. However, the reaction arrow () points towards both directions. It shows that only about 1% of ethanoic acid converts to ions. The rest of the acid remains the same. 

Also, since this reaction operates in both directions and the back reaction is more favorable than the forward one, ions can readily change back to the acid once formed. (In the case of strong acids, the forward reaction is clear, and there is no back reaction.) Since these ions go back and forth between acid and water, it makes the acid a weak acid. 

To Conclude With

Strong acids consist of seven main acids – chloric acid, hydrobromic acid, hydrochloric acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid. These can completely dissociate in water, giving them the title of strong acid. 

Please note that the term strong has nothing to do with its acidic strength. It is different for each of them. In fact, even a strong acid can be safe to use when handled with care and at a particular concentration. On the other hand, some weak acids (they dissociate only a small amount) can be highly corrosive and dangerous to work with without precautions.