HNO3 Is It A Strong Acid?

We would definitely pay more attention in class if we as students understood that everything we are, do, and see around us is a part of chemistry, rather than merely enduring the classes.

Have you ever wondered what makes a substance acidic?

As a result, an acid is a chemical that donates hydrogen ions. It usually has a pH of less than 7. Acids, on the other hand, are split into two types based on their reactivity: weak and strong.

We’re going to speak about nitric acid today (HNO3). Nitric acids (HNO3) were commonly utilised by alchemists as early as 721, without even knowing their chemical properties.

Is HNO3 a powerful acid, though? Yes, with a pH of 3.1, HNO3 is a strong acid. The ability of an acid to dissociate in water and form hydronium ions (H+ or H3O+) determines its strength. HNO3 acid dissociates fully into H+ and NO3- ions in an aqueous solution, making it a powerful acid. In water, strong acids always dissociate fully.

Following this comment, scientists discovered that HNO3 fully dissociates in water, allowing it to be classified as a strong acid, through several studies.

This chemical is highly corrosive and poisonous since it is a strong acid.

Why is HNO3 such a powerful acid?

Strong acids’ ability to entirely dissociate in water renders water acidic. But why does this happen in the first place? Why do strong acids like HNO3 totally dissolve whereas weak acids just partially dissolve?

This is due to a few chemical features of acids, such as polarity, bond strength, and conjugate base stability.

The level of dissociation of these components varies depending on the acid.

The polarity of the H-X bond is the first factor to consider.

Acids become more powerful as the polarity of their ions rises. The polarity of the ions increases as their electronegativity increases. As a result, the acid dissociates more easily in water.

The dissociation of HNO3 is depicted in the following equation.

——> HNO3 (aq) + H2O (l) ——> H3O+ (aq) + NO3- (aq)

H+ and anion bonding strength

The dissociation of an acid in water is inversely proportional to its bond strength. As a result, the weaker the binding strength, the more easily they can be separated into ions.

As a result of the weak link between the hydrogen ion and NO3, they rapidly separate. The length of this connection is determined by the size of the anion atom.

The link between NO3 and other anions is easily broken because NO3 is bigger than other anions.

The formation of a conjugate base

Conjugate bases are those that develop when the H+ ion is removed from a molecule. If the conjugate base is stable, the acid will dissolve more readily in water.

In other words, the conjugate base’s stability is exactly proportional to the acidity of the molecule.

The conjugate base in HNO3 is NO3-. It produces an acid that is fully insoluble in water due to its high stability.

What exactly is HNO3?

Nitric acid’s chemical name is HNO3. It was given the Latin name Aqua Fortis, which means “strong water.” Because the chemical properties of nitric acid were unknown in ancient times, it was assumed to be highly acidic.

Henry Cavendish, a British scientist, identified the chemical nature and content of the substance in 1784. Nitric acid is a colourless chemical that seems to be water to the human eye. However, since it decomposes into nitrogen oxides and water, it develops a yellowish hue over time.

Three oxygen atoms, one nitrogen atom, and a hydrogen atom make up the chemical nitric acid. One double bond and three single bonds connect these atoms.

The NO3- has a weak single bond with the hydrogen atom, which breaks rapidly when its aqueous solution reacts with water.

Individual charges in the nitric acid molecule can be out-posted by resonance since the net charge on the molecule is 0.

This is the subject of a separate article that I’ve published. Investigate the Lewis Structure of HNO3.

HNO3 Chemical Properties

HNO3 (nitric acid) is a highly reactive chemical. It has a wide range of acidic, nitrating, and oxidising characteristics.

If stored above 0 degrees Celsius, anhydrous nitric acid will decompose. When you start boiling it at room temperature in the presence of light, it starts to decompose.

It then decomposes, leaving nitrogen dioxide, water, and oxygen molecules behind.

——-> 4HNO3 + heat + light ——-> 2H2O + 4NO2 + O2 = 2H2O + 4NO2 + O2

Acidic Characteristics

Salts are formed when nitric acid reacts forcefully with alkalis, basic oxides, and carbonates. Strong nitric acid reacts with strong bases or basic oxides to produce this type of neutralisation reaction.

When nitric acid reacts with metals, its oxidising nature prevents it from contributing protons.

As a result, the salts that result have a higher oxidising state. This chemical reaction is particularly corrosive due to the aforementioned cause.

Properties of Nitrating

The nitrating agent nitric acid is quite effective.

Nitro-methane is generated when HNO3 vapour is passed through methane (CH4) in the presence of Copper as a catalyst.

As a result, nitrate hydrocarbons are widely used in a variety of sectors for a variety of objectives.

Properties of Oxidation

Because nitric acid is a powerful oxidising agent, it can react strongly with metals, resulting in very explosive reactions.

At various concentrations, temperatures, and reducing agents, nitric acid can produce a variety of end products. With the exception of alloys, nitric acid may react with any metals.

It’s for this reason why it’s commonly employed in acid tests.

The degree of oxidation in nitric acid is determined by two factors: the acid’s concentration and the element’s nature.

The higher the oxidation, the lower the concentration level. To achieve increased oxidation, the element with which HNO3 will react must be extremely reactive.

Copper reacts with nitric acid to produce a variety of nitrogen-based chemicals. Cu, for instance, interacts with HNO3 to generate Nitrogen Dioxide (NO2) and nitrogen oxide (NO).

3Cu + 8HNO3 —-> 3Cu(NO3)2 + 2NO + 4H2O 3Cu(NO3)2 + 2NO + 4H2O

Cu [NO3]2 + 2NO2 + 2H2O —–> Cu [NO3]2 + 2NO2 + 2H2O

Nitrous oxide is formed when nitric acid is coupled with highly reactive magnesium, and ammonium nitrate is formed when nitric acid is combined with zinc.

—–> 4Mg [NO3]2 + N2O + 5H2O —–> 4Mg [NO3]2 + N2O + 5H2O

—–> 4Zn [NO3]2 + NH4NO3 + 3H2O = 4Zn [NO3]2 + NH4NO3 + 3H2O = 4Zn [NO3]2 + NH4NO3 + 3H2O = 4Zn [NO

Reactions with Non-Metallic Compounds

Except for nitrogen, oxygen, halogens, silicon, and noble gases, nitric acid interacts aggressively with all non-metals.

Non-metals are oxidised to the maximum oxidation state as acids by HNO3.

Nitric acid is a substance that can be used to treat a variety of ailments.

Nitric acid is a useful chemical with numerous industrial applications. It is, for example, a component of acid rain.

Nitric acid is also utilised in school laboratories to teach pupils about chemical characteristics. It is exclusively used in industry otherwise.

It is used to make ammonium nitrate, a common fertiliser.

It’s also utilised in the production of polymers and dyes.

Nitric acid is also used to make explosives such as nitroglycerin and TNT.

Nitric acid and hydrochloric acid are used to make aqua regia, a reagent used to dissolve gold and silver.

Nitric acid is also required for a colorimetric test to distinguish heroin from morphine.

Nitric acid also has a few medical applications.

Nitric acid is commonly used in woodworking to age trees like pine and maple artificially.

In the chemical industry, nitric acid is extensively utilised in the production of polymers such as polyamides and polyurethane.

Most importantly, nitric acid in various forms is utilised as an oxidizer in liquid-fueled rockets.


Nitric acid, often known as HNO3, is one of the most valuable compounds. However, due to its toxicity, it is usually not available in conventional stores.

Nonetheless, in the presence of your lab instructor, you can do tests in your school lab to determine the acidic nature of nitric acid. You may readily determine its acidic nature by checking its dissociation characteristic in water. You can learn a lot about nitric acid’s other properties using this method.

Read more: Molecular Geometry, Hybridization, and Polarity in HF Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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