The molecular formula describes a chemical compound’s composition, identifying the types of elements present and the exact number of atoms that form a single molecule. The formula \(\text{HNO}_3\) represents a molecule of Nitric Acid.
Decoding the Formula: Counting Atoms in \(\text{HNO}_3\)
The molecular formula \(\text{HNO}_3\) is constructed using capital letters, where each letter signifies a distinct chemical element. The letter ‘H’ stands for Hydrogen, ‘N’ represents Nitrogen, and ‘O’ is the symbol for Oxygen. The formula thus immediately reveals that a molecule of Nitric Acid is built from three different elements.
The small numbers, known as subscripts, that follow an element’s symbol indicate the quantity of atoms of that element within the molecule. For the elements Hydrogen (H) and Nitrogen (N), there is no subscript written after their symbols. This absence of a subscript in chemical notation implies an understood value of ‘1,’ meaning there is one atom of Hydrogen and one atom of Nitrogen in the molecule.
In contrast, the symbol for Oxygen (O) is followed by the subscript ‘3.’ This states that each molecule of Nitric Acid contains three atoms of Oxygen. To find the total number of atoms in a single \(\text{HNO}_3\) molecule, one must simply sum the counts for each element. The calculation is 1 (Hydrogen) + 1 (Nitrogen) + 3 (Oxygen), which results in a total of five atoms per molecule.
Contextualizing \(\text{HNO}_3\): What is Nitric Acid?
Nitric acid, represented by the molecular formula \(\text{HNO}_3\), is classified as a strong mineral acid. In its pure state, it is a colorless liquid, although it often develops a yellowish-brown tint over time due to slight decomposition into nitrogen dioxide and water. It is volatile, corrosive, and acts as a powerful oxidizing agent.
This compound has a long history, sometimes referred to by the historical name “aqua fortis.” Today, it is a commodity chemical with extensive industrial applications, most of which leverage its strong acidity and oxidizing power. The single largest use of nitric acid is in the production of fertilizers, where it is neutralized with ammonia to create ammonium nitrate.
Fertilizer production accounts for the vast majority of the world’s industrially produced nitric acid. Beyond agriculture, it is a precursor for synthesizing many organic compounds, including various dyes and polymers such as nylon. Nitric acid is also a component in the manufacture of explosives like nitroglycerin and trinitrotoluene (TNT), and it is used in metallurgy for processes like metal cleaning, etching, and refining precious metals.