Problem 143 - Introductory Chemistry Atoms First

Question

What is the name of the polyatomic ion \(\mathrm{NO}_{3}^{-} ?\) What are the names of the acids \(\mathrm{HNO}_{3}\) and \(\mathrm{HNO}_{2} ?\)

Step-by-Step Solution

Answer

The polyatomic ion \(\mathrm{NO}_{3}^{-}\) is called nitrate. The corresponding acids are Nitric Acid (\(\mathrm{HNO}_{3}\)) and Nitrous Acid (\(\mathrm{HNO}_{2}\)).

Step 1: Identify the polyatomic ion

The polyatomic ion in question is \(\mathrm{NO}_{3}^{-}\).

Step 2: Name the polyatomic ion

The name of the polyatomic ion \(\mathrm{NO}_{3}^{-}\) is nitrate.

Step 3: Name the corresponding acids

The corresponding acids are \(\mathrm{HNO}_{3}\) and \(\mathrm{HNO}_{2}\). \(\mathrm{HNO}_{3}\) is the acid formed when nitrate (\(\mathrm{NO}_{3}^{-}\)) is combined with a hydrogen ion (\(\mathrm{H}^{+}\)). The name of this acid is Nitric Acid. \(\mathrm{HNO}_{2}\) is the acid formed from the nitrite ion (\(\mathrm{NO}_{2}^{-}\)), which has one less oxygen atom than the nitrate ion. The name of this acid is Nitrous Acid.

Key Concepts

Nitrate Ion

Understanding polyatomic ions can be challenging, but let's simplify it starting with the nitrate ion, which is denoted as \(\mathrm{NO}_{3}^{-}\). A nitrate is a polyatomic ion composed of one nitrogen atom (\(N\)) covalently bonded to three oxygen atoms (\(O\)). The entire molecule carries a negative charge, indicated by the superscript minus sign, which is balanced out when nitrate forms compounds with positive ions (cations).

Commonly found in fertilizers, the nitrate ion is essential for plant growth as it is a primary source of nitrogen, a crucial element for plants. However, high concentrations of nitrate in water supplies can be harmful to human health, leading to a condition known as methemoglobinemia or 'blue baby syndrome'. The presence of nitrate is also a significant indicator of water pollution, often stemming from agricultural runoff.

Nitric Acid

When a hydrogen ion (\(\mathrm{H}^{+}\)) bonds with a nitrate ion (\(\mathrm{NO}_{3}^{-}\)), we get nitric acid, which is chemically represented as \(\mathrm{HNO}_{3}\). This acid is highly reactive and corrosive, characterized by its sharp, pungent odor and its ability to react with metals, releasing hydrogen gas and forming metal nitrates.

It's vital to recognize that nitric acid plays a pivotal role in various industrial applications such as the production of fertilizers, explosives, and in the manufacturing of polyurethane foam. Furthermore, this powerful acid is used in a process called nitration, where it helps to introduce nitro groups into organic molecules, which is a key step in the synthesis of several pharmaceuticals and dyes.

Nitrous Acid

Stepping down from nitric acid is its close relative, nitrous acid, with the chemical formula \(\mathrm{HNO}_{2}\). This acid is less stable and weaker than nitric acid because it has one fewer oxygen atom attached to the nitrogen. You can generally find nitrous acid in solution or it is formed in situ; it's not commonly isolated in its pure form because it decomposes quickly.

Nitrous acid plays a significant role in atmospheric chemistry as well as in biochemistry. For instance, nitrous acid can act as an agent for nitrosation, a particular kind of chemical reaction that is essential for the synthesis of various organic compounds. It's important to observe lab safety protocols when dealing with nitrous acid due to its potential to form nitrosamines, which are known to be carcinogenic.