Problem 67 - Chemistry

Question

Name each of the following compounds: a. \(\mathrm{BaSO}_{3}\) c. \(\mathrm{KMnO}_{2}\) b. \(\mathrm{NaNO}_{2}\) d. \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\)

Step-by-Step Solution

Answer

a. Barium sulfite b. Sodium nitrite c. Potassium manganate(IV) d. Potassium dichromate

Step 1: a. Name \(\mathrm{BaSO}_{3}\)

This compound is composed of barium (\(\mathrm{Ba}\)) and the polyatomic ion sulfate (\(\mathrm{SO}_{3}\)). Barium has a +2 charge and sulfate has a -2 charge. So, the compound's name is Barium sulfite.

Step 2: b. Name \(\mathrm{NaNO}_{2}\)

This compound is composed of sodium (\(\mathrm{Na}\)) and the polyatomic ion nitrite (\(\mathrm{NO}_{2}\)). Sodium has a +1 charge and nitrite has a -1 charge. So, the compound's name is Sodium nitrite.

Step 3: c. Name \(\mathrm{KMnO}_{2}\)

This compound is composed of potassium (\(\mathrm{K}\)) and manganese(IV) oxide (\(\mathrm{MnO}_{2}\)). Potassium has a +1 charge and manganese(IV) oxide has a -1 charge. So, the compound's name is Potassium manganate(IV).

Step 4: d. Name \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\)

This compound is composed of potassium (\(\mathrm{K}\)) and the polyatomic ion dichromate (\(\mathrm{Cr}_{2} \mathrm{O}_{7}\)). Potassium has a +1 charge while dichromate has a -2 charge; hence, the compound has two potassium ions for each dichromate ion. The compound is named Potassium dichromate.

Key Concepts

Polyatomic Ions

Polyatomic ions are ions that consist of more than one atom. Unlike a single atom ion, these ions are bonded together and act as a single charged entity.
For example, in the compound \(\mathrm{BaSO}_{3}\), the group \(\mathrm{SO}_{3}\) represents the polyatomic ion sulfite. These ions are common in chemistry and have specific names that students should memorize.

Some examples of polyatomic ions include:

• Sulfate (\(\mathrm{SO}_{4}^{2-}\)) and sulfite (\(\mathrm{SO}_{3}^{2-}\))
• Nitrate (\(\mathrm{NO}_{3}^{-}\)) and nitrite (\(\mathrm{NO}_{2}^{-}\))
• Dichromate (\(\mathrm{Cr}_{2}\mathrm{O}_{7}^{2-}\))

Recognizing these polyatomic ions is crucial for correctly naming chemical compounds.

Charge of Ions

The charge of ions is a fundamental concept in chemical nomenclature. It is essential to know the charge of both single and polyatomic ions to name compounds accurately.
For instance, in \(\mathrm{KMnO}_{2}\), potassium \((\mathrm{K^{+}})\) and manganese(IV) oxide \((\mathrm{MnO}_{2}^{-})\) must balance each other for the compound to be stable.

Here's a quick guide to understanding charges:

• Cations: Positive ions, like \(\mathrm{K^{+}}\) and \(\mathrm{Na^{+}}\), often formed by metals losing electrons.
• Anions: Negative ions, like \(\mathrm{NO}_{2}^{-}\) and \(\mathrm{SO}_{3}^{2-}\), often formed by nonmetals gaining electrons.
• Polyatomic ions can have various charges based on their composition, such as \(\mathrm{Cr}_{2}\mathrm{O}_{7}^{2-}\).

Balancing these charges is key to forming neutral compounds and correctly naming them.

Compound Naming Conventions

Naming conventions are systematic ways to name chemical compounds. By following these conventions, you can derive the correct names from chemical formulas.
Let's look at the conventions using some examples:

• In \(\mathrm{BaSO}_{3}\), you name the metal cation first (Barium) followed by the polyatomic ion (Sulfite). Thus, it's called Barium sulfite.
• For \(\mathrm{NaNO}_{2}\), your metal is sodium and the ion is nitrite, resulting in Sodium nitrite.
• In compounds like \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\), write the metal (Potassium) first, then the polyatomic ion (Dichromate), making it Potassium dichromate.

Using these conventions ensures that chemical formulas are clearly and consistently communicated.