Problem 105 - Chemistry The Molecular Nature of Matter

Question

Name the following. If necessary, refer to Table 2.4 in Section 2.5. (a) \(\mathrm{NaNO}_{2},\) (b) \(\mathrm{KMnO}_{4},\) (c) \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O},\) (d) KSCN

Step-by-Step Solution

Answer

(a) Sodium Nitrite, (b) Potassium Permanganate, (c) Magnesium Sulfate Heptahydrate, (d) Potassium Thiocyanate.

Step 1 - Understanding the Compounds

First, identify the elements and any polyatomic ions in the compounds. Use Table 2.4 to find the names of polyatomic ions if they are present.

Step 2 - Naming Ionic Compounds

To name ionic compounds, name the metal (cation) first, then the non-metal (anion), changing the end of the non-metal to '-ide' if it's a single element or using the polyatomic ion's name if one is present.

Step 3 - Naming Hydrates

When a compound has water molecules attached (a hydrate), after naming the compound, follow with the appropriate prefix for the number of water molecules and the word 'hydrate'.

Step 4 - Name Each Compound

For each compound:(a) \(\mathrm{NaNO}_{2}\) is named Sodium Nitrite.(b) \(\mathrm{KMnO}_{4}\) is named Potassium Permanganate.(c) \(\mathrm{MgSO}_{4} \cdot 7\mathrm{H}_{2} \mathrm{O}\) is named Magnesium Sulfate Heptahydrate.(d) KSCN is named Potassium Thiocyanate.

Key Concepts

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms that are covalently bonded, or metal complexes that can be considered to be acting as a single unit in the context of acid and base chemistry or in the formation of salts. An essential aspect of understanding ionic compounds is recognizing that many of the compounds contain polyatomic ions.

For instance, in the compound \( \mathrm{NaNO}_{2} \), the ion \( \mathrm{NO}_{2}^{-} \) is known as nitrite, which is a polyatomic ion. Similarly, in \( \mathrm{KMnO}_{4} \) the ion \( \mathrm{MnO}_{4}^{-} \) is the polyatomic ion called permanganate. Students need to be familiar with common polyatomic ions to name such ionic compounds correctly. As seen in the steps from the textbook solution, consulting a reference table like Table 2.4 is often necessary to identify these ions correctly.

Hydrates Chemistry

In chemistry, hydrates are compounds that include water molecules tightly bound to the crystal structure of the salt. These water molecules can be a key part of the compound's identity and properties. The naming of hydrates follows a specific convention where the number of water molecules is indicated by a prefix, and the word 'hydrate' is added at the end of the compound's name.

The prefixes are derived from Greek numerals; for instance, 'hepta-' refers to seven so a compound with seven water molecules, like \( \mathrm{MgSO}_{4} \cdot 7\mathrm{H}_{2} \mathrm{O} \) in the given exercise, is called Magnesium Sulfate Heptahydrate. The water of hydration is essential to the formation of some specific crystal structures and can often be removed by heating, a process known as dehydration.

Compound Nomenclature

Compound nomenclature is the systematic naming of chemical compounds that follow specific rules. For ionic compounds, the name typically begins with the cation (usually a metal), followed by the anion (a non-metal or a polyatomic ion). If the anion is a single element, its name is altered to end with '-ide', such as in potassium chloride \( \mathrm{KCl} \), where chlorine becomes chloride.

When dealing with compound names, specificity is essential in conveying the exact chemical composition. The exercise demonstrates this, as seen in how \( \mathrm{NaNO}_{2} \) and \( \mathrm{KMnO}_{4} \) are named Sodium Nitrite and Potassium Permanganate, respectively, while KSCN is called Potassium Thiocyanate indicating that SCN is the thiocyanate ion. Understanding the nomenclature rules is crucial for students to communicate accurately in chemistry.