Problem 72 - Chemistry: The Central Science

Question

Name the following ionic compounds: (a) \(\mathrm{KCN}\), (b) \(\mathrm{NaBrO}_{2}\), (c) \(\mathrm{Sr}(\mathrm{OH})_{2}\), (d) \(\mathrm{CoTe}\), (e) \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\), (f) \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}\), (g) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{3}\), (h) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\), (i) \(\mathrm{KMnO}_{4}\), (j) \(\mathrm{Ag}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\).

Step-by-Step Solution

Answer

The names of the ionic compounds are: (a) potassium cyanide, (b) sodium bromite, (c) strontium hydroxide, (d) cobalt(II) telluride or cobalt(III) telluride, (e) iron(III) carbonate, (f) chromium(III) nitrate, (g) ammonium sulfite, (h) sodium dihydrogen phosphate, (i) potassium permanganate, (j) silver(I) dichromate.

Step 1: a) Naming \(\mathrm{KCN}\)

In this compound, we have a potassium ion (K+) and a cyanide ion (CN-). The chemical name for this compound is "potassium cyanide."

Step 2: b) Naming \(\mathrm{NaBrO}_{2}\)

In this compound, we have a sodium ion (Na+) and a bromite ion (BrO2-). The chemical name for this compound is "sodium bromite."

Step 3: c) Naming \(\mathrm{Sr}(\mathrm{OH})_{2}\)

In this compound, we have a strontium ion (Sr2+) and a hydroxide ion (OH-). The chemical name for this compound is "strontium hydroxide."

Step 4: d) Naming \(\mathrm{CoTe}\)

In this compound, we have a cobalt ion (Co2+ or Co3+) and a telluride ion (Te2-). We do not know the oxidation state of the cobalt ion, so we use roman numbers to express it: the chemical name for this compound is "cobalt(II) telluride" or "cobalt(III) telluride."

Step 5: e) Naming \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\)

In this compound, we have an iron ion (Fe3+) and carbonate ion (CO3 2-). The chemical name for this compound is "iron(III) carbonate."

Step 6: f) Naming \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}\)

In this compound, we have a chromium ion (Cr3+) and nitrate ion (NO3-). The chemical name for this compound is "chromium(III) nitrate."

Step 7: g) Naming \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{3}\)

In this compound, we have an ammonium ion (NH4+) and a sulfite ion (SO3 2-). The chemical name for this compound is "ammonium sulfite."

Step 8: h) Naming \(\mathrm{NaH}_{2}\mathrm{PO}_{4}\)

In this compound, we have a sodium ion (Na+) and a dihydrogen phosphate ion (H2PO4-). The chemical name for this compound is "sodium dihydrogen phosphate."

Step 9: i) Naming \(\mathrm{KMnO}_{4}\)

In this compound, we have a potassium ion (K+) and a permanganate ion (MnO4-). The chemical name for this compound is "potassium permanganate."

Step 10: j) Naming \(\mathrm{Ag}_{2}\mathrm{Cr}_{2} \mathrm{O}_{7}\)

In this compound, we have a silver ion (Ag+) and a dichromate ion (Cr2O7 2-). The chemical name for this compound is "silver(I) dichromate."

Key Concepts

Chemical Nomenclature

Understanding chemical nomenclature is essential for studying chemistry, as it is the system used to name chemical compounds. The naming of ionic compounds, which consist of positively charged cations and negatively charged anions, follows specific rules. First, the cation (usually a metal or a positively charged polyatomic ion) is named, followed by the anion (a nonmetal or a negatively charged polyatomic ion).

For monatomic cations, the element name is used, such as sodium or potassium. For monatomic anions, the element name ends in '-ide,' such as chloride for Cl- or oxide for O2-. When dealing with transition metals that can have multiple oxidation states, Roman numerals indicate the positive charge of the cation, for example, iron(III) for Fe3+.

In naming polyatomic ions, you would use their specific names, like nitrate for NO3- or sulfate for SO42-. Overall, the key to mastering chemical nomenclature is to learn the names and charges of the common ions and apply systematic rules when naming different types of compounds.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded or of a metal complex that act as a single unit with a net charge. Knowing the names and formulas of common polyatomic ions is crucial because they often appear in various ionic compounds.

Examples include the hydroxide ion (OH-), the sulfate ion (SO42-), and the ammonium ion (NH4+). Compounds such as potassium permanganate (KMnO4) and sodium bromite (NaBrO2) also contain polyatomic ions. Understanding the composition and charge of these ions helps in predicting the formulae of the compounds they form. When these ions combine with other cations or anions, they do not change their names. Therefore, a solid grasp of polyatomic ions is vital for constructing and understanding the names of ionic compounds.

Oxidation States

Oxidation states, also known as oxidation numbers, provide insight into the electron distribution within compounds and help with understanding the nomenclature of chemical compounds, especially those containing transition metals with multiple possible charges.

The oxidation state is a number assigned to an element in a chemical combination which represents the number of electrons lost or gained by an atom of that element in the compound. For example, in iron(III) carbonate (Fe2(CO3)3), the numeral III indicates iron has an oxidation state of +3.

In compounds like cobalt telluride (CoTe), where cobalt can exhibit more than one possible oxidation state, the actual oxidation state must be specified as cobalt(II) or cobalt(III). Simple ions have oxidation states equal to their charge, while neutral compounds always have a net oxidation state of zero. A clear grasp of oxidation states is crucial to both naming compounds correctly and understanding their chemical behavior.