Problem 71 - Chemistry The Central Science

Question

Name the following ionic compounds: (a) \(\mathrm{Li}_{2} \mathrm{O},(\mathbf{b})\) FeCl_ \((\mathbf{c}) \mathrm{NaClO},(\mathbf{d}) \quad \mathrm{CaSO}_{3}\)(e) \(\mathrm{Cu}(\mathrm{OH})_{2}, \quad(\mathbf{f}) \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}$$(\mathbf{g}) \mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2},(\mathbf{h}) \mathrm{Cr}_{2}\left(\mathrm{CO}_{3}\right)_{3}\)(i) \(\mathrm{K}_{2} \mathrm{CrO}_{4},(\mathbf{j})\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

(a) Lithium Oxide (b) Iron(I) Chloride (c) Sodium Hypochlorite (d) Calcium Sulfite (e) Copper(II) Hydroxide (f) Iron(II) Nitrate (g) Calcium Acetate (h) Chromium(III) Carbonate (i) Potassium Chromate (j) Ammonium Sulfate

Step 1: Identify cations and anions

For each ionic compound, identify the cation (positive ion) and anion (negative ion).

Step 2: Name cations and anions

Name the cations and anions found in the compounds, using the correct names for single ions or polyatomic ions.

Step 3: Combine cation and anion names

Combine the names of cations and anions to create the full name for each compound. If the compound contains a transition metal, specify its charge with Roman numerals. The names for the ionic compounds are: (a) Li₂O: \(Li^+\) is lithium and \(O^{2-}\) is oxide, so the name is Lithium Oxide. (b) FeCl: \(Fe\) is a transition metal so we must include its oxidation state with roman numerals. Since \(Cl^- \) is chloride and its charge is -1, thus the iron charge is +1, meaning the name is Iron(I) Chloride. (c) NaClO: \(Na^+\) is sodium and \(ClO^-\) is hypochlorite, so the name is Sodium Hypochlorite. (d) CaSO₃: \(Ca^{2+}\) is calcium and \(SO_3^{2-}\) is sulfite, so the name is Calcium Sulfite. (e) Cu(OH)₂: \(Cu\) is a transition metal, so we must include its oxidation state with roman numerals. Since each \(OH^-\) has a charge of -1 and there are two, the copper charge is +2, meaning the name is Copper(II) Hydroxide. (f) Fe(NO₃)₂: \(Fe\) is a transition metal, so we must include its oxidation state with roman numerals. Since each \(NO_3^-\) has a charge of -1 and there are two, the iron charge is +2, meaning the name is Iron(II) Nitrate. (g) Ca(CH₃COO)₂: \(Ca^{2+}\) is calcium and each \(CH_3COO^-\) is acetate, so the name is Calcium Acetate. (h) Cr₂(CO₃)₃: Cr is a transition metal, so we must include its oxidation state with roman numerals. Since each \(CO_3^{2-}\) has a charge of -2 and there are three, the total chromium charge is +6 (each Cr having a charge of +3), meaning the name is Chromium(III) Carbonate. (i) K₂CrO₄: \(K^+ \) is potassium and \(CrO_4^{2-}\) is chromate, so the name is Potassium Chromate. (j) (NH₄)₂SO₄: \((NH_4^+)\) is ammonium and \(SO_4^{2-}\) is sulfate, so the name is Ammonium Sulfate.

Key Concepts

Cation and Anion Identification

Understanding the basic components of ionic compounds is key to naming them. An ionic compound consists of positively charged cations and negatively charged anions.

Take, for instance, the compound \( \mathrm{NaCl} \). Here, \( \mathrm{Na}^+ \) is the cation, which is a sodium ion, and \( \mathrm{Cl}^- \) is the anion, a chloride ion. In identifying cations and anions, always remember that cations carry a positive charge and are usually metals or polyatomic ions like ammonium, while anions carry a negative charge and can either be non-metals or polyatomic ions such as sulfate or nitrate.

To correctly name the compound, you must accurately identify these charged species, which then dictate the nomenclature used.

Polyatomic Ions

Polyatomic ions are ions that consist of more than one atom, and they can be either cations or anions. Unlike monatomic ions, which are composed of single atoms, polyatomic ions have molecules that carry a charge.

For example, the sulfate ion \( \mathrm{SO}_4^{2-} \) is made up of one sulfur atom and four oxygen atoms, and carries a net charge of -2. Recognizing common polyatomic ions like sulfate, nitrate \( \mathrm{NO}_3^- \) and hydroxide \( \mathrm{OH}^- \) is essential. When a compound contains polyatomic ions, you name it by stating the cation followed by the name of the polyatomic anion, such as in Ammonium Sulfate \( \left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4 \), where \( \left(\mathrm{NH}_4\right)^+ \) is the polyatomic cation and \( \mathrm{SO}_4^{2-} \) is the polyatomic anion.

Transition Metal Oxidation States

Transition metals often have multiple possible oxidation states, which makes naming their compounds a bit more challenging. The oxidation state of a transition metal in a compound is indicated using Roman numerals in parentheses right after the metal's name.

For instance, iron can have an oxidation state of +2 or +3. When iron pairs with the chloride ion \( \mathrm{Cl}^- \) to form \( \mathrm{FeCl}_2 \), it is in the +2 oxidation state and thus named Iron(II) Chloride. It is crucial to examine the anions in the compound to determine the oxidation state of the metal, ensuring that the overall charge of the ionic compound is neutral.

Chemical Nomenclature

Chemical nomenclature is the standardized process for naming chemical compounds. To name an ionic compound, start with the name of the cation followed by the anion. If the cation is a metal with a fixed charge, like sodium or magnesium, just state its name. If it is a transition metal with variable charges, like iron or copper, then determine the oxidation state and use Roman numerals.

For the anion, if it is a single element, change its ending to '-ide,' like oxide or chloride. For polyatomic anions, use the established names like sulfate or nitrate.

Combining Names

Take the example of \( \mathrm{Cu}\left(\mathrm{OH}\right)_2 \), where copper has a +2 oxidation state and the hydroxide is a polyatomic anion. The correct name would be Copper(II) Hydroxide, combining the cation's name and its oxidation state with the polyatomic anion's name.