Problem 66 - Chemistry: The Central Science

Question

Name the following ionic compounds: (a) \(\mathrm{K}_{2} \mathrm{O}\), (b) \(\mathrm{NaClO}_{2}\), (c) \(\mathrm{Sr}(\mathrm{CN})_{2}\), (d) \(\mathrm{Co}(\mathrm{OH})_{2}\), (e) \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\) (f) \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3},(\mathrm{~g})\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{3}\), (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

(a) Potassium oxide, (b) Sodium chlorite, (c) Strontium cyanide, (d) Cobalt(II) hydroxide, (e) Iron(III) carbonate, (f) Chromium(III) nitrate, (g) Ammonium sulfite, (h) Sodium dihydrogen phosphate, (i) Potassium permanganate, (j) Silver(I) dichromate

Step 1: Identify cations and anions in the compounds

For each of the given compounds, let's identify the cation (positive ion) and the anion (negative ion) within the molecular formula. (a) \(\mathrm{K}_{2} \mathrm{O}\) : K (Cation), O (Anion) (b) \(\mathrm{NaClO}_{2}\) : Na (Cation), ClO\(_2\) (Anion) (c) \(\mathrm{Sr}(\mathrm{CN})_{2}\) : Sr (Cation), CN (Anion) (d) \(\mathrm{Co}(\mathrm{OH})_{2}\) : Co (Cation), OH (Anion) (e) \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\) : Fe (Cation), CO\(_3\) (Anion) (f) \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}\) : Cr (Cation), NO\(_3\) (Anion) (g) \(\left(\mathrm{NH}_{4}\right)_{2}\mathrm{SO}_{3}\) : NH\(_4\) (Cation), SO\(_3\) (Anion) (h) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\) : Na (Cation), H\(_2\)PO\(_4\) (Anion) (i) \(\mathrm{KMnO}_{4}\) : K (Cation), MnO\(_4\) (Anion) (j) \(\mathrm{Ag}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) : Ag (Cation), Cr\(_2\)O\(_7\) (Anion)

Step 2: Name the ionic compounds

Now, we will name each of the ionic compounds using the appropriate names for the cation and anion. (a) \(\mathrm{K}_{2} \mathrm{O}\): Potassium oxide (b) \(\mathrm{NaClO}_{2}\): Sodium chlorite (c) \(\mathrm{Sr}(\mathrm{CN})_{2}\): Strontium cyanide (d) \(\mathrm{Co}(\mathrm{OH})_{2}\): Cobalt(II) hydroxide (e) \(\mathrm{Fe}_{2}\left(\mathrm{CO}_{3}\right)_{3}\): Iron(III) carbonate (f) \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}\): Chromium(III) nitrate (g) \(\left(\mathrm{NH}_{4}\right)_{2}\mathrm{SO}_{3}\): Ammonium sulfite (h) \(\mathrm{NaH}_{2} \mathrm{PO}_{4}\): Sodium dihydrogen phosphate (i) \(\mathrm{KMnO}_{4}\): Potassium permanganate (j) \(\mathrm{Ag}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\): Silver(I) dichromate

Key Concepts

Cation and Anion Identification

Understanding how to identify cations and anions is essential for naming ionic compounds. Cations are ions with a positive charge, while anions have a negative charge. This results because atoms lose or gain electrons to become stable. In simple terms, cations are typically formed by metals, and anions are usually formed by non-metals or groups of atoms known as polyatomic ions.

• For example, in the compound \( \mathrm{K}_2 \mathrm{O} \), potassium (\( \mathrm{K} \)) is the cation as it has lost an electron, and oxygen (\( \mathrm{O} \)) is the anion as it has gained electrons.
• In \( \mathrm{NaClO}_2 \), sodium (\( \mathrm{Na} \)) is the cation, and the chlorite ion (\( \mathrm{ClO}_2^{-} \)) is the anion.
• Another example is \( \left( \mathrm{NH}_4 \right)_2 \mathrm{SO}_3 \), where the ammonium (\( \mathrm{NH}_4^+ \)) acts as the cation and sulfite (\( \mathrm{SO}_3^{2-} \)) acts as the anion.

Recognizing these components can help determine the formula and name the ionic compound accurately.

Chemical Nomenclature

Chemical nomenclature refers to the systematic naming of chemical substances. When it comes to ionic compounds, this often involves combining the names of the cation and the anion. The cation keeps its elemental name while the anion's name is modified, usually with a suffix.

• For binary compounds, the anion receives an '-ide' suffix. Hence, \( \mathrm{K}_2 \mathrm{O} \) is named potassium oxide.
• When working with polyatomic ions, use the ion's specific name. For example, \( \mathrm{NaClO}_2 \) is known as sodium chlorite; here, chlorite is the name of the polyatomic ion.
• Transition metals often require a Roman numeral indicating their charge. \( \mathrm{Fe}_2(\mathrm{CO}_3)_3 \) is called iron(III) carbonate because the iron cation here has a charge of +3.

Accurate chemical nomenclature is crucial in chemistry for clear communication of compound identities.

Ionic Compound Formulas

Constructing the correct formula for ionic compounds requires balancing the total positive and negative charges. This ensures the compound is electrically neutral.

• For instance, in \( \mathrm{Sr}(\mathrm{CN})_2 \), strontium has a charge of +2 and cyanide has a charge of -1. Two cyanide anions are needed to balance the charge of one strontium cation.
• Consider \( (\mathrm{NH}_4)_2 \mathrm{SO}_3 \): the ammonium ion carries a +1 charge and sulfite carries a -2 charge. Two ammonium ions balance the charge of one sulfite ion.
• In transition metal compounds, charge determination is key. \( \mathrm{Cr}(\mathrm{NO}_3)_3 \) shows chromium with a +3 charge balanced by three nitrate ions, each with a -1 charge.

By composing neutral formulas, we ensure correct representations of ionic structures and names.