Question

Correctly name each of these ionic compounds. (a) \(\mathrm{K}_{2} \mathrm{~S}\) (b) \(\mathrm{NiSO}_{4}\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\) (d) \(\mathrm{Al}(\mathrm{OH})_{3}\) (e) \(\mathrm{Co}_{2}\left(\mathrm{SO}_{4}\right)_{3}\)

Short answer

(a) Potassium sulfide, (b) Nickel(II) sulfate, (c) Ammonium phosphate, (d) Aluminum hydroxide, (e) Cobalt(III) sulfate.

Step-by-step solution

Naming the Compound with Potassium and Sulfur

The formula \( \mathrm{K}_2 \mathrm{S} \) consists of potassium ions \( \mathrm{K}^+ \) and sulfide ions \( \mathrm{S}^{2-} \). Since potassium forms a single type of ion, we name it simply as potassium sulfide.

Naming the Compound with Nickel and Sulfate

The formula \( \mathrm{NiSO}_4 \) contains \( \mathrm{Ni}^{2+} \) ions and sulfate ions \( \mathrm{SO}_4^{2-} \). Nickel commonly forms \( \mathrm{Ni}^{2+} \), so this compound is named nickel(II) sulfate.

Naming the Compound with Ammonium and Phosphate

The formula \( (\mathrm{NH}_4)_3 \mathrm{PO}_4 \) has ammonium ions \( \mathrm{NH}_4^+ \) and phosphate ions \( \mathrm{PO}_4^{3-} \). As \( \mathrm{NH}_4^+ \) is a common polyatomic ion and \( \mathrm{PO}_4^{3-} \) is a common polyatomic ion, it is named ammonium phosphate.

Naming the Compound with Aluminum and Hydroxide

The compound \( \mathrm{Al(OH)}_3 \) comprises \( \mathrm{Al}^{3+} \) ions and hydroxide ions \( \mathrm{OH}^- \). Thus, the compound is named aluminum hydroxide.

Naming the Compound with Cobalt and Sulfate

The formula \( \mathrm{Co}_2(\mathrm{SO}_4)_3 \) involves \( \mathrm{Co}^{3+} \) ions and \( \mathrm{SO}_4^{2-} \) ions. The oxidation state of cobalt in this compound is +3, so it is named cobalt(III) sulfate.

Key concepts

Potassium Sulfide

Potassium sulfide is an ionic compound composed of potassium ions and sulfide ions. To delve deeper, let's break down the formula: - **Potassium ions**: Potassium, an alkali metal, carries a single positive charge, depicted as \( \mathrm{K}^+ \).- **Sulfide ions**: Sulfur forms ions with a 2- charge, represented as \( \mathrm{S}^{2-} \).When these ions form a compound, two potassium ions are needed to balance one sulfide ion, resulting in the formula \( \mathrm{K}_2 \mathrm{S} \). Thus, putting them together, the name of the compound is potassium sulfide. The naming is straightforward as potassium forms only one type of cation. This simplicity makes it easier to identify and name compounds with such ions.

Nickel(II) Sulfate

Nickel(II) sulfate includes nickel divalent ions and sulfate ions. Let's examine its components: - **Nickel ions**: Nickel can have multiple oxidation states. In this case, the nickel ion is \( \mathrm{Ni}^{2+} \).- **Sulfate ions**: This is a common polyatomic ion with a formula of \( \mathrm{SO}_4^{2-} \).The compound's formula is \( \mathrm{NiSO}_4 \), signifying that one nickel ion is paired with a sulfate ion. The "(II)" in nickel(II) sulfate is crucial. It specifies the nickel ion's +2 oxidation state, which is essential for correctly naming compounds with elements that have multiple oxidation states. Understanding this helps in appropriately naming similar compounds.

Ammonium Phosphate

Ammonium phosphate brings together ammonium and phosphate ions to form a stable compound. Here's a closer look: - **Ammonium ions**: These are polyatomic ions represented as \( \mathrm{NH}_4^+ \).- **Phosphate ions**: These carry a 3- charge and are expressed as \( \mathrm{PO}_4^{3-} \).The formula \( (\mathrm{NH}_4)_3 \mathrm{PO}_4 \) tells us that three ammonium ions are required to balance one phosphate ion. This compound is named ammonium phosphate, indicating the ions present and reflecting their ratios. Such naming is helpful for remembering how different polyatomic ions combine and the resulting formulas they produce.

Aluminum Hydroxide

Aluminum hydroxide is made up of aluminum ions and hydroxide ions. Here's the breakdown: - **Aluminum ions**: Represented as \( \mathrm{Al}^{3+} \), these have a 3+ charge.- **Hydroxide ions**: Denoted by \( \mathrm{OH}^- \), these have a 1- charge.The formula \( \mathrm{Al(OH)}_3 \) means each aluminum ion combines with three hydroxide ions to balance the charges. Aluminum hydroxide's name is clear and direct, indicating exactly what ions are present. This clarity is particularly useful for students learning to name compounds correctly while understanding the charge balance needed in ionic compounds.