Problem 13 - Chemistry and Chemical Reactivity

Question

For each of the following compounds, give the formula, charge, and the number of each ion that makes up the compound: (a) \(\mathrm{K}_{2} \mathrm{S}\) (b) \(\cos \mathrm{O}_{4}\) (c) \(\mathrm{KMnO}_{4}\) (d) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\) (e) \(\mathrm{Ca}(\mathrm{ClO})_{2}\)

Step-by-Step Solution

Answer

(a) 2 K\(^+\), 1 S\(^{2-}\); (b) 1 Co\(^{2+}\), 1 SO\(_4^{2-}\); (c) 1 K\(^+\), 1 MnO\(_4^{-}\); (d) 3 NH\(_4^+\), 1 PO\(_4^{3-}\); (e) 1 Ca\(^{2+}\), 2 ClO\(^-\).

Step 1: Identify Ions in Compound (a)

For compound \( \mathrm{K}_2\mathrm{S} \):- Potassium (K) is a Group 1 element, which typically forms a +1 charge ion.- Sulfide (S) is the anion from sulfur, which typically forms a -2 charge ion.The number of ions in this compound are 2 K\(^+\) ions and 1 S\(^{2-}\) ion.

Step 2: Identify Ions in Compound (b)

For compound, \( \text{CoSO}_4 \):- Cobalt (Co) typically exists in +2 oxidation state to balance out the sulfate.- Sulfate (SO\(_4\)) is a polyatomic ion with a -2 charge.The number of ions in this compound are 1 Co\(^{2+}\) ion and 1 \( \text{SO}_4^{2-} \) ion.

Step 3: Identify Ions in Compound (c)

For compound \( \text{KMnO}_4 \):- Potassium (K) typically forms a +1 charge ion.- Permanganate \((\text{MnO}_4)\) is a polyatomic ion with a -1 charge.The number of ions in this compound are 1 K\(^+\) ion and 1 \( \text{MnO}_4^{-} \) ion.

Step 4: Identify Ions in Compound (d)

For compound \( (\text{NH}_4)_3\text{PO}_4 \):- Ammonium \((\text{NH}_4)\) is a polyatomic ion with a +1 charge.- Phosphate \((\text{PO}_4)\) is a polyatomic ion with a -3 charge.The number of ions in this compound are 3 \( \text{NH}_4^+ \) ions and 1 \( \text{PO}_4^{3-} \) ion.

Step 5: Identify Ions in Compound (e)

For compound \( \text{Ca(ClO)}_2 \):- Calcium (Ca) is a Group 2 element, which typically forms a +2 charge ion.- Hypochlorite \((\text{ClO})\) is a polyatomic ion with a -1 charge.The number of ions in this compound are 1 Ca\(^{2+}\) ion and 2 \( \text{ClO}^{-} \) ions.

Key Concepts

Ion Charges

Understanding ion charges is essential for predicting how different ions in a chemical formula interact with each other. Ions are atoms or molecules that carry a charge, resulting from the loss or gain of electrons. The charge is denoted by a superscript next to the chemical symbol. For instance, a +1 charge is written as K\(^+\), while a -2 charge is written as S\(^{2-}\). Many elements have typical charges based on their position in the periodic table:

• Group 1 elements (like Potassium) usually form +1 ions.
• Group 2 elements (like Calcium) typically carry a +2 charge.
• Nonmetals, such as Sulfur, often form negative ions like S\(^{2-}\).

Recognizing these charges helps to deduce the neutral composition of compounds. When forming compounds, these charges must balance to result in a neutral overall charge. By noting the charge of each ion, students can better understand the structure of the compounds they are studying.

Polyatomic Ions

Polyatomic ions are charged entities composed of several atoms bonded together that act as a single unit. These ions are important in chemistry because they appear frequently and have specific charges that need to be memorized. For example, commonly encountered polyatomic ions include:

• Sulfate (SO\(_4\)) with a charge of -2.
• Permanganate (MnO\(_4\)) with a charge of -1.
• Ammonium (NH\(_4\)) with a charge of +1.
• Phosphate (PO\(_4\)) with a charge of -3.
• Hypochlorite (ClO) with a charge of -1.

The charges on these polyatomic ions add complexity to the compound's formula, as they must also balance with the charges of other ions present to maintain electrical neutrality. Memorizing these common polyatomic ions and understanding their charge relationships can significantly simplify the process of writing and interpreting chemical formulas.

Compound Composition

The composition of a compound is determined by the arrangement and number of ions in its formula. Each compound is neutral overall, meaning the total positive charge must equal the total negative charge. By analyzing the composition, students can determine how many of each ion type are present in a compound. Let's look at some examples:

• In K\(_2\)S, the compound contains two Potassium ions (K\(^+\)) and one Sulfide ion (S\(^{2-}\)). The charges add up to zero, achieving electrical neutrality.
• CoSO\(_4\) requires one Cobalt ion (Co\(^{2+}\)) to balance the -2 charge of the Sulfate ion (SO\(_4\)).
• In (NH\(_4\))\(_3\)PO\(_4\), three Ammonium ions (NH\(_4^+\)) balance out the charge of one Phosphate ion (PO\(_4^{3-}\)).

Understanding compound composition involves knowing both the individual ion charges and how they combine to form a neutral compound. This knowledge is fundamental for comprehending the formation and properties of various substances in chemistry.