Problem 133 - Chemistry Matter and Change

Question

Write the formula for the compounds made from each of the following pairs of ions. (Chapter 7\()\) $$\begin{array}{l}{\text { a. copper (I) and sulfite }} \\ {\text { b. } \operatorname{tin}(\mathrm{IV}) \text { and fluoride }} \\ {\text { c. gold(III) and cyanide }} \\ {\text { d. lead(II) and sulfide }}\end{array}$$

Step-by-Step Solution

Answer

The formulas are: a. \( \text{Cu}_2\text{SO}_3 \), b. \( \text{SnF}_4 \), c. \( \text{Au(CN)}_3 \), d. \( \text{PbS} \).

Step 1: Understanding the Ion Charges for Copper (I) and Sulfite

Copper (I) is represented as \( \text{Cu}^+ \), and sulfite is represented as \( \text{SO}_3^{2-} \). To create a neutral compound, the total positive and negative charges must balance. Therefore, two copper (I) ions are needed to balance one sulfite ion, resulting in the formula \( \text{Cu}_2\text{SO}_3 \).

Step 2: Determining the Compound Formula for Tin (IV) and Fluoride

Tin (IV) has a charge of \( \text{Sn}^{4+} \), while fluoride is \( \text{F}^- \). Four fluoride ions are required to balance the charge of one tin (IV) ion, leading to the compound \( \text{SnF}_4 \).

Step 3: Writing the Formula for Gold (III) and Cyanide

Gold (III) has a charge of \( \text{Au}^{3+} \), and the cyanide ion is represented as \( \text{CN}^- \). Three cyanide ions are needed to balance the charge of one gold (III) ion, resulting in the formula \( \text{Au(CN)}_3 \).

Step 4: Balancing Charges for Lead (II) and Sulfide

Lead (II) is \( \text{Pb}^{2+} \), while sulfide is \( \text{S}^{2-} \). Their charges balance in a one-to-one ratio, so the compound's formula is \( \text{PbS} \).

Key Concepts

Ion Charges

Understanding ion charges is essential when writing chemical formulas. Each ion carries a specific charge that results from an atom either losing or gaining electrons. The charge is depicted as a superscript number after the chemical symbol, either positive (+) or negative (-). For instance, a copper (I) ion, written as \( \text{Cu}^+ \), carries a positive charge of +1.

• Common cations include metal ions such as \( \text{Na}^+ \) or \( \text{Ca}^{2+} \).
• Anions, on the other hand, come from non-metals like \( \text{Cl}^- \) or oxyanions like \( \text{NO}_3^- \).

Knowing these charges helps us to determine how many ions of each type are needed to achieve a neutral compound. When writing chemical formulas, always ensure the total charge from the positive ions balances the total charge from the negative ions.

Compound Neutralization

Compound neutralization involves combining ions in such a way that the overall charge of the compound is zero. This means balancing the positive charges with the negative charges. The aim is to equalize the total amount of positive and negative charge.

• For example, in the compound \( \text{Cu}_2\text{SO}_3 \), two \( \text{Cu}^+ \) each with a +1 charge are needed to balance the single \( \text{SO}_3^{2-} \) which has a -2 charge.
• When the charges do not naturally balance, you adjust the number of ions needed from each element until neutralization occurs.

This method ensures that the resulting compound has no overall electrical charge, fulfilling the law of conservation of charge in chemical reactions.

Transition Metals

Transition metals are a group of elements located in the middle of the periodic table, known for their ability to form multiple ion charges. Unlike other elements, transition metals can possess several oxidation states, making them more versatile in forming compounds.

• For example, tin can be found as \( \text{Sn}^{2+} \) or \( \text{Sn}^{4+} \).
• This variability demands careful attention when writing chemical formulas, as the metal's charge must be considered precisely.

It is not uncommon for transition metals to require Roman numerals in their names to denote their specific charge, such as iron (II) for \( \text{Fe}^{2+} \) and iron (III) for \( \text{Fe}^{3+} \). Recognizing these charges is critical for correctly forming stable chemical compounds.

Polyatomic Ions

Polyatomic ions are ions that comprise more than one atom bonded together, carrying a net charge as a group. These ions are often nonmetals bonded with oxygen, like nitrate \( \text{NO}_3^- \) or sulfate \( \text{SO}_4^{2-} \). They are integral in constructing complex ionic compounds.

• Examples from the exercise include cyanide \( \text{CN}^- \) and sulfite \( \text{SO}_3^{2-} \).
• When writing chemical formulas involving polyatomic ions, use parentheses to indicate more than one of these ions is needed, for example, \( \text{Au(CN)}_3 \).

Recognizing polyatomic ions simplifies the process of writing chemical equations and helps in achieving accurate chemical compound formation. Mastery of polyatomic ions is critical for success in understanding compound structures in chemistry.