Question

Pair each cation on the left with an anion on the right that will form an insoluble compound with it and write a formula for the insoluble compound. Use each anion only once. $$ \begin{array}{ll} \mathrm{Ag}^{+} & \mathrm{SO}_{4}{ }^{2-} \\ \mathrm{Ba}^{2+} & \mathrm{Cl}^{-} \\ \mathrm{Cu}^{2+} & \mathrm{CO}_{3}{ }^{2-} \\ \mathrm{Fe}^{3+} & \mathrm{S}^{2-} \end{array} $$

Short answer

The insoluble compounds formed are AgCl, BaSO4, CuCO3, and Fe2S3.

Step-by-step solution

Review Solubility Rules

Familiarize yourself with common solubility rules. These will help determine which combinations of cations and anions result in insoluble compounds. Generally, compounds containing SO4(2-) are soluble, except those with Ba2+, Pb2+, Hg2+, and Sr2+. Ag+ typically forms insoluble compounds with Cl-. Cu2+ forms insoluble compounds with CO3(2-) and Fe3+ forms insolubile compounds with S2-.

Match Cations to Anions

According to the solubility rules: 1. Ag+ will form an insoluble compound with Cl-, which is AgCl. 2. Ba2+ forms an insoluble compound with SO4(2-), which is BaSO4. 3. Cu2+ forms an insoluble compound with CO3(2-), which is CuCO3. 4. Fe3+ will form an insoluble compound with S2-, which is Fe2S3.

Write Formulas for the Insoluble Compounds

Write down the chemical formulas of the corresponding insoluble compounds. Make sure the formulas are balanced in terms of charge: 1. Silver chloride - AgCl 2. Barium sulfate - BaSO4 3. Copper(II) carbonate - CuCO3 4. Iron(III) sulfide - Fe2S3

Key concepts

Solubility Rules

Understanding solubility rules is the first step in predicting when a chemical reaction will result in the formation of an insoluble compound. These rules are a set of guidelines that chemists use to determine the solubility of different ionic compounds in water. For instance, most sodium (Na+) compounds are soluble, while compounds with silver (Ag+) are often insoluble exceptions, especially with chloride (Cl−).

In the context of our exercise, knowing that compounds with sulfate (SO4 2−) are usually soluble with exceptions such as barium (Ba2+), and that silver forms an insoluble compound with chloride, leads us to conclude that barium sulfate (BaSO4) and silver chloride (AgCl) will precipitate. These insights are critical for students to be able to predict the outcomes of ionic reactions in aqueous solutions.

Precipitate Formation

Precipitate formation occurs when two aqueous solutions containing dissolved ions are mixed and an insoluble ionic compound is formed. This compound, the precipitate, settles out of the solution or can be seen as a cloudiness. For example, mixing a solution with silver ions (Ag+) and another with chloride ions (Cl−) results in the formation of silver chloride (AgCl), a white solid that falls out of the solution.

In our textbook problem, we identify pairs of ions that will form a precipitate when combined. It's useful for students to visualize this process by imagining two clear solutions becoming turbid as insoluble particles appear and settle, such as the case when copper(II) carbonate (CuCO3) or iron(III) sulfide (Fe2S3) are formed.

Ionic Compound Formulas

Ionic compound formulas represent the proportion of cations to anions that balance the total charge in the compound. Writing the correct formula involves ensuring that the positive and negative charges equal zero when summed. For instance, in the compound copper(II) carbonate (CuCO3), the copper ion has a charge of 2+ while the carbonate ion has a charge of 2−. One of each ion balances the charges, resulting in a neutral compound.

For students, understanding how to balance ionic charges is essential. Here, being able to identify that iron(III) sulfide (Fe2S3) requires two iron(III) ions (each with a 3+ charge) to balance three sulfide ions (each with a 2− charge) is a key skill in correctly formulating the compound.

Cation-Anion Pairing

Cation-anion pairing is a fundamental concept in ionic chemistry, involving the combination of positively charged ions (cations) with negatively charged ions (anions) to form ionic compounds. The pairs are formed based on the principle of charge neutrality, where the total positive charge must balance the total negative charge.

It's crucial for students to practice pairing the correct cation with its counter anion. In the exercise, we see specific pairs that follow this rule to form insoluble compounds. For instance, Ag+ (a cation) pairs with Cl− (an anion) to form AgCl, which precipitates out of solution. Mastering this pairing helps students predict and write chemical formulas for reactions and understand the nature of chemical bonds in ionic compounds.