Problem 80 - Chemistry and Chemical Reactivity

Question

Name two anions that combine with \(\mathrm{Al}^{3+}\) ion to produce water- soluble compounds.

Step-by-Step Solution

Answer

Common anions like nitrate (\(\mathrm{NO}_3^-\)) and perchlorate (\(\mathrm{ClO}_4^-\)) form water-soluble compounds with \(\mathrm{Al}^{3+}\).

Step 1: Understand Aluminum Ion

The given ion is the aluminum ion, denoted as \( \mathrm{Al}^{3+} \). This is a cation with a 3+ charge, indicating it can combine with anions to form compounds.

Step 2: Identify Soluble Compounds

To find anions that form water-soluble compounds with \( \mathrm{Al}^{3+} \), recall common solubility rules. Anions that often form soluble compounds include perchlorate (\( \mathrm{ClO}_4^- \)) and nitrate (\( \mathrm{NO}_3^- \)). Both tend to form water-soluble compounds regardless of the accompanying cation.

Step 3: Combine Anions with Aluminum Ion

Combine each identified anion with the \( \mathrm{Al}^{3+} \) ion. With perchlorate, the compound formed is \( \mathrm{Al(ClO}_4)_3 \). With nitrate, the compound formed is \( \mathrm{Al(NO}_3)_3 \). Both are known to be highly soluble in water.

Key Concepts

Aluminum Ion

The aluminum ion, represented as \( \mathrm{Al}^{3+} \), is a very common cation in chemistry. Cations are positively charged ions, and the number \( 3+ \) indicates that the aluminum ion has lost three electrons. This gives it a positive charge of three. Because it is a cation, aluminum is eager to interact with anions, which are negatively charged ions. This interaction helps to stabilize the compound created.

• The charge of \( \mathrm{Al}^{3+} \) plays a critical role in how it bonds with other ions.
• Being a metal, aluminum usually donates electrons, making it a stable ion.
• Its positive charge means it can form bonds with anions which have a total charge of \(-3\). This creates neutral compounds where the charges balance out.

Understanding aluminum ions is crucial when studying the formation of ionic compounds and predicting their properties, such as solubility.

Anions

Anions are ions that carry a negative charge. This charge results from an atom gaining extra electrons. In the context of combining with aluminum ions, anions play a key role in forming ionic compounds. Two anions that are often examined in relation to solubility with aluminum ions are perchlorate (\( \mathrm{ClO}_4^- \)) and nitrate (\( \mathrm{NO}_3^- \)).

• Perchlorate, \( \mathrm{ClO}_4^- \), is a type of oxyanion. It's known for forming stable, soluble ionic compounds with many cations including \( \mathrm{Al}^{3+} \).
• Nitrate, \( \mathrm{NO}_3^- \), is another common anion that combines well with a variety of cations and is almost always soluble in water.

In chemical reactions, the role of anions is to balance the positive charge from cations like aluminum, forming stable and often water-soluble compounds.

Solubility Rules

Solubility rules are guidelines that indicate whether a compound will dissolve in water, creating a solution. These rules are essential for predicting the behavior of ionic compounds in aquatic environments. The solubility of a compound depends on the combination of ions it contains, particularly on the specific anions in question.

• Compounds containing nitrate (\( \mathrm{NO}_3^- \)) and perchlorate (\( \mathrm{ClO}_4^- \)) anions are generally soluble in water. This makes them reliable choices for forming soluble compounds with various cations, such as \( \mathrm{Al}^{3+} \).
• The rule of thumb is that if a compound contains an alkali metal cation or ammonium, it typically dissolves in water. However, certain anions like nitrate and perchlorate ensure solubility irrespective of the cation.

Knowing these solubility rules allows chemists to predict which ionic compounds will dissolve in water, thus understanding their potential applications in various chemical reactions and real-world applications.