Problem 37 - Chemistry The Molecular Science

Question

Aluminum is obtained from bauxite, which is not a specific mineral but a name applied to a mixture of minerals. One of those minerals, which can dissolve in acids, is gibbsite, \(\mathrm{Al}(\mathrm{OH})_{3} .\) Write balanced overall and net ionic equations for the reaction of gibbsite with sulfuric acid.

Step-by-Step Solution

Answer

Overall: \( 2 \mathrm{Al}(\mathrm{OH})_3 + 3 \mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{Al}_2(\mathrm{SO}_4)_3 + 6 \mathrm{H}_2\mathrm{O} \); Net ionic: \( 2 \mathrm{Al}(\mathrm{OH})_3 + 6 \mathrm{H}^+ \rightarrow 2 \mathrm{Al}^{3+} + 6 \mathrm{H}_2\mathrm{O} \).

Step 1: Identify the Chemical Reaction

Gibbsite, \(\mathrm{Al}(\mathrm{OH})_3\), reacts with sulfuric acid, \(\mathrm{H}_2\mathrm{SO}_4\). Sulfuric acid is a strong acid that can provide \(2\ \mathrm{H}^+\) ions in solution. The reaction involves \(\mathrm{Al}(\mathrm{OH})_3\) acting as a base and reacting with the acid H\(\mathrm{H}_2\mathrm{SO}_4\) to form aluminum sulfate and water.

Step 2: Write the Overall Balanced Equation

The overall chemical reaction between gibbsite and sulfuric acid can be written as:\[ 2 \mathrm{Al}(\mathrm{OH})_3 (s) + 3 \mathrm{H}_2\mathrm{SO}_4 (aq) \rightarrow \mathrm{Al}_2(\mathrm{SO}_4)_3 (aq) + 6 \mathrm{H}_2\mathrm{O} (l) \]We have two \(\mathrm{Al}(\mathrm{OH})_3\) reacting with three \(\mathrm{H}_2\mathrm{SO}_4\) to form one molecule of \(\mathrm{Al}_2(\mathrm{SO}_4)_3\) and six molecules of water.

Step 3: Identify Dissociated Ions in Aqueous Solution

In aqueous solutions, sulfuric acid \( \mathrm{H}_2\mathrm{SO}_4\) dissociates into \(2\ \mathrm{H}^+\) ions and \( \mathrm{SO}_4^{2-} \) ions. Aluminum sulfate \( \mathrm{Al}_2(\mathrm{SO}_4)_3\) dissociates into \(2 \mathrm{Al}^{3+}\) ions and \(3 \mathrm{SO}_4^{2-} \) ions.

Step 4: Write the Net Ionic Equation

The net ionic equation focuses on the species that undergo change in the reaction.\[ 2 \mathrm{Al}(\mathrm{OH})_3(s) + 6 \mathrm{H}^+(aq) \rightarrow 2 \mathrm{Al}^{3+}(aq) + 6 \mathrm{H}_2\mathrm{O}(l) \]The \(\mathrm{SO}_4^{2-}\) ions are spectator ions and do not appear in the net ionic equation.

Key Concepts

Bauxite

Bauxite is a term used to describe a mixture of minerals from which aluminum is extracted. Unlike a single mineral with a fixed chemical formula, bauxite comprises minerals like gibbsite, boehmite, and diaspore. Each of these contains aluminum in different forms.

This ore is mainly found in tropical and subtropical regions, making it a crucial resource for aluminum production worldwide. The process of extracting aluminum from bauxite involves several steps, including mining and refining through the Bayer process. This refining separates the valuable aluminum-containing minerals from other components. Bauxite is also a primary material for various chemical processes, which transform aluminum compounds into other useful materials.

Gibbsite

Gibbsite is one of the key minerals present in bauxite. Chemically, it is known as aluminum hydroxide with the formula \( ext{Al}( ext{OH})_{3}\). Being an important source of aluminum, gibbsite plays a significant role in the Bayer process, which is used to refine bauxite into alumina (aluminum oxide).

The presence of gibbsite in bauxite makes it reactive, particularly with acids, due to its hydroxide component. This reactivity means that it can dissolve in strong acids like sulfuric acid. In chemical reactions, gibbsite acts as a base because it can donate hydroxide ions when reacting with acids. Understanding these properties helps in predicting and balancing chemical reactions involving gibbsite.

Sulfuric Acid Reaction

The reaction of sulfuric acid with gibbsite is a classic example of an acid-base reaction. Sulfuric acid, \( ext{H}_2 ext{SO}_4\), is a strong acid that dissociates in solution to release 2 hydrogen ions \(2 ext{H}^+ \).

When sulfuric acid reacts with gibbsite, the hydrogen ions from the acid react with the hydroxide ions from gibbsite. This leads to the formation of water and aluminum sulfate. The chemical equation for this reaction can be written as:

\[ 2 ext{Al}( ext{OH})_3 (s) + 3 ext{H}_2 ext{SO}_4 (aq) \rightarrow ext{Al}_2( ext{SO}_4)_3 (aq) + 6 ext{H}_2 ext{O} (l) \]

This balanced equation shows the substances involved and the products formed, helping to visualize the changes happening at the molecular level.

Net Ionic Equation

While the overall equation provides a complete picture of the chemical reaction, the net ionic equation focuses only on the ions and molecules directly involved. It strips away the spectator ions that do not participate in the reaction itself.

For the reaction between gibbsite and sulfuric acid, the net ionic equation shows the essential transformation:

\[ 2 ext{Al}( ext{OH})_3(s) + 6 ext{H}^+(aq) \rightarrow 2 ext{Al}^{3+}(aq) + 6 ext{H}_2 ext{O}(l) \]

In this equation, you can see how 6 hydrogen ions and gibbsite react to produce aluminum ions and water. The sulfate ions (\(\text{SO}_4^{2-}\)), present in the overall equation as part of sulfuric acid, appear on both sides unchanged and are therefore omitted from the net ionic equation. This simplification helps focus on the core chemical process.