Problem 27 - General Chemistry: Principles and Modern Applications

Question

Write chemical equations to represent the (a) reaction of \(\mathrm{Al}(\mathrm{s})\) with \(\mathrm{HCl}(\mathrm{aq})\) (b) reaction of \(\mathrm{Al}(\mathrm{s})\) with \(\mathrm{NaOH}(\mathrm{aq})\) (c) oxidation of \(\mathrm{Al}(\mathrm{s})\) to \(\mathrm{Al}^{3+}(\) aq) by an aqueous solution of sulfuric acid; the reduction product is \(\mathrm{SO}_{2}(\mathrm{g}).\)

Step-by-Step Solution

Answer

(a) \( \mathrm{Al}(\mathrm{s}) + 3\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{AlCl}_{3}(\mathrm{aq}) + 3\mathrm{H}_{2}(\mathrm{g}) \) (b) \( \mathrm{Al}(\mathrm{s}) + 3\mathrm{NaOH}(\mathrm{aq}) \rightarrow 2\mathrm{NaAlO}_{2}(\mathrm{aq}) + 3\mathrm{H}_{2}(\mathrm{g}) \) (c) \(2\mathrm{Al}(\mathrm{s}) + 3\mathrm{H}_{2}\mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Al}_{2}(\mathrm{SO}_4)_{3}(\mathrm{aq}) + 3\mathrm{SO}_2(\mathrm{g}) + 3\mathrm{H}_2\mathrm{O}(\mathrm{l})\)

Step 1: Reaction of Al(s) with HCl(aq)

When aluminum reacts with Hydrochloric acid, aluminum chloride and hydrogen gas are produced. The unbalanced chemical reaction is: \(\mathrm{Al}(\mathrm{s}) + \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{AlCl}_{3}(\mathrm{aq}) + \mathrm{H}_{2}(\mathrm{g})\). To balance this reaction, it's necessary to add '3' as the coefficient of \(\mathrm{HCl}\) and \(\mathrm{H}_{2}\) on each side of the reaction: \( \mathrm{Al}(\mathrm{s}) + 3\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{AlCl}_{3}(\mathrm{aq}) + 3\mathrm{H}_{2}(\mathrm{g}) \)

Step 2: Reaction of Al(s) with NaOH(aq)

When aluminum reacts with Sodium hydroxide, sodium aluminate and hydrogen gas are produced. The unbalanced chemical reaction is: \(\mathrm{Al}(\mathrm{s}) + \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{NaAlO}_{2}(\mathrm{aq}) + \mathrm{H}_{2}(\mathrm{g})\). To balance this reaction, it's necessary to add '3' as the coefficient of \(\mathrm{NaOH}\) and \(\mathrm{H}_{2}\), and '2' as the coefficient of \(\mathrm{NaAlO}_{2}\) on each side of the reaction: \( \mathrm{Al}(\mathrm{s}) + 3\mathrm{NaOH}(\mathrm{aq}) \rightarrow 2\mathrm{NaAlO}_{2}(\mathrm{aq}) + 3\mathrm{H}_{2}(\mathrm{g}) \)

Step 3: Oxidation of Al(s) to Al3+(aq) by H2SO4(aq)

When aluminum is oxidized by sulfuric acid, Aluminum sulfate, sulfur dioxide and water are formed. The unbalanced chemical reaction is: \(\mathrm{Al}(\mathrm{s}) + \mathrm{H}_{2}\mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Al}_{2}(\mathrm{SO}_4)_{3}(\mathrm{aq}) + \mathrm{SO}_2(\mathrm{g}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\). To balance this reaction, use '2' as coefficient of \(\mathrm{Al}\), '3' for \(\mathrm{H}_{2}\mathrm{SO}_{4}\) and \(\mathrm{H}_2\mathrm{O}\): \(2\mathrm{Al}(\mathrm{s}) + 3\mathrm{H}_{2}\mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Al}_{2}(\mathrm{SO}_4)_{3}(\mathrm{aq}) + 3\mathrm{SO}_2(\mathrm{g}) + 3\mathrm{H}_2\mathrm{O}(\mathrm{l})\)

Key Concepts

Balancing Chemical Equations

In order to understand how substances react in a chemical reaction, it's crucial to write and balance chemical equations. A chemical equation describes the conversion of reactants into products. It uses symbols and formulas to represent the substances involved. The process of balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation. This is important because according to the Law of Conservation of Mass, matter cannot be created or destroyed in a chemical reaction, only rearranged.

• Identify the reactants and products: write their chemical formulas correctly.
• Count the number of atoms of each element in the reactant side and compare with the product side.
• Use coefficients to balance the atoms in each element across the equation. Start with the most complex substance.
• Always double-check to ensure that all elements are balanced.

Balancing equations can sometimes be tricky. Practice helps in understanding the relationship between reactants and products and predicting possible outcomes of a chemical reaction.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, often referred to as redox reactions, are a type of chemical reaction where electrons are transferred between two substances. These reactions are characterized by changes in oxidation states and are essential in various chemical processes.

In a redox reaction, one substance loses electrons and becomes oxidized, while the other gains electrons and becomes reduced. The substance that donates electrons is called the reducing agent, and the one that accepts electrons is the oxidizing agent. In the context of aluminum reactions, consider the oxidation of aluminum metal:

• Aluminum (\[ ext{Al(s)}\]) is oxidized to aluminum ions (\[ ext{Al}^{3+} ext{ (aq)}\]) by losing electrons.
• The corresponding reduction might involve the conversion of sulfuric acid into sulfur dioxide, where sulfur gains the electrons lost by aluminum.

Understanding redox reactions is important not only to predict chemical changes but also in real-world applications like corrosion, batteries, and metabolic processes.

Aluminum and Acids Reactions

Aluminum is a lightweight metal that is highly reactive with acids such as hydrochloric acid (\[ ext{HCl} ext{ (aq)}\]) and sulfuric acid (\[ ext{H}_2 ext{SO}_4 ext{ (aq)}\]). When aluminum reacts with these acids, products such as aluminum salts and hydrogen gas are typically formed:

• When reacting with hydrochloric acid:
  \[ ext{Al(s) + 3HCl(aq)} ightarrow ext{AlCl}_3 ext{(aq) + 3H}_2 ext{(g)}\]
  Here, aluminum chloride and hydrogen gas are produced.
• Reactions with sulfuric acid:
  \[2 ext{Al(s) + 3H}_2 ext{SO}_4 ext{ (aq)} ightarrow ext{Al}_2 ext{(SO}_4)_3 ext{(aq) + 3SO}_2 ext{(g) + 3H}_2 ext{O(l)}\]
  Aluminum sulfate, sulfur dioxide, and water are formed.

These reactions involve the formation of gas, which can be observed as bubbles escaping from the reaction mixture. Understanding these reactions can provide insight into manipulating various parameters in chemical industries and processes.

Chemical Equations

Chemical equations serve as a universal language for chemists, enabling them to describe chemical reactions succinctly. An equation clearly conveys what substances react, on the left side, and what new substances form, on the right side.

Here's how to understand and write chemical equations:

• Identify the reactants, the starting substances in the reaction.
• Identify the products, the substances formed as a result of the reaction.
• Use proper chemical symbols and states, such as (s) for solid, (aq) for aqueous or dissolved in water, (g) for gas, and (l) for liquid.
• A plus sign separates multiple reactants or products, while an arrow shows the direction from reactants to products.

For example, the balanced equation for aluminum reacting with hydrochloric acid is written as:
\[ ext{Al(s) + 3HCl(aq)} ightarrow ext{AlCl}_3 ext{(aq) + 3H}_2 ext{(g)}\]
This represents how reactants interact and transform into new substances, allowing for prediction and analysis of chemical behavior.