Problem 35 - Chemistry and Chemical Reactivity

Question

Complete and balance the equations for the following acid-base reactions. Name the reactants and products. (a) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\mathrm{aq})+\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s}) \rightarrow\) (b) \(\mathrm{HClO}_{4}(\mathrm{aq})+\mathrm{NH}_{3}(\mathrm{aq}) \rightarrow\)

Step-by-Step Solution

Answer

(a) Balanced: \(2\mathrm{CH}_3\mathrm{CO}_2\mathrm{H} + \mathrm{Mg(OH)}_2 \rightarrow \mathrm{Mg(CH}_3\mathrm{CO}_2)_2 + 2\mathrm{H}_2\mathrm{O}\). (b) Balanced: \(\mathrm{HClO}_4 + \mathrm{NH}_3 \rightarrow \mathrm{NH}_4\mathrm{ClO}_4\).

Step 1: Identify the Reaction Type for Equation (a)

The reaction between acetic acid \((\mathrm{CH}_3\mathrm{CO}_2\mathrm{H})\) and magnesium hydroxide \((\mathrm{Mg(OH)}_2)\) is a typical acid-base reaction where the acid reacts with a base to form salt and water.

Step 2: Write the Unbalanced Equation for (a)

Since acetic acid is a weak acid and \(\mathrm{Mg(OH)}_2\) is a base, the products are magnesium acetate and water:\[ \mathrm{CH}_3\mathrm{CO}_2\mathrm{H} + \mathrm{Mg(OH)}_2 \rightarrow \mathrm{Mg(CH}_3\mathrm{CO}_2)_2 + \mathrm{H}_2\mathrm{O} \]

Step 3: Balance the Reaction for Equation (a)

Balance the chemical equation by ensuring the same number of each type of atom on both sides. The balanced equation is:\[ 2\mathrm{CH}_3\mathrm{CO}_2\mathrm{H} + \mathrm{Mg(OH)}_2 \rightarrow \mathrm{Mg(CH}_3\mathrm{CO}_2)_2 + 2\mathrm{H}_2\mathrm{O} \]

Step 4: Name the Reactants and Products for (a)

Reactants: Acetic Acid \((\mathrm{CH}_3\mathrm{CO}_2\mathrm{H})\), Magnesium Hydroxide \((\mathrm{Mg(OH)}_2)\).Products: Magnesium Acetate \((\mathrm{Mg(CH}_3\mathrm{CO}_2)_2)\), Water \((\mathrm{H}_2\mathrm{O})\).

Step 5: Identify the Reaction Type for Equation (b)

The reaction between perchloric acid \((\mathrm{HClO}_4)\) and ammonia \((\mathrm{NH}_3)\) is an acid-base reaction leading to the formation of a salt.

Step 6: Write the Unbalanced Equation for (b)

Perchloric acid reacts with ammonia to form ammonium perchlorate:\[ \mathrm{HClO}_4 + \mathrm{NH}_3 \rightarrow \mathrm{NH}_4\mathrm{ClO}_4 \]

Step 7: Balance the Reaction for Equation (b)

The equation is already balanced:\[ \mathrm{HClO}_4 + \mathrm{NH}_3 \rightarrow \mathrm{NH}_4\mathrm{ClO}_4 \]

Step 8: Name the Reactants and Products for (b)

Reactants: Perchloric Acid \((\mathrm{HClO}_4)\), Ammonia \((\mathrm{NH}_3)\).Product: Ammonium Perchlorate \((\mathrm{NH}_4\mathrm{ClO}_4)\).

Key Concepts

Chemical Equation Balancing

Balancing chemical equations is a fundamental skill in chemistry. It ensures that the same number of atoms of each element is present on both sides of the equation. This reflects the conservation of mass during chemical reactions. In the given exercise, for acetic acid reacting with magnesium hydroxide, the unbalanced equation is:\[ \mathrm{CH}_3\mathrm{CO}_2\mathrm{H} + \mathrm{Mg(OH)}_2 \rightarrow \mathrm{Mg(CH}_3\mathrm{CO}_2)_2 + \mathrm{H}_2\mathrm{O} \]To balance this equation, observe the number of each type of atom. Acetic acid has one acetic group, but you need two to balance with the magnesium acetate formed. Thus, using two molecules of acetic acid balances the acetate ions. Water molecules are also balanced by ensuring that two water molecules are formed. The balanced chemical equation becomes:\[ 2\mathrm{CH}_3\mathrm{CO}_2\mathrm{H} + \mathrm{Mg(OH)}_2 \rightarrow \mathrm{Mg(CH}_3\mathrm{CO}_2)_2 + 2\mathrm{H}_2\mathrm{O} \]Remember, balancing equations does not change the compounds; it only ensures that each type of atom has the same total count before and after the reaction, reflecting the law of conservation of mass.

Acetic Acid Reactions

Acetic acid, known chemically as \(\mathrm{CH}_3\mathrm{CO}_2\mathrm{H}\), is a weak acid that participates in reactions similar to those of other acids. In an acid-base reaction, acetic acid typically donates protons to the base. Here, it reacts with magnesium hydroxide \((\mathrm{Mg(OH)}_2)\), a base, to form magnesium acetate and water.

• The energy change involved in this reaction results in the formation of salt and water, a classic neutralization reaction.
• Being a weak acid, acetic acid does not completely ionize in water, distinguishing its reactions somewhat from those of strong acids like hydrochloric acid.

Magnesium acetate formed in this reaction is a salt that is often used in chemical synthesis and industrial applications. The reaction between acetic acid and magnesium hydroxide can be represented, as we balanced earlier, showing the transformation of reactants to products with distinct properties.

Perchloric Acid Reactions

Perchloric acid, \(\mathrm{HClO}_4\), is a strong acid and exhibits vigorous reactions, especially in acid-base interactions. In the problem presented, it reacts with ammonia \((\mathrm{NH}_3)\), a common base, resulting in the formation of a salt, ammonium perchlorate. The balanced chemical equation for this reaction is straightforward:\[ \mathrm{HClO}_4 + \mathrm{NH}_3 \rightarrow \mathrm{NH}_4\mathrm{ClO}_4 \]

• Perchloric acid fully dissociates in solution, making it very reactive compared to weak acids.
• This reaction is an example of a neutralization reaction where acid molecules donate protons to the basic ammonia molecules.

Ammonium perchlorate formed in the reaction is notable for its use in solid rocket fuel. The balancing of this acid-base reaction demonstrates the straightforward stoichiometric relationship typical of strong acids reacting with bases, as seen here where each reactant transforms cleanly into product without the need for additional balancing steps.