Problem 19 - Chemistry and Chemical Reactivity

Question

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

Step-by-Step Solution

Answer

(a) Products: magnesium acetate and water. (b) Product: ammonium perchlorate.

Step 1: Identify the Reactants

In reaction (a), the reactants are acetic acid, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}(\mathrm{aq})\), and magnesium hydroxide, \(\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})\). Acetic acid is a weak acid, and magnesium hydroxide is a base.In reaction (b), the reactants are perchloric acid, \(\mathrm{HClO}_{4}(\mathrm{aq})\), and ammonia, \(\mathrm{NH}_{3}(\mathrm{aq})\). Perchloric acid is a strong acid, and ammonia is a weak base.

Step 2: Predict the Major Products

In reaction (a), when an acid reacts with a base, the typical products are a salt and water. The salt formed will be magnesium acetate, \(\mathrm{Mg}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2\), and water, \(\mathrm{H}_2\mathrm{O}\).In reaction (b), the acid \(\mathrm{HClO}_4\) will donate a proton to the base \(\mathrm{NH}_3\), resulting in ammonium perchlorate, \(\mathrm{NH}_4\mathrm{ClO}_4\).

Step 3: Write the Balanced Chemical Equations

For reaction (a):1. The balanced equation is: \[ 2 \mathrm{CH}_3\mathrm{CO}_2\mathrm{H}(\mathrm{aq}) + \mathrm{Mg}(\mathrm{OH})_2(\mathrm{s}) \rightarrow \mathrm{Mg}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2(\mathrm{aq}) + 2\mathrm{H}_2\mathrm{O}(\mathrm{l}) \] Each side of the equation contains two acetate ions, one magnesium ion, and two water molecules.2. The names of the products are magnesium acetate and water.For reaction (b):1. The balanced equation is: \[ \mathrm{HClO}_4(\mathrm{aq}) + \mathrm{NH}_3(\mathrm{aq}) \rightarrow \mathrm{NH}_4\mathrm{ClO}_4(\mathrm{aq}) \] Each side has one chlorine, one nitrogen, and four oxygen atoms.2. The name of the product is ammonium perchlorate.

Step 4: Verify the Balancing and Naming

Check that the number of each type of atom on both sides of each equation is balanced, and that the names of the compounds are correct. For reaction (a), \(\mathrm{Mg}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2\) is magnesium acetate, and it is properly balanced in the equation with water.For reaction (b), \(\mathrm{NH}_4\mathrm{ClO}_4\) is ammonium perchlorate, and the equation is already balanced.

Key Concepts

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show how reactants transform into products. In the world of chemistry, reactants are the starting substances, while products are the substances that form as a result of the reaction. For an acid-base reaction like the one in our example, the equation indicates the neutralization process that occurs when an acid reacts with a base. To construct a chemical equation:

• Write down the formulas of the reactants.
• Draw an arrow pointing towards the products, indicating the direction of the reaction.
• Write down the formulas of the products.

In reaction (a), the reactants are acetic acid ( CH_{3}CO_{2}H ) and magnesium hydroxide ( Mg(OH)_{2} ), leading to the formation of magnesium acetate and water.

Reaction Balancing

Reaction balancing is a fundamental part of writing chemical equations. It ensures that the same number of each type of atom appears on both sides of the equation. This honoring of the Law of Conservation of Mass is crucial in chemistry. Let's look at reaction (a) from the original problem:

• The balanced chemical equation is: \[2 \mathrm{CH}_3\mathrm{CO}_2\mathrm{H}(\mathrm{aq}) + \mathrm{Mg}(\mathrm{OH})_2(\mathrm{s}) \rightarrow \mathrm{Mg}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2(\mathrm{aq}) + 2\mathrm{H}_2\mathrm{O}(\mathrm{l}) \]
• This equation is balanced because there are equal numbers of each type of atom on both sides:
• Four hydrogen atoms from acetic acid and four from water.
• Two oxygen atoms from the hydroxide and two from water.
• One magnesium ion and four carbons from the acetate.

Balancing these equations can require practice and careful attention to detail.

Product Naming

Product naming in chemistry follows specific patterns based on the compounds formed. Once the chemical equation is formulated and balanced, naming the products correctly is essential. In acid-base reactions:

• A salt is commonly one of the products.
• The formation of water is another common product through this neutralization process.

In reaction (a), magnesium acetate is the salt formed when acetic acid and magnesium hydroxide react. As for the products in these equations:

• Magnesium acetate comes from the acetate ion and magnesium cation.
• Water is the simplest molecule, composed of two hydrogen atoms and one oxygen atom.

Using systematic naming helps chemists and students communicate clearly about chemical substances.

Acetic Acid

Acetic acid is a weak acid found in many households as vinegar's key component. In chemical terms, it is written as CH_{3}CO_{2}H , where the acetate group is C_{2}H_{3}O_{2}^{-} . For acid-base reactions, acetic acid acts as the proton donor, engaging with bases to form salts and water. Some properties of acetic acid include:

• Familiar sour taste and pungent smell.
• It is a colorless liquid when pure.

In the context of our chemical equation, acetic acid combines with magnesium hydroxide, producing magnesium acetate and water through a neutralization reaction.

Magnesium Hydroxide

Magnesium hydroxide is a base, recognized in chemistry by the formula Mg(OH)_{2} . It is commonly found in antacids and laxatives for its ability to neutralize acidity. When magnesium hydroxide encounters an acid, it reacts to form a salt and water. Here are some features of magnesium hydroxide:

• It appears as a white solid and is only slightly soluble in water.
• It acts as a source of OH^{-} ions in chemical reactions.

In the example reaction, magnesium hydroxide reacts with acetic acid to form magnesium acetate and water. Its role as a base is fundamental, as it provides the OH^{-} necessary for the formation of water during the reaction.