Question

Write equations for the following reactions, representing the reactants and products using structural formulas. (a) The reaction of acetic acid and sodium hydroxide (b) The reaction of methylamine with \(\mathrm{HCl}\)

Short answer

(a) \( CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O \); (b) \( CH_3NH_2 + HCl \rightarrow CH_3NH_3Cl \).

Step-by-step solution

Identify the Reactants and Products for Reaction (a)

The reaction of acetic acid with sodium hydroxide is an acid-base neutralization reaction. Acetic acid is represented by the structural formula \( CH_3COOH \), and sodium hydroxide is represented by \( NaOH \). The products are water \( H_2O \) and sodium acetate \( CH_3COONa \).

Write the Balanced Equation for Reaction (a)

For the reaction of acetic acid and sodium hydroxide, write down the balanced chemical equation using their structural formulas. \[ CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O \]

Identify the Reactants and Products for Reaction (b)

The reaction involves methylamine and hydrochloric acid (\( HCl \)). Methylamine is represented by \( CH_3NH_2 \), and \( HCl \) is represented as \( HCl \). The product of this reaction is methylammonium chloride \( CH_3NH_3Cl \).

Write the Balanced Equation for Reaction (b)

For the reaction of methylamine with \( HCl \), write the balanced equation with structural formulas. \[ CH_3NH_2 + HCl \rightarrow CH_3NH_3Cl \]

Verify the Equations for Completeness and Balance

Ensure that all atoms and charges are balanced in both equations. Both reactions should follow the conservation of mass and charge.

Key concepts

Acid-Base Neutralization

Neutralization reactions are fascinating processes where an acid and a base react to form water and a salt. These reactions are pivotal in chemistry, playing significant roles in various applications.
For example, when acetic acid \(CH_3COOH\) reacts with sodium hydroxide \(NaOH\), it forms water \(H_2O\) and sodium acetate \(CH_3COONa\).
Methylamine \(CH_3NH_2\), a weak base, reacts with hydrochloric acid \(HCl\) to create methylammonium chloride \(CH_3NH_3Cl\).

• **Acids** donate protons \(H^+\) during the reaction.
• **Bases** accept protons \(H^+\).
• **Water** is frequently formed as a by-product.
• The salt forms from the unreacted ions left behind.

Managing pH levels in various environments relies heavily on neutralization reactions. From daily life in personal care products to large-scale industrial processes, these reactions are essential.

Structural Formulas

To fully understand chemical reactions, it's crucial to visualize how the atoms and molecules are rearranged. This is where structural formulas become extremely helpful.
Structural formulas provide insightful information about the arrangement of atoms within a molecule, which plain molecular formulas may not reveal.

• For acetic acid, its formula is \(CH_3COOH\), clearly illustrating the carboxyl group \(COOH\).
• Sodium hydroxide is shown as \(NaOH\), emphasizing the hydroxide group \(OH^-\).
• Methylamine, \(CH_3NH_2\), indicates the presence of an amino group.
• Hydrochloric acid \(HCl\) is straightforward, indicating a simple diatomic molecule.

These visual representations help you grasp how each atom connects and how they change during reactions. Understanding the structural makeup of reactants can clarify why specific products form.

Balanced Chemical Equations

Writing balanced chemical equations is a crucial skill in chemistry that represents a chemical reaction in a concise way.
A balanced equation ensures that the mass and atoms are the same on both sides, accurately reflecting the conservation of matter.
In the case of the reaction between acetic acid and sodium hydroxide:

• The equation is \[ CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O \]
• All atoms of carbon, hydrogen, oxygen, and sodium are accounted for equally on both sides.

Similarly, for methylamine reacting with hydrochloric acid:

• The balanced equation becomes \[ CH_3NH_2 + HCl \rightarrow CH_3NH_3Cl \]
• This confirms each atom involved, from methylamine attaches to form the ammonium chloride.

Balancing equations ensures that no atoms are lost or gained in the reaction, adhering to the laws of conservation. Proper balancing is vital for understanding and predicting chemical reactions accurately.

Conservation of Mass and Charge

In chemistry, the principle of conservation of mass and charge is foundational. It states that mass and charge are neither created nor destroyed in a chemical reaction.
This concept is particularly useful for correctly writing and balancing chemical equations.

• **Mass Conservation**: Each atom that enters a reaction must be accounted for in the products.
• In the acetic acid and sodium hydroxide reaction, the transition from reactants to products respects this principle beautifully.

For the reaction \(CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O\), every element on the reactant side is present in the products. The same applies to methylamine reacting with hydrochloric acid \(CH_3NH_2 + HCl \rightarrow CH_3NH_3Cl\).

• **Charge Conservation**: The total charge on each side of the equation must be equal.
• For example, the overall charge balance in methylamine's reaction with \(HCl\) showcases this perfectly.

Understanding these rules helps chemists ensure accurate representations of chemical reactions, vital for experimental precision and predictability.