Question

The formula for acetic acid, the acid present in vinegar, is commonly written as \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\). Many chemists write the formula as \(\mathrm{CH}_{3} \mathrm{COOH}\). a. Draw the Lewis structure for acetic acid. b. Show that both formulas represent acetic acid. c. What are the advantages and disadvantages of each formula? d. How many hydrogen atoms can be released as hydrogen ions per acetic acid molecule? Explain.

Short answer

Both formulas represent acetic acid structurally and compositionally accurate; one hydrogen ion can be released per molecule.

Step-by-step solution

Understanding Sepcial Formula Representation

Acetic acid can be represented by two different chemical formulas, \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) and \(\mathrm{CH}_{3} \mathrm{COOH}\). These formulas signify the contents but may hint at different structural layouts. Let's draw its Lewis structure to visually represent the molecule.

Drawing the Lewis Structure of Acetic Acid

The Lewis structure illustrates the atoms' arrangement and bonding in a molecule. In acetic acid, \(\mathrm{CH}_{3}\) is bonded to \(\mathrm{COOH}\). Draw the methyl group \(\mathrm{CH}_{3}\), then connect it to the carboxyl group, \(\mathrm{COOH}\). In the carboxyl group, one oxygen atom is double-bonded to carbon, while the other oxygen has a single bond with carbon and an additional hydrogen atom.

Verifying Structural Representations

The molecular composition remains the same for both formulas as both show that acetic acid consists of two carbon atoms, four hydrogen atoms, and two oxygen atoms. This equivalence confirms that \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) is essentially \(\mathrm{CH}_{3} \mathrm{COOH}\), only arranged differently position-wise.

Considering Formula Advantages and Disadvantages

The formula \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) reflects the atomic composition of acetic acid clearly, which is advantageous for quick recognition of elements in the compound. In contrast, \(\mathrm{CH}_{3} \mathrm{COOH}\) reveals both atomic composition and provides insight into its functional groups' structure, allowing better understanding of its chemistry, such as its acidic nature.

Assessing Hydrogen Ion (H⁺) Release Potential

In the carboxyl group \(\mathrm{COOH}\), hydrogen can dissociate to form \(\mathrm{H}^+\) ions. Therefore, one hydrogen atom (from the \(\mathrm{COOH}\) group) is available to be released as a hydrogen ion, enabling the molecule to act as an acid. Though there are more hydrogens, only one impacts acidity.

Key concepts

Lewis Structure

A Lewis structure is a visual representation of the bonds formed between atoms within a molecule. It shows the molecule's atoms and indicates the bonds between them as well as any lone pairs of electrons. For acetic acid, drawing its Lewis structure helps us to understand how its atoms are arranged.

Acetic acid has the formula \( \mathrm{CH}_{3} \mathrm{COOH} \). It consists of two main parts: a methyl group \( \mathrm{CH}_{3} \), and a carboxyl group \( \mathrm{COOH} \).

To construct the Lewis structure:

• Start with the \( \mathrm{CH}_3 \) group, which indicates three hydrogen atoms bonded to a carbon atom.
• The carbon of \( \mathrm{CH}_3 \) is connected to another carbon which forms part of the \( \mathrm{COOH} \) group.
• In the carboxyl group, one oxygen is double-bonded to the carbon, while the second oxygen single bonds with the carbon and carries an additional hydrogen atom.

Understanding and drawing the Lewis structure allows chemists to visualize how bonds form and where lone electrons might exist.

Molecular Formula

The molecular formula of a compound informs us of the actual number and variety of atoms present in a molecule. For acetic acid, chemists can use two different molecular formulas: \( \mathrm{HC}_2 \mathrm{H}_3 \mathrm{O}_2 \) and \( \mathrm{CH}_3 \mathrm{COOH} \).

While both represent the same compound, their differences lie in how they portray the structure of the molecule:

• \( \mathrm{HC}_2 \mathrm{H}_3 \mathrm{O}_2 \) - This formula emphasizes the atomic composition without providing structural insight.
• \( \mathrm{CH}_3 \mathrm{COOH} \) - This version makes it easy to understand that acetic acid includes functional groups due to its pattern, directly showing the carboxyl and methyl groups.

The ability to discern between these formats gives better clarity about both elemental composition and potential chemical behavior.

Functional Groups

Functional groups are specific clusters of atoms within molecules that have distinct patterns and chemical behaviors. In organic chemistry, these groups are crucial as they define the characteristics and reactivity of a compound.

In the case of acetic acid, the notable functional group is the carboxyl group \( \mathrm{COOH} \). This group consists of a carbon double-bonded to an oxygen, and also single-bonded to another oxygen carrying a hydrogen atom. This structure characterizes acetic acid as an acid:

• The \( \mathrm{OH} \) part of the group can dissociate, releasing a \( \mathrm{H}^+ \) ion.
• Understanding this functional group is essential for predicting how acetic acid will react, especially in its ability to donate a proton, identifying it as an acid.

Such functional groups are the foundation of a molecule’s identity and are responsible for particular properties.

Hydrogen Ion Release

Acetic acid is characterized by its ability to release hydrogen ions (\( \mathrm{H}^+ \)) when dissolved in water, showcasing its acidic nature. This behavior is predominantly influenced by its carboxyl group (\( \mathrm{COOH} \)).

Here's how hydrogen ion release occurs:

• The \( \mathrm{COOH} \) group in acetic acid contains a hydrogen atom bonded to an oxygen atom.
• This hydrogen can dissociate from the \( \mathrm{OH} \) to form a \( \mathrm{H}^+ \) ion.
• When the \( \mathrm{H}^+ \) ion is released, acetic acid donates a proton, thus acting as an acid.

Although acetic acid contains more hydrogen atoms, only one in the carboxyl group is responsible for the acidic property of the molecule. Understanding this concept helps students grasp why acetic acid can be utilized in various acid-base reactions.