Question

Explain the important distinctions between each pair of terms: (a) molecular mass and molar mass; (b) empirical and molecular formulas; (c) systematic and trivial, or common, name; (d) hydroxyl and carboxyl functional group.

Short answer

Molecular mass is the mass of a single molecule, while molar mass is the mass of a mole of a substance, expressed in g/mol. Empirical formulas show the simplest whole number ratio of atoms, while molecular formulas show the actual number of atoms in a molecule. Systematic names follow specific rules established by IUPAC, while trivial names are common names that are not universal. Hydroxyl group is an oxygen and hydrogen atom bonded together, while carboxyl group involves a carbon atom double-bonded to an oxygen and single bonded to a hydroxyl group, forming a carboxylic acid.

Step-by-step solution

Distinguishing Molecular Mass and Molar Mass

Molecular mass refers to the mass of a single molecule, usually expressed in atomic mass units (u). It is calculated as the sum of the atomic masses of each atom in a molecule. In comparison, molar mass is the mass of one mole (6.02 x \(10^{23}\) entities) of a substance. It is expressed in grams per mole (g/mol) and is equivalent to the molecular mass for a substance but expressed in different units. Also, while molecular mass is useful in understanding the properties of individual molecules, molar mass allows chemists to track the amounts and transformations of substances in chemical reactions.

Distinguishing Empirical and Molecular Formulas

Empirical and molecular formulas represent the types and quantities of atoms in a compound. The empirical formula shows the simplest whole number ratio of the atoms, while the molecular formula shows the actual number of each type of atom in a molecule of the compound. Therefore, multiple compounds can share the same empirical formula, but each compound will have a unique molecular formula.

Distinguishing Systematic and Trivial (common) Name

A systematic (or IUPAC) name for a compound follows specific rules established by the International Union of Pure and Applied Chemistry (IUPAC). This name ensures consistent naming across different platforms and languages. In contrast, a trivial or common name is often used for simplicity and ease, but may not provide information about the compound's structure and is not universal. For example, the systematic name for vinegar is acetic acid, which highlights its carboxyl functional group.

Distinguishing Hydroxyl and Carboxyl Functional Group

A hydroxyl group consists of an oxygen atom bonded to a hydrogen atom (-OH) while a carboxyl group involves a carbon atom double-bonded to an oxygen atom and single bonded to a hydroxyl group (-COOH). A compound with a hydroxyl group is an alcohol, but if it has a carboxyl group, it is a carboxylic acid. The presence of these functional groups determines the behavior and reactions of the molecule they're part of.

Key concepts

Molecular Mass vs Molar Mass

Understanding the difference between molecular mass and molar mass is crucial in chemistry. Molecular mass refers to the mass of a single molecule of a substance, calculated by summing the atomic masses of its constituent atoms, and it is usually measured in atomic mass units (u). This is handy when studying the properties of individual molecules.
In contrast, molar mass is the mass of one mole of a substance, where one mole corresponds to Avogadro's number, which is approximately 6.02 x \(10^{23}\) entities. Molar mass is measured in grams per mole (g/mol), and it reflects how the substance behaves in larger quantities, such as in chemical reactions. While these terms describe similar concepts, their application varies significantly based on the context—molecular mass is for the microscopic scale, and molar mass is for the macroscopic scale.

Empirical vs Molecular Formulas

Empirical and molecular formulas provide different types of information about the composition of a compound. An empirical formula gives the simplest whole number ratio of the types of atoms in a compound. For example, the empirical formula for glucose is \(\text{{CH}}_2\text{{O}}\).
On the other hand, a molecular formula provides the exact number of each type of atom present in a single molecule of the compound. The molecular formula for glucose is \(\text{{C}}_6\text{{H}}_{12}\text{{O}}_6\). This distinction is essential because while multiple compounds can share the same empirical formula, each will have a unique molecular formula. The molecular formula shows the actual structure and composition of the molecule, which is crucial for determining its properties and behavior.

Systematic vs Trivial Names

When naming chemical compounds, systematic and trivial names offer different benefits. Systematic names, often referred to as IUPAC names, follow the rigorous nomenclature rules set by the International Union of Pure and Applied Chemistry. These names are consistent and precise, allowing scientists from different regions and languages to understand each other without confusion. For example, ethanol can be named systematically as \(\text{{C}}_2\text{{H}}_5\text{{OH}}\).
Trivial names (or common names), however, are often derived from historical naming and can be simpler, making them easier to remember and use in everyday conversation. These names do not always reflect the chemical structure, like how acetic acid commonly refers to vinegar, focusing more on practicality. While they are more accessible, trivial names lack the specific structural information contained in systematic names.

Hydroxyl vs Carboxyl Functional Groups

Functional groups in organic chemistry are critical as they define the properties and reactions of compounds. The hydroxyl group, represented as \(-\text{OH}\), features an oxygen atom bonded to a hydrogen atom. It is the defining feature of alcohols, such as ethanol. The presence of a hydroxyl group typically makes the compound more soluble in water and can participate in hydrogen bonding.
In comparison, the carboxyl group, shown as \(-\text{COOH}\), combines a carbon double-bonded to an oxygen with a hydroxyl group. This group is characteristic of carboxylic acids like acetic acid. Carboxyl groups are known for their acidity since they can donate a hydrogen ion (\(\text{H}^+\)) in solution, contributing to their unique reactivity. These specific functional groups play vital roles in defining the chemical nature and reactivity of the molecules they reside in.