Problem 104 - Chemistry Matter and Change

Question

Which has more mass, a mole of potassium or a mole of sodium? Explain your answer.

Step-by-Step Solution

Answer

A mole of potassium has more mass than a mole of sodium.

Step 1: Understanding the Mole Concept

A mole is a unit in chemistry that represents a specific number of particles, atoms, or molecules, typically Avogadro's number, which is approximately \(6.022 \times 10^{23}\). In this problem, we're comparing one mole of potassium atoms to one mole of sodium atoms.

Step 2: Periodic Table Look-Up

To find the molar mass of sodium (Na) and potassium (K), look them up on the periodic table. The molar mass of sodium is approximately 22.99 g/mol, while the molar mass of potassium is approximately 39.10 g/mol.

Step 3: Comparison of Molar Masses

Now compare the two molar masses: Sodium has a molar mass of 22.99 g/mol and potassium has a molar mass of 39.10 g/mol. This means that one mole of potassium atoms has more mass than one mole of sodium atoms.

Key Concepts

Mole Concept

The mole concept is a fundamental principle in chemistry that simplifies the study of substances by relating large quantities of atoms or molecules to a single unit. One mole is defined as exactly 6.022 x 10^{23} particles, be it atoms, molecules, ions, or electrons. This number, known as Avogadro's number, serves as a bridge between the atomic scale and the macroscopic scale, allowing chemists to quantify and comprehend chemical quantities easily.
For example, when chemists say they have a mole of a substance, they're referring to 6.022 x 10^{23} of that substance's fundamental units. Understanding moles is crucial for calculating the amount of substances involved in chemical reactions, as it allows scientists to accurately measure reactants and products in a controlled and meaningful way.

Molar Mass

Molar mass is an essential concept that relates the mass of a substance to the number of moles. It represents the mass of one mole of a given substance and is expressed in grams per mole (g/mol). To determine the molar mass of an element, simply locate the atomic weight on the periodic table.

• The atomic weight of an element corresponds to its molar mass in g/mol.
• For compounds, molar mass is calculated by summing the molar masses of all constituent elements.

In the context of the given exercise, potassium (K) has a molar mass of approximately 39.10 g/mol, while sodium (Na) has a molar mass of approximately 22.99 g/mol. This calculation helps us understand that a mole of potassium is heavier than a mole of sodium.

Periodic Table

The periodic table is a comprehensive chart that organizes all known elements by increasing atomic number and groups them into categories based on similar properties. It acts as a reference tool for chemists when determining elemental properties, such as atomic number, electron configuration, and atomic weight.
For the exercise of comparing moles of potassium and sodium, the periodic table becomes particularly useful. By examining this chart, one can easily find:

• Potassium occupies group 1 and has an atomic weight corresponding to 39.10 g/mol.
• Sodium, also in group 1, has an atomic weight of approximately 22.99 g/mol.

The periodic table empowers chemists with valuable information that aids in the understanding of interactions, reactions, and relationships between different elements.

Avogadro's Number

Avogadro's number is critical for converting between atomic scale measurements and practical laboratory quantities. It defines how many particles are in one mole of a substance: precisely 6.022 x 10^{23}. This large figure is essential since atoms and molecules are extremely small and not feasible to count individually.

• By using Avogadro's number, scientists can convert from moles to particles, and vice versa.
• It applies universally, regardless of the type of substance, ensuring uniformity in chemical calculations.

In essence, the comparison of moles of potassium and sodium demonstrates Avogadro's number's practical use: both moles contain exactly the same number of atoms, allowing the direct comparison of their masses, achieved through their respective molar masses.