Why is the mole used as a unit in chemistry?

• A. It provides a way to compare the densities of different substances.
• B. It measures the volume of gases at standard temperature and pressure.
• C. It is used to determine the color of chemical compounds.
• D. It allows chemists to count atoms, molecules, or ions by relating mass to number of particles.

Answer: (D)

Verified step by step guidance

1. Understand that atoms, molecules, and ions are extremely small and numerous, making it impractical to count them individually in a sample.
2. Recognize that the mole is a unit that relates the mass of a substance to the number of particles it contains, providing a bridge between the microscopic scale (atoms/molecules) and the macroscopic scale (grams).
3. Know that one mole corresponds to Avogadro's number, which is approximately \$6.022 \times 10^{23}$ particles, allowing chemists to count particles by weighing substances.
4. Realize that using the mole enables chemists to perform calculations involving chemical reactions, stoichiometry, and concentrations by converting between mass and number of particles.
5. Conclude that the mole is essential because it standardizes the counting of particles in chemistry, unlike units that measure volume, density, or color.