Molar Mass and the Mole (CHGM-141 Lecture 4b)

Vocabulary flashcards covering key concepts from the lecture notes on molar mass, the mole, Avogadro’s number, isotopes, and mass–amount conversions.

Mole

The amount of substance that contains as many particles (atoms, molecules, or formula units) as there are in 12.0 g of carbon-12; a counting unit used in chemistry.

Avogadro’s number

6.022 × 10^23 particles per mole; the number of constituent particles in one mole of any substance.

Molar mass

The mass in grams of one mole of a substance (elements or compounds).

Atomic weight

The numeric value equal to an element’s molar mass expressed in atomic mass units; the molar mass in g/mol is numerically equal to the atomic weight.

12C (carbon-12)

One mole of carbon-12 has a mass of 12.00 g and contains 6.022 × 10^23 atoms; the molar mass of carbon is 12.011 g/mol when isotopes are accounted for.

Isotopes

Atoms of the same element with different masses; molar mass is a weighted average of isotopes.

Molar mass units

Measured in grams per mole (g/mol).

Mass–to–particles connection

Avogadro’s number links macroscopic mass to microscopic particles; mass in grams relates to moles via molar mass.

Mole as a counting unit (analogy)

A mole counts particles the way a dozen counts eggs or a case counts beers—one mole equals 6.022 × 10^23 particles.

Mass–moles relationship

Mass (g) = moles × molar mass (g/mol); moles = mass (g) / molar mass (g/mol).

Lithium molar mass

6.941 g/mol.

Iron (Fe) molar mass

55.845 g/mol.

Example: 2.50 moles of Pb

Approximately 518 g of Pb (Pb molar mass ≈ 207.2 g/mol).

Elemental molar mass vs atomic weight

An element’s molar mass in g/mol is numerically equal to its atomic weight.