Algonquin College Health Program Assessment (AC-HPAT) Practice Exam

True or False: An element's molar mass and atomic weight are always equal.

1. True

2. False

3. It depends on the element

4. True only for metals

The correct answer is: False

The statement that an element's molar mass and atomic weight are always equal is false. While molar mass and atomic weight are closely related concepts, they are not identical. Atomic weight is a weighted average that accounts for the isotopes of an element as they occur in nature, measured in atomic mass units (amu). Since most elements exist as a mixture of isotopes, the atomic weight will vary based on the relative abundance of these isotopes. Molar mass, on the other hand, is the mass of one mole (approximately 6.022 x 10^23 atoms) of a substance, typically expressed in grams per mole (g/mol). For the most part, the numerical value of an element’s molar mass in g/mol is numerically equivalent to its atomic weight in amu; however, this only holds true for the element in its most common isotopic form. For elements that have stable isotopes with significant differences in abundance, there can be a clear distinction in the two measurements, meaning they aren't always equal. Thus, stating that they are always equal disregards the isotopic variation that can influence atomic weight. This understanding is crucial in chemistry, particularly in stoichiometry and when working with chemical equations.