What term describes the mass in grams of one mole of a substance?

• A. molar mass
• B. mole
• C. Avogadro's number
• D. average atomic mass

Answer: (A)

Mass in grams of one mole of a substance is molar mass, because it expresses how heavy one mole of that substance is and is given in grams per mole. For elements, the molar mass equals the atomic mass value on the periodic table, in g/mol. For compounds, add together the molar masses of all the atoms in the formula according to how many of each atom appear. For example, one mole of carbon weighs 12.00 g, so its molar mass is 12.00 g/mol. Water has a molar mass of about 18.015 g/mol (2 H + 1 O). The other terms don’t describe mass per mole: a mole is the amount of substance, Avogadro’s number is the number of particles per mole, and average atomic mass is the weighted average of isotopic masses (in amu), not the grams-per-mole mass.