In the last section, you learned that

• for any element, a mole is the atomic mass expressed in grams, and
• for any compound, a mole is the formula or molecular mass in grams.

Atomic mass, formula mass, and molecular mass are usually expressed in atomic mass units, abbreviated amu. When the mass of an element or compound is expressed in grams, this is called molar mass. Molar mass is the mass of one mole of a substance, and the units are grams/mole. Remember, you can get the mass of the elements from the periodic table.

Let’s practice a few problems together. Use the periodic table from the STAAR reference material to help you during this exercise.

Problem 1

What is the molar mass of one mole of copper (II) nitrate, Cu(NO₃)₂?

Problem 2

A laboratory exercise calls for two moles of sodium chloride, NaCl. How many grams do you need?