Chemical Measurements Objectives: 1. Define the mole and explain its importance. 2. Explain the meaning of Avagadro's number. 3. Explain how molar mass relates the number of particles of a substance to the mass of a substance. 4. Distinguish between molar mass and formula mass. Key Terms: Atomic mass, Formula mass, mole, Avagadro's number, Molar mass

Atomic & Formula Mass Atomic Mass Formula Mass The atomic mass number lists the mass in amu (atomic mass unit) notation. This number is based on the mass of the carbon-12 atom Example: H = 1.01amu, O = 16.00amu, C = 12.01 amu The number is rarely an even whole number due to the fractional abundances of the isotopes Formula Mass Formula mass is determined by adding all of the masses of atoms in a molecule Example: H2O = 18.02amu CO2 = 44.01amu NaHCO3 = 84.01amu Using Masses in Chemical Reactions masses of the reactants need to equal the masses of the molecules and products.

Mole and Avogadro's number the amu has no real experimental significance in the laboratory setting, The mole is was defined by Avogadro A mole is a standard quantity of a substance all moles have the exact number of atoms in 12 grams of carbon-12 A mole of any element is its amu value expressed in the unit gram Each mole contains 6.02 x 1023 pieces This helps scientists convert the atoms and molecules into a useful and predictable units.

Molar mass Molar mass can be used to convert to particles O = 16amu = 16g = 6.02 x 1023 atoms O2 = 32amu = 32g = 6.02 x 1023 molecules = 12.04 x 1023atoms (2 x 6.02 x 1023 atoms) Avagadro's number (6.02 x 1023) established a direct relationship between the mass, quantity, and volume of an item.