Transcript Chemical Measurements - Santa Susana High School

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
– 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.