Chemical Formulas: Formula Mass

1
Chemical Formulas Formula Mass Molar
Mass
2
Subscripts in Chemical Formulas

• Subscripts show atoms of each element
• in representative unit
• Subscripts after parentheses refer to everything
  inside ( )

3
Molar mass of an element

• molar mass is mass (in grams) of 1 mole of any
  pure substance
• molar mass of element is
• numerically equal to atomic mass, but
• units change from amu to grams per mole (g/mol)

4
Molar mass of elements

• Na has atomic mass of 22.98977 amu
• molar mass 22.98977 grams/mol
• K has atomic mass of 39.0983 amu
• molar mass 39.0983 grams/mol
• Ca has atomic mass of 40.08 amu so
• molar mass 40.08 grams/mol

5
Round masses to whole number Na 22.98977
grams rounds to 23g K 39.0983 grams
rounds to 39g Ca 40.08 grams rounds to 40g
6
Molar Mass

• always refers to mass in grams per mole (g/mol)
• formula mass (FM) or gram formula mass (GFM)
  refers to mass in grams (g)

7
Mole to Mass conversions

• Use PT for conversions involving mass
• Unless you want to memorize the masses of all the
  elements!!

8
Molar Mass of Compounds

• to sum of masses of all atoms in compound's
  formula
• round atomic masses to whole number
• ex H2O
• 2 Hs 2 x 1g 2g
• 1 O 1 x 16g 16g
• FM of H2O is sum 2g 16g 18g
• molar mass of H2O is 18g/mol

9
Molar Mass of Compounds

• CH4
• 1 C 1 x 12g 12g
• 4 Hs 4 x 1g 4g
• FM is sum 4g 12g 16g
• Molar mass is 16g/mol

10

• Challenge find FM of
• CuSO45H2O
• 4Ba3(PO4)2