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 = grams/mol
K has atomic mass of amu
molar mass = grams/mol
Ca has atomic mass of amu so
molar mass = grams/mol

5. Round masses to whole number
Na = grams
rounds to 23g
K = grams
rounds to 39g
Ca = 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 H’s = 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 H’s = 4 x 1g = 4g
FM is sum = 4g + 12g = 16g
Molar mass is 16g/mol

10. Challenge: find FM of
CuSO4•5H2O
4Ba3(PO4)2