Chemical Formulas: Formula Mass & Molar Mass

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

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)

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

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

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)

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

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

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

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