Chemical Formulas _ Formula Mass

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Chemical Formulas _ Formula Mass Powered By Docstoc
					Chemical Formulas:

  Formula Mass
       &
   Molar Mass
    Subscripts in Chemical Formulas
n   Subscripts show # atoms each element in
    representative unit
n   Subscripts after parentheses refer to
    everything inside ( )
             Molar mass of an element
n   Molar mass = mass (in grams) of 1 mole of
    any pure substance

n   Molar mass of element is:
    n   numerically equal to atomic mass, but
         n   units change from amu to grams per mole (g/mol)
          Molar mass of elements
n   Na has atomic mass of 22.98977 amu
    n   molar mass = 22.98977 grams/mol

n   K has atomic mass of 39.0983 amu
    n   molar mass = 39.0983 grams/mol

n   Ca has atomic mass of 40.08 amu so
    n   molar mass = 40.08 grams/mol
Round masses to whole number

Na = 22.98977 grams
    round to 23 grams

K = 39.0983 grams
    round to 39 grams

  Ca = 40.08 grams
     round to 40 grams
                  Molar mass

n   Also called
     formula mass     or


            gram formula mass
      Mole to mass conversions

n   Use PT for conversions involving mass

Unless you want to memorize the masses of
 all the elements!!
       Molar Mass of Compounds
n = to sum of masses of atoms in compound's
  formula
n Round atomic masses to whole number

Ex: H2O
   n 2 H’s = 2 x 1g = 2g

   n 1 O = 1 x 16g = 16g



n   Molar mass H2O is sum: 2g + 16g = 18g
   Molar Mass of Compounds

Try CH4
n 1 C = 1 x 12g = 12g

n 4 H’s = 4 x 1g = 4g



n Sum   = 4g + 12g = 16g

				
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