# Chemical Formulas _ Formula Mass by pptfiles

VIEWS: 4 PAGES: 9

• pg 1
```									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

```
To top