(Page 221-222)

Formula Mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula. It is reported as amu (atomic mass units.

Example:

Average atomic mass of H: 1.01 amu

Average atomic mass of O: 16.00 amu

2 H atom x 1.01amu/H atom = 2.02 amu

1 O atom x 16.00 amu/O atom = 16.00 amu

H₂0 has a formula mass of 18.02 amu

Molar Mass is numerically equal to its formula mass. Therefore, the molar mass of water is 18.02 g/mol

Find the formula mass and molar mass of:

H2SO₄

Ca(NO₃)₂

PO₄^-

MgCl₂

Percentage Composition (page 226)

Find the % O in H₂O.

1 O atom = 16.00 g/mol

2 H atoms= 2.02 g/mol

mass of H₂O = 18.02 g/mol

% O = 16.00 g/mol X 100 = 88.79% O in H₂O

18.02 g/mol

Calculation of an empirical formula (page 231)

From Lab Data:

From & composition: