Topic: Formula Mass

Write the chemical formula based on the structural formula

below

C2H6O2

Formula mass of an element

formula mass of element = to atomic mass – But units change from amu to grams

Formula mass of elements (p.1 in packet)

Zinc: – atomic mass of 65.409 amu so formula mass = 65grams

Nitrogen:– atomic mass of 14.0067 amu so formula mass = 14 grams

Neon:– atomic mass of 20.190 amu so formula mass = 20 grams

Formula Mass of Compounds

= sum of masses of atoms in formula

Round atomic masses to whole number

Step 1 count atoms

Step 2 look up mass

Step 3 multiply

Step 3 add

Ex: H2O

H = 2

O = 1

x 1

x 16

= 2= 16

18 g

Formula Mass of Compounds

Try CH4

C = 1 X 12 = 12

H = 4 X 1 = 4Sum = 16 g

Formula Mass for Al(NO3)3

Al(NO3)3

Al = 1

N = 1 X 3 = 3

O = 3 X 3 = 9

• Al = 1 x 27 = 27

• N = 3 x 14 = 42

• O = 9 x 16 = 144

213 g