CHEMISTRY: THE MATHEMATICS OF FORMULAS AND EQUATIONS(1)

Formulas

represent the composition of a substance.

Chemists

use a specific collective noun to define a particular usable number of particles.

Example problem

What is the formula mass of K₂CO₃

K

2 x 39.1 amu = 78.2 amu

C

1 x 12.0 amu = 12.0 amu

O

3 x 16.0 amu = 48.0 amu

sample problem

What is the percentage of oxygen in K₂CO₃

K

2 x 39.1 amu = 78.2 amu

C

1 x 12.0 amu = 12.0 amu

O

3 x 16.0 amu = 48.0 amu

H

2 atoms x 1 amu/atom = 2 amu

S

1 atom x 32.1 amu/atom = 32.1 amu

O

4 atoms x 16 amu/atom = 64 amu

formula mass

the sum of the atomic masses of all atoms present

percent composition

the composition of a compound as a percentage of each element compared to the total mass of the compound.

percent mass

ratio between the mass of the solute and the total mass of the solution, expressed as a percent

avogadro's number

6.022 x 10^23 - used to define the number of particles in a mole of a substance.

mole (unit)

scientific unit for measuring particles in an substance.