Unit 7: Chemical Quantities

2-Step Conversions

After today, you will be able to…

• Perform two-step conversions using molar mass and representative particles (atoms, molecules, and formula units)

We have already learned…

How to convert moles into particles and vice versa by using the conversion factor…

1 mole = 6.02x10

23 particles

How to convert moles into grams and vice versa by using the conversion factor…

1 mole = atomic mass in grams

These two conversion factors can now be combined…

Particles



Moles



6.02x10

23

Grams

molar mass

Grams



Moles



molar mass

Particles

6.02x10

23

Example:

What is the mass of 1.79x10

24 formula units of K 3 PO 4 ?

K: 1.79x10

24 F.U. K 3 PO 4 U: ? g K 3 PO 4 3 K = 3(39.10) = 1 P = 1(30.97) = 4 O = 4(16.00) = 117.30

30.97

+64.00

212.27

1.79x10

24 F.U. K 3 PO 4 1 x 1 mol K 3 PO 4 6.02x10

23 F.U. K 3 PO 4 .

x 212.27 g K 3 PO 4 1 mol K 3 PO 4

631 g K 3 PO 4

.

=