The Mole

-  Chemists work in the macroscopic world of grams and liters

-  But chemists are also interested in the microscopic world of atoms and molecules which are VERY, VERY small

-  The mole is the bridge from the microscopic world to the macroscopic world

24 cans / = 1 case
2 shoes, earrings, mittens / = 1 pair
12 donuts, roses, eggs / = 1 dozen
6.02 X 1023 molecules, atoms, ANYTHING / = 1 mole

A mole is the amount of any substance.

1 mole Na = 6.02 X 1023 atoms of Na

1 mole Cl = 6.02 X 1023 atoms of Cl

1 mole NaCl = 6.02 X 1023 molecules of NaCl

1 mole of donuts = 6.02 X 1023 donuts

E.g. The average galaxy has 150 billion stars. It is estimated that there are 125 billion galaxies in the universe. How many moles of stars in the universe?

E.g. It is estimated that there are 200 million insects per person. There are approximately 7 billion people in the world. How many moles of insects are there in the world?

Homework: p. 168 #1-6


Molar Mass

Why 6.02 X 1023?

Couldn’t Avogadro have picked an easier number to work with??

-  It has been determined experimentally that there are 6.02 X 1023 carbon atoms in 12 g of C-12.

-  Recall: 1 atom of C-12 has a mass of 12 u

-  1 mole of C-12 (6.02 X 1023 atoms) has a mass of 12 g

-  The mole allows us to easily convert from atomic mass (microscopic) into grams (macroscopic)

1 C-12 atom has a mass of 12 u

1 mole of C-12 has a mass of 12 g

OR 12 g/mole

1 O-16 atom has a mass of 16 u

1 mole of O-16 has a mass of 16 g

OR 16 g/mole

This applies to molecules as well:

-  The mass of one molecule of H2O = 2 X 1.01 u + 16.00 u = 18.02 u

-  The mass of one mole of H2O = 18.02 g

The mass of 1 mole of any substance is called its molar mass and it is written in units of g/mol

E.g. The molar mass of potassium is 39.10 g/mol (i.e 6.02X 1023 atoms of K have a mass of 39.10 g)

E.g. * Don’t forget about diatomic molecules!!

The molar mass of oxygen atoms (O) is 16.00 g/mol. The molar mass of oxygen molecules (O2) is 32.00 g/mol (16.00 X 2)

E.g. What is the molar mass of ammonium phosphate?

M(NH4)3PO4 = 3(N + 4H) + P + 4O

= 3N + 12H + P + 4O

= 3(14.01) + 12(1.01) + 30.97 + 4(16.00)

= 149.12 g/mol

Homework:

P. 170 #7-13; p. 171 #1-5