Mole
The mol is the SI unit for amount of a substance. The mol allows
chemists to count particles by massing them.
1 mol of any substance contains the same number of particles as
there are in exactly 12 g of carbon-12. The number of particles
in 12 g of carbon-12 is 6.022 x 1023, this is known as Avogadro’s
number.
1 mol of Cu = 6.022 x 1023 atoms
1 mol of H2O = 6.022 x 1023 molecules
1 mole of CaCl2 = 6.022 x 1023 formula units
1 mol of marbles stacked tightly together would cover the USA 70
miles deep!
Molar mass
Molar mass is the mass in grams per mol of a substance. Molar
mass is determined by totaling of the average atomic masses of
each element in its chemical formula.
For example, the molar mass of sodium is 22.99 grams/mol, the
molar mass of H2 equals 2.016 grams/mol (1.008 + 1.008), and
the molar mass of water is 18.02 grams/mol (16.00 + 2.016, note
the use of significant figures)
Determine the molar mass of nitrogen (III) oxide
N2O3
2(14.01)
+ 3(16.00)
76.02 g/mol
1
Determine the molar mass of copper (II) sulfate pentahydrate
CuSO4 . 5H2O
63.55
32.06
64.00
+ 5(18.02)
249.71 g/mol
2
Molar mass can be used as a conversion factor
For example, the number of moles of water in 25.0 grams can be
determined as follows.
25.0 g H2O x 1 mol H2O = 1.39 mol H2O
18.02 g
How many grams are present in .074 mol of carbon dioxide?
.074 mol CO2 x 44.01 g CO2 = 3.3 g CO2
1 mol CO2
Avogadro’s Number can be used as a conversion factor to go
between atoms, formula units or molecules and moles
How many molecules of water are present in .0416 mol of water?
.0416 mol H2O x
6.022 x10 23 molecules H 2 O
= 2.51 x 1022 molecules H2O
1 mol H 2 O
How many atoms are present in 2.96 g of silver?
6.022 x10 23 atoms Ag
1 mol Ag
2.96 g Ag x x
= 1.65 x1022 atoms Ag
x
107.87 g Ag
1 mol Ag
3