Topic 1.2

Mass
 relative atomic mass (A r
)
 all masses on the periodic table are compared to CARBON- 12
 no units are necessary since it is just a comparison to carbon- 12
 from this we get the average atomic mass that you would find for an element on the periodic table

 relative molecular mass (M r
)
 simply comparing a given molecule to carbon
 CO
2 is 44. C
60 is 720, O
2 is 16(2) = 32
 atomic or molecular mass
 this is simply the mass of one atom or molecule using a very small unit of measurement called a.m.u.
 therefore CO
2
 molar mass (M) is 44 a.m.u.
 this is how many grams you would have in a mole of a substance
 therefore CO
2 is 44 g/mol

molar mass continued…
• simply change the relative atomic mass from the periodic table for the element/molecule/ compound to grams
• oxygen’s atomic mass is 16.00 amu
•
•
•
 therefore 1 mole of oxygen has a molar mass is 16.00 g/mol
• sugar’s (C
6
H
12
O
6
) atomic mass is 180.0 amu carbon: 12.00(6) = 72.00
hydrogen: 1.00(12) = 12.00
• oxygen: 16.00(6) = 96.00
therefore 1 mole of sugar has a molar mass of 180.00 g/mol

 Calculate the Molar Mass of Na
3
PO
4
.
Atom
Na
P
O
#
3
1
4
Atomic Mass
X 23.0
=
X 31.0
=
X 16.0
=
Total =
Total
69.0
31.0
64.0
164.0
Therefore the molar mass is 164.0 g mol -1

• Give the molar mass (mass of one mole):
• Fe → 55.9 g/mol
•
•
•
•
C
2
H
6
→ 30.1 g/mol
Fe(OH)
2
CuSO
4
→ 89.9 g/mol
C
12
H
22
O
11
→ 342.3 g/mol
· 5 H
2
O → 238 g/mol

 conversion factor will be:
 1 mole molar mass
OR
 molar mass__
1 mole

Number of moles to mass(g)
• Find the mass (in grams) of 1.93 moles of MgO?
1.93 mol MgO
1 x 40.3 g MgO
= 77.8 g MgO
1 mol MgO
Mass(g) to moles
• Find the number of moles in 23.5 g of MgO?
23.5 g MgO x 1 mole MgO
1 40.3 g MgO
= 0.583 mol MgO

Number of grams to moles to particles
• Find the number of particles in 13.9 g of MgO?
13.9 g MgO x 1 mole MgO_ x _6.02 X 10 23 particles MgO
1 40.3 g MgO 1 mole MgO
= 2.07 X 10 23 particles of MgO
1 mole MgO_ x _6.02 X 10 23 particles MgO
40.3 g MgO 1 mole MgO
6.02 X 10 23 particles MgO
40.3 g MgO molar mass (g) here it is again combining two conversion factors same thing but be careful if you do this!

 What is the mass of 2.55 × 10 23 atoms of lead?
2.55
×
10 23 atoms Pb
× 1 mol Pb
6.02×10 23 atoms Pb
×
207.2 g Pb
1 mole Pb
= 87.8 g Pb

How many atoms in 22 grams of copper?

g mole
6.022 x 10 23 mole
mole g
mole .
6.022 x 10 23
Stuff:
•Atoms
•Molecules
•Particles
•Electrons
•Ions
•Formula Units mole .
22.7 L
22.7 L mole
For Gases only:
@ STP
(Standard Temp & Pressure)
(0 o C (273 K) & 1 atm)