Transcript Topic 1 Molar Mass

Molar Mass (M)
Topic 1.2
Mass
 relative atomic mass (Ar)
 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 (Mr)
 simply comparing a given molecule to carbon
CO2 is 44. C60 is 720, O2 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 CO2 is 44 a.m.u.
 molar mass (M)
 this is how many grams you would have in a mole of
a substance
 therefore CO2 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 (C6H12O6) 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 Na3PO4.
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
• C2H6 → 30.1 g/mol
• Fe(OH)2 → 89.9 g/mol
• C12H22O11 → 342.3 g/mol
• CuSO4 · 5 H2O → 238 g/mol
Converting Moles to Grams and
Grams to Moles
 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
1 mol MgO
= 77.8 g MgO
Mass(g) to moles
• Find the number of moles in 23.5 g of MgO?
23.5 g MgO
1
x
1 mole MgO
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
1 mole MgO_ x _6.02 X 1023 particles MgO
40.3 g MgO
1 mole MgO
= 2.07 X 1023 particles of MgO
here it is again
combining two
conversion factors
1 mole MgO_ x _6.02 X 1023 particles MgO
40.3 g MgO
1 mole MgO
6.02 X 1023 particles MgO
40.3 g MgO molar mass (g)
same thing but be
careful if you do this!
 What is the mass of 2.55 × 1023 atoms of lead?
2.55 × 1023 atoms Pb ×
1 mol Pb
207.2 g Pb
×
23
1 mole Pb
6.02×10 atoms Pb
= 87.8 g Pb
How many atoms in 22 grams of copper?
The Mole Road Map
Mass
“Stuff”
6.022 x 1023
mole
mole
g
Stuff:
g
mole
Mole
mole .
6.022 x 1023
mole .
22.7 L
22.7 L
mole
•Atoms
•Molecules
•Particles
•Electrons
•Ions
•Formula Units
For Gases only:
@ STP
(Standard Temp & Pressure)
(0 oC (273 K) & 1 atm)
Volume