Atomic Masses & the MOLE…. Counting Atoms. Masses of atoms expressed in grams are extremely small. An atom of O-16 literally weighs 0.0000000000000000000000266 g For most calcs in chemistry it is easier to use a relative atomic mass.
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Atomic Masses & the MOLE…
Here’s how the masses were calculated on the Periodic Table:
Calculating average atomic masses:
Naturally occurring copper consists of 69.17% Cu-63, which has a mass of 62.9296011 amu, and 30.83% Cu-65, with a mass of 64.9277937 amu.
+ (0.3083)(64.9277937 amu)
1 mole is always = 6.02 x 1023 items
How many moles of Magnesium
is 1.25 x 1023 atoms of Magnesium?
Using the mole in calculations #1
1 mol Mg = 6.02 x 1023 atoms Mg
The desired conversion is: atoms moles
1 mole Mg
1.25x1023 atoms Mg
= .208 mol Mg
How many atoms of Gold do we have if we have .0327 moles of Gold?
Using the mole in calculations #2
1 mol Au = 6.02 x 1023 atoms Au
The desired conversion is: moles atoms
.0327 mole Au
1 mole Au
= 2.23x1022 atoms Au
How many atoms of Carbon are in 2.12 mols of Propane (C3H8)?
Using the mole in calculations #3
1 mol C3H8 = 6.02x1023 molecules C3H8
1 molecule C3H8 = 3 atoms C
moles molecules atoms
6.02x1023 molecules C3H8
3 atoms C
1 molecule C3H8
1 mole C3H8
=3.83x1024 atoms C
18.99g F atoms=1 mol F atoms=6.02x10 F atoms
Ca: (1)(40.09 g/mol) =
O: (2)(15.99 g/mol) =
H: (2)(1.008 g/mol) =
What is the MM of glucose (C6H12O6)?
(12H’S)(1.008 g/mol) =
(6O’S)(15.99 g/mol) =
1 mole of C6H12O6 or
6.02x1023 molecules of the compound –weighs 180.1 grams
How many grams are in 9.45 mol of Dinitrogen Trioxide (N2O3)
Using the molar mass in calculations:
The only connection to N2O3 and its mass is how much 1 mol of the compound weighs. But, using it as a comparison we can calculate the mass of 9.45 mol.
Step 1: Determine the mass of 1 mol of N2O3
If 1 mole of N2O3 weighs 75.99g than how much will 9.45 mols of N2O3 weigh?
Step 2: Convert the given moles to grams using the Molar mass equality.
75.99 g N2O3
9.45 mol N2O3
1 mol N2O3
=718 g N2O3
Find the number of moles of
92.2g of Iron (III) Oxide (Fe2O3)
The only connection to the mass of Fe2O3 and how that corresponds to mols is how that 1 mol of the compound weighs a certain # of grams. Using that we can figure out how many moles weigh 92.2 g
Step 1: Determine the mass of 1 mol of Fe2O3
If 1 mole of Fe2O3 weighs 157.67g than how many mols will weigh 92.2 g of Fe2O3?
Step 2: Convert the given mass to mols using the Molar mass equality
1 mol Fe2O3
92.2 g Fe2O3
159.67 g Fe2O3
Molar Volume of a Gas
1 mole of any gas under the specific conditions of 0°C and 1 atm (STP) will occupy a volume of 22.4 L.
molecules of CO2
molecules of O2
What volume, in Liters, does 0.60 mol of SO2 gas occupy at STP?
The only connection to the volume of any gas and how that corresponds to mols is that 1 mol of a gas occupies 22.4 Liters of space. Using that we can figure out the volume of 0.60 mols of a gas at STP.
Step 1: Use the equality 1 mol = 22.4 L to do the conversion
22.4 L SO2
0.60 moles SO2
1 mole SO2
= 13 L SO2
Aspartame is an artificial sweetener that is 160 times sweeter than sugar when dissolved in water. It is marketed as Nutra-Sweet (C14H18N2O5).