The Mole. 6.02 X 10 23. The Mole. 1 pair = 2 representative particles 1 dozen = 12 representative particles 1 mole = 6.02 x 10 23 representative particles The Mole (mol): A unit to count numbers of particles 1 dozen cookies = 12 cookies 1 mole of cookies = 6.02 X 10 23 cookies
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6.02 X 1023
Note that the NUMBER is always the same, but the MASS is very different!
Refers to the species present.
Usually atoms, molecules, or formula units.
Atomic Nitrogen = N
Nitrogen gas = N2
Water = H2O
Calcium ion = Ca2+
Glucose = C6H12O6
1 mole of all of these =
6.02 x 1023 rep. particles
6.02 x 1023 particles
6.02 x 1023 particles
Note that a particle could be an atom OR a molecule!
1. Number of atoms in 0.500 mole of Al
a) 0.500 mole of Al
b) 6.02 x 1023 Al atoms in 1 mole
c) So, in 0.5 mole, 3.01 x 1023 Alatoms
2.Number of moles of S in 1.8 x 1024 S atoms
a) 6.02 x 1023 S atoms in 1.0 mole of S atom
b) So, 3 x 6.02 x 1023 = 1.8 x 1024 S atoms
in 3 x 1 mole= 3.0 mole S atoms
c) 3.0 mole S atoms
Gram Atomic Mass –
Atomic mass of an element expressed in grams.
The gram atomic mass is the mass of 1 mol of atoms of any element.
1 mole of C atoms = 12.0 g
1 mole of Mg atoms = 24.3 g
1 mole of Cu atoms = 63.5 g
# of C atoms in12.0 g of C atoms = # of Mg atoms in24.3 g of Mg atoms = # of O atoms in 16.0 g
How many is that?
6.02 x 1023!!
Gram Molecular Mass/Molecular Weight
Gram Formula Mass/Formula Weight
What is the gram atomic mass (GAM) of 1 mol of the following compounds?
Gram Molecular Mass of SO3 and H2O = ?
SO3 = 80.1g H2O = 18 g
Gram Formula Mass of NaCl and CaI2 = ?
NaCl = 58.5 g CaI2 = 293.9 g
= 79.9 g/mole
= 118.7 g/moleMolar Mass( atoms, molecules and compounds)
Molar Mass: mass of one mol of any substance(usually we round to the tenths place).
Mass in grams of 1 mole equal numerically to the sum of the atomic masses
1 mole of CaCl2 = 111.1 g/mol
1 mole Ca x 40.1 g/mol
+ 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2
1 mole of N2O4 = 92.0 g/mol
B.MolarMass of antacid Al(OH)3 = ? Grams/mole
2. How many moles are in 92.2 g iron (III) oxide?
2 x 30.97
+ 8 x 16.00
What is the formula mass of Ca3(PO4)2 ?
1 formula unit of Ca3(PO4)2
Standard temperature and pressure:
0°C and 101.3 kPa or 1 atm
At these conditions, 1 mol of any gas = 22.4 L
1. What is the volume, in L, at 0.60 mol SO2 gas at STP?
13.44 L SO2 (g)
2. The density of a gaseous compound containing carbon and oxygen is 1.964 g/L at STP. What is the molar mass?
3. A gaseous compound composed of sulfur and oxygen is linked in the formation of acid rain and has a density of 3.58 g/L at STP. What is the molar mass?
4. What is the density of Kr gas at STP?
NA=6.02 x 1023
Gram atomic mass/
Gram molecular mass/
Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?
3.00 moles Al ? g Al
1.Molar mass of Al 1 mole Al = 27.0 g Al
2. Conversion factors for Al
27.0g Al or 1 mol Al
1 mol Al 27.0 g Al
3. Setup3.00 moles Al x 27.0 g Al
1 mole Al
Answer = 81.0 g Al
molar mass Avogadro’s numberGrams Moles particles
Everything must go through Moles!!!
How many atoms of Cu are present in 35.4 g of Cu?
35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu
= 3.4 X 1023 atoms Cu
How many atoms of K are present in 78.4 g of K?
How many atoms of O are present in 78.1 g of oxygen?
78.1 g O2 1 mol O2 6.02 X 1023moleculesO2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2
The percent by mass of each element in a compound.
% mass of element = grams of element grams of compound
1. Calculate the percent composition of each element in propane, C3H8.
C = 81.82%
H = 18.18%
The formula of a compound that expresses the smallest whole number ratio of the atoms present.
Ionic formula are always empirical formula
The formula that states the actual number of each kind of atom found in one molecule of the compound.
The lowest whole number ratio of atoms of the elements in a compound.
Example: CO (could be C2O2, C4O4, but not CO2)
*Empirical Formula may or may not be the molecular formula.
Hydrogen Peroxide = H2O2 but the empirical formula is HO
Carbon dioxide = CO2 and it is the empirical formula
1. Determine the mass in grams of each element present, if necessary.
2. Calculate the number of moles of each element.
3. Divide each by the smallest number of moles to obtain the simplest whole number ratio.
*Be careful! Do not round off numbers prematurely
1. What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen?
Looks hard, but follow the three steps…
Convert % to moles.
1.85 mol N
4.63 mol O
Divide both answers by the lowest one.
1.85 mol N is lowest.
1 mol N
2.5 mol O
If one answer is a decimal, multiply both by a number so it is converted to a whole number.
2.5 mol O becomes 5 mol
1 mol N becomes 2 mol
NO2 2 atoms of O for every 1 atom of N
1 mole of NO2 : 2 moles of O atoms to every 1 mole of N atoms
A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance.
require mole ratios so convert grams to moles
moles of N = 2.34g of N = 0.167 moles of N
moles of O = 5.34 g = 0.334 moles of O
Either the same as the empirical formula or a simple whole number multiple of it.
Known molar mass of molecule =
Molar mass of empirical form.
the number of
units needed (EFU).
Multiply empirical formula with EFU to get the molecular formula
A compound has an empirical formula of NO2. The colourless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?