1. Defining the Mole & Mole Practice Problems
Kelsey Flynn
B Block
May 2010

2. The Mole Using a unit called mole ( also written as mol)
Particles such as atoms, molecules and ions, can be counted three ways by the:
the mole gives the number of particles
mass of particles, or
the volume of the gas particles

3. Avogadro’s Number 23
6.02 x 10
Particles
One mole =
A mole of a substance, an element or a compound, contains the same number of particles, 6.02 x 1023.

4. Practice Questions!
1. How many moles are in 6.5 x 1021 molecules of CO
Answer: 6.5 x 1021 molecules of CO x 1 mol of CO = mol CO
6.02 x 1023 molecules of CO
2. How many molecules of H2O is needed to make 0.95 mole of it.
Answer: 0.95 mole of H2O x 6.02 x 1023 molecules H2O = 5.72 x molecules H2O
1 mole H2O
3. How many atoms are present in 2.25 mole of Fluorine.
Answer: 2.25 mole of Fluorine x 6.02 x 1023 atoms F = 1.35 x 1024 atoms F
1 mole F

5. Molar Mass
The atomic mass of an atom is found on a periodic table, it is measured in a.m.u. The molar mass of an element, is measured in grams, is the same as the atomic mass.
Ex: Oxygen
atomic mass =16 a.m.u
molar mass = 16 g

6. Molar Mass
The molar mass of a compound is the sum of the masses of all the elements in the compound.
A mole is measured in grams.
Ex: Nitrous Acid, HNO2
Molecular mass Molar Mass
H= 1 a.m.u H= 1 g
N= 14 a.m.u N= 14 g
O2= 32 a.m.u O2= 32 g
47 a.m.u g
molecular mass of molar mass of HNO2 is 47 g
HNO2 is 47 a.m.u

7. Practice Questions!
How many grams of each element do you need to get one mol?
1. Xenon
Answer: g
2. Silver
Answer: g
3. Tin
Answer: g

8. Molar Volume
The volume of gases can be measured at SATP, standard ambient temperature and pressure.
At SATP, one mole of a gas occupies a volume of 24.8 L. That is the molar volume.
The unit for molar volume is L/mol.

9. Molar Volume One mol of gas = 24.8 L at SATP SATP = 25º C = 298.15K or
100 kPa

10. Practice Questions! 1. Find the volume of 0.5 moles of CO2 at SATP.
Answer: 0.5 moles of CO2 x L of CO2 = 12.4 L CO2
1 mole CO2
2. How many moles are there in 4.75 L of a gas at SATP?
Answer: 4.75 L of a gas x 1 mole of a gas = 0.2 mole of a gas
24.8 L of a gas
3. What is the density (g/L) of NH4 at SATP?
Answer: NH4 density (g/L) = 18 g NH4 = 0.73 NH4 g/L
24.8 L NH4