Transcript Chapter 10 - The Mole

Chapter 10 - The Mole &
Avogadro’s Number
Measuring Matter
Sections 10.1  10.3
Measuring Matter/Counting Units
• One pair = 2
(boots, shoes)
• One dozen = 12
(eggs, donuts, roses)
• One gross = 144
(pencils)
• One ream = 500
(sheets of paper)
Measuring a Mole – units
used to count particles
• Atoms are so tiny chemists count them using a
unit of measurement called a “mole”
• 1 mole = 6.02 x 1023 (Avogadro’s Number)
atoms/particles/ions/formula units/molecules
• This is a very large number because it
measures extremely tiny items
• 602,000,000,000,000,000,000,000
How Big is a Mole?
• One mole of pennies would allow every person on
Earth to spend a million dollars an hour, day and night,
and still have half of it unspent when they died
• One mole of popcorn would cover every dry
surface of the Earth to a depth of six miles
One mole of stacked pennies would reach to the moon
and back 16 times
• One mole of marshmallows
would cover the United States
to a depth of 650 miles
History of Avogadro’s Number
Avogadro: 1811 – equal volumes of gases at the
same temperature and pressure contain equal
numbers of molecules
Cannizzaro: 1861 – developed atomic weights for
known elements
Loschmidt: 1865 – determined the number of atoms
present in a given volume of air
Ostwald: 1902 – developed the concept of the mole
1971 – the true value, 6.02x1023, was actually
determined and is called Avogadro’s number since
the entire string of events started with his findings in
1811
The Law of Conservation of Mass
• According to the Law of Conservation of Mass,
Mass of reactants = mass of products
Mass of starting substances = mass of ending
substances
• So the production of one water molecule requires 2
hydrogen atoms and 1 oxygen atom.
Therefore:
two atoms of hydrogen + one atom of oxygen  1 water molecule
And
12.04x1023 hydrogen atoms + 6.02x1023 oxygen atoms 
6.02x1023 water molecules
The Law of Definite Proportions and Ratios
of Atoms
Law of Definite Proportions – atoms combine in small whole
number ratios to form compounds
Example: Water- two atoms of Hydrogen will always combine
with one atom of Oxygen to form one molecule of water
Relationships between moles,
atoms and the gram mole
The atomic mass ratio of hydrogen to oxygen is 1 amu : 16 amu
The gram mole ratio between hydrogen and oxygen is 1 g : 16 g
So, chemists can determine how many atoms are present in a sample.
One gram of hydrogen would contain exactly 6.02x1023 atoms, or Avogadro’s Number
of atoms. Two grams of hydrogen atoms would contain 12.04x1023 hydrogen atoms.
Also, 16 gram moles of oxygen would contain 6.02x1023 atoms.
= 6.02x1023 atoms
= 1 mole
2 grams of hydrogen
= 12.04x1023 atoms
= 2 moles
16 grams of oxygen
= 6.02x1023 atoms
= 1 mole
32 grams of oxygen
= 12.04x1023 atoms
= 2 moles
Therefore: 1 gram of hydrogen
In Conclusion:
• 2 atoms of hydrogen + 1 atom of oxygen
= 1 water molecule
• 2 amu of hydrogen
+ 16 amu’s of oxygen = 18 amu’s of water molecules
• 2 g of hydrogen
+ 16 grams of oxygen = 18 grams of water molecules
• 12.04x1023 atoms H + 6.02x1023 atoms O
= 6.02x1023 atoms H2O
molecules
• 2 moles of H atoms + 1 mole of O atoms
= 1 mole of water molecules
Moles
Particles
Conversion
x 6.02 x 1023
Moles
Particles
Atoms, molecules,
ions, formula units
÷ 6.02 x 1023
EXAMPLE PROBLEMS:
1) Convert 3.5 moles to atoms
2) Convert 18.06 x 1023 atoms to moles
Convert from moles to particles
3) 2.7 moles of lithium
4) 1.8 moles of sodium chloride
5) 5.3 moles of bromine
6) 4.7 moles of potassium oxide
Convert from particles to moles
7) 4.32 x 1024 atoms of calcium
8) 2.7 x 1020 atoms of copper
9) 2.5 x 1024 molecules of sodium chloride
10) 5.32 x 1023 molecules of calcium chloride
You try these…
11) 25 moles to particles
12) 4.08 x 104 particles to moles
13) 0.002 moles to particles
14) 2.3 x 1016 particles
Homework
Complete on another sheet of
paper showing your work!
Moles to particles
1) 2.7 moles
2) 1.8 moles
3) 5.3 moles
4) 4.7 moles
Particles to moles
24
10
5) 4.32 X
6) 2.70 X 1020
24
7) 2.50 X 10
8) 5.32 X 1023