Transcript Chapter 10:The Mole

Chapter 10:The Mole
10-1 Measuring Matter
•Counting Particles…
•The SI Unit for counting is the mole.
•The mole is a number of particles or ‘things’
equal to 6.02 x 1023 of those particles .
•Just like a dozen is 12 a mole is 6.02 x 1023 .
•This number is called Avogadro’s number.
Converting with the mole
• We will use dimensional analysis to convert
with the mole. We always start the same…
• known x unknown units = unknown answer
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known units
• Write the known and unknown for every
problem, then plug them into the equation.
• Try this… How many atoms are in 2.5 moles of
sulfur?
Solve
• Unknown: # of atoms S
• Known: 2.5 moles S
• Plug in… and use 6.02x1023atoms/1mol S
• known x unknown units = unknown answer
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known units
Answer:1.505 x 1024atoms…then round to 2 sd
• 1.5 x 1024atoms of S
Representative Particles
• The representative particle of elements is
the atom.
• The representative particle of ionic
compounds is the formula unit.
• The representative particle of molecular
compounds is the molecule.
• When we count with the mole…this is
what we count, in chemistry.
The Mole and Mass
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Let’s compare the mass of 1 atom of H:He:C
1amu:4amu:12amu
What about 10 atoms of each…
The reduced ratio would be1:4:12
What about 1,000,000 atoms of each….
The reduced ratio would be1:4:12
Is there a number of atoms where the numbers
1:4:12 would be equal to 1g:4g:12g?
….YES…that number is the mole
Mass and the Mole
• The number under each atom now stands
for gram atomic mass.
• If we have a compound, we add up the
masses in the compound and we have
gram molecular mass.
• If it is an ionic compound it will be gram
formula mass.
• A general term is molar mass.
Mass and the Mole
• You can now use the molar mass as a
second conversion factor:
• 1 mol H2O/18.0 g H2O
• How many grams are found in 2.0 moles
of H2O? (Try it.)