Honors Chemistry
Name_______________________________ Period___
Introduction to a mole and counting by weight – mole ws #1 and prelab
A mole is:
a) A mammal known for digging up gardens.
b) A small, dark spot on the skin.
c) A spy embedded within an enemy government.
d) 6.02 × 1023 particles of a substance.
e) All of the above.
The correct answer, of course, is “e”. In chemistry, the mole (mol) is defined as an amount of a substance that
contains 6.02 × 1023 particles of that substance. This number, called Avogadro’s number, is special because
this number of particles has a mass in grams that is equal to the mass in universal mass units of a single
particle of the substance.
Question: What Is a Mole and Why Are Moles Used?
Answer: A mole is simply a unit of measurement. Units are invented when existing units are inadequate.
Chemical reactions often take place at levels where using grams wouldn't make sense, yet using absolute
numbers of atoms/molecules/ions would be confusing, too. Mole is 6.02x1023 of ANYTHING you can count - it
is a counting number like a dozen.
Further Explanation for those not happy with the above answer: Like all units, a mole has to be based on
something reproducible. A mole is the quantity of anything that has the same number of particles found in
12.000 grams of carbon-12. That number of particles is Avogadro's Number, which is roughly 6.02x10 23. A
mole of carbon atoms is 6.02x1023 carbon atoms. A mole of chemistry teachers is 6.02x1023 chemistry
teachers. It's a lot easier to write the word 'mole' than to write '6.02x1023' anytime you want to refer to a large
number of things! Basically, that's why this particular unit was invented as one of the SI units.
The Atomic Mass Unit is defined as 1/12 of a Carbon-12 atom. It is the standard in the AMU scale. The mass of
all atoms in AMUs is defined relative to this standard. Likewise, the mass of a mole is defined as the number in
grams that is equal to the average AMU of the element. For example the average atomic mass of Carbon is
12.011 AMU. The mass of one mole of Carbon is equal to 12.011 grams. The mass of one mole of Lead is equal
to 207.2 grams. The mass of one mole of a molecule is equal to the mass of one mole of each of the atoms in
the compound. For example the mass of one mole of Silicon dioxide is equal to 28.0855 grams for the Silicon
plus 15.9994 grams for each of the oxygens.
The mass of one mole of substance (element or compound) is called the substance’s molar mass in units of
grams/mole.
Why don't we simply stick with units like grams and kilograms? Moles give us a consistent method to convert
between atoms/molecules/formula units and grams. It's simply a convenient unit to use when performing
calculations. Okay... you may not find it too convenient when you are first learning how to use it, but once you
become familiar with it, a mole will be as normal a unit as, say, a dozen or a byte.
If you missed today’s class watch this video: http://www.gpb.org/chemistry-physics/chemistry/701
1. Guess how many pieces of candy are in the box of movie theater candy? ___________________
2. Think about it, how can we figure out how many pieces of candy are in the box?
1. Define Mole:
2. How are the terms molar mass and atomic mass different from each other?
Question: How do scientists find the molar mass of a substance?
1. Calculate: The molar mass of a molecule is the sum of the masses of each atom in the molecule.
 Iron’s atomic mass is 55.85 g/mole, carbon’s mass is 12.01 g/mole, and oxygen’s mass is 16.00 g/mole
 Where did these masses come from? Look at the periodic table!.
 Calculate the molecular mass of water by adding the atomic masses of two hydrogen’s and one
oxygen:
2. Infer: A mole of a substance has a mass in grams that is equal to the molar mass that we determine from
looking at the periodic table. For example, a carbon atom has a mass of 12.01 g/mole.
3. Percent Composition :
Practice: Calculate the percent composition of hydrogen and oxygen in water:
Sample lab calculations:
Iron III Chloride
1. Mass of empty container
4. Formula:
2. Mass the sample. (with container)
_____________
3. Mass of sample (without the container)
5. Molar mass
6. Percent of Iron in Iron III chloride:
______________
Show work here
7. Percent of chlorine in Iron III chloride:
8.. # of moles in your sample
9 . # of FU in your sample (start with the moles of your sample)
25. # of atoms in your sample (start with FU)
26. # chlorine atoms in your sample (start with formula units)
27. # chlorine atoms in your sample (start with your mass)