Honors Chemistry
Name_______________________________ Period___
Introduction to a mole and counting by weight – mole ws #1
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 6.02x1023. 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?
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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?
Find the number of moles – use dimensional analysis, correct sig figs, label (provide the units) and
circle your answer
3. How many moles are in 33 grams of copper?
4. How many moles are in 15 grams of lithium?
5. How many moles are in 31.3 grams of sodium phosphide?
6. How many moles are there in 25.2 grams of magnesium nitrate?
7. If you have 12.0 grams of Lead II sulfite, how many moles of do you have?
8. If you have 1.1 grams of calcium phosphate, how many moles do you have of calcium
phosphate?
9. How many moles are there in 987 grams of ammonium sulfate?
10. How many moles are there in 56 grams of silver cyanide?
Find the number of grams – use dimensional analysis , correct sig. figs, and label and circle your
answer
11. How many grams are in 2.4 moles of sulfur?
12. How many grams are in 88.1 moles of magnesium?
13. How many grams are in 12.3 moles of copper I arsenide?
14. How many grams are in 34 moles of sodium phosphide?
15. How much does 4.2 moles of magnesium nitrate weigh?
16. How many grams are in 25 moles of lead (II) sulfite?