Student Exploration: Moles
Vocabulary: atomic mass, Avogadro constant, conversion factor, dimensional analysis, mole,
molar mass, molecular mass, scienti... [Show More] fic notation, significant figures, unified atomic mass unit
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. In the image to the right, note a dozen eggs, a dozen donuts and
a dozen roses. How many of each item do you have? 12
2. Would a dozen of each object have the same mass? no
3. Suppose you have a dozen carbon atoms, a dozen gold atoms, and a dozen iron atoms.
Even though you have the same number of each, would you expect them all to have the
same mass? Explain.
No, just because they have the same quantity doesn’t mean they weigh the same.
When counting roses, eggs, or donuts, a dozen is a good unit to
use. If you are counting atoms, however, a dozen is not much help.
In the Moles Gizmo, you will learn about a unit used to count atoms.
On the AVOGADRO CONSTANT tab, place the copper (Cu) atom
on the nano-balance on the left, which will show the average atomic
mass of copper rather than the mass of a single copper atom.
1. What is the average mass of a copper atom? 63.546u
The unit “u” refers to unified atomic mass units. A single proton or neutron has a mass of
approximately one atomic mass unit. (Officially, 1 u is one-twelfth the mass of a C-12 atom.)
How many atoms did you need to add? 10232019
Introduction: Since atoms are so tiny, chemists have devised a unit known as the mole. A mole
represents a macroscopic quantity of matter that can be used in the laboratory. One mole of any
element has the same mass in grams as its atomic mass in u.
Question: How many particles are in a mole?
1. Explore: Note the average atomic mass of copper on the nano-balance. Add atoms to the
larger balance until it registers the same number (in g) as the reading on the nano-balance
(in u). Use the Exponent slider to help get the correct amount. Stop adding atoms when the
readings on both balances match exactly (to the nearest 0.001 g).
How many atoms did you need to add? 23
2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum.
A. For each element, how many atoms did you need to add? 15
B. What do you notice about the number of atoms in one mole? 6.63
3. Discover: In each case, you measured out one mole of atoms, since the mass of one mole
of any element, in grams, is equal to its atomic mass, in u. One mole of any element
contains the same number of atoms, a number known as the Avogadro constant.
What is the exact value of the Avogadro constant? 63.252
4. Illustrate: The Avogadro constant is so large it is normally written in scientific notation. To
get an idea of the enormity of the Avogadro constant, write it out in standard form. (You will
need to move the decimal place to the right 23 times, so you will need to add a lot of zeros!)
6.022141793 × 1023
5. Compare: While the number of atoms in a mole is constant, the number of grams in a mole
changes based on the element. The number of grams in a mole (g/mol) is known as its
molar mass, and has the same numerical value as an element’s atomic mass (in u). Use
the Gizmo to find the atomic and molar mass of the following elements. Use proper units [Show Less]