Directions: Follow the instructions to go through the simulation. Respond to the questions and
prompts in the orange boxes.
Vocabulary: atomic mass, Avogadro constant, conversion factor, dimensional analysis, mole, molar mass,
molecular mass, scientific notation, significant figures, unified ato...
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?
They would have different masses because they are all different objects.
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.
I would not expect all atoms to have the same mass because atoms can be made from
several different isotopes which all weigh different amounts.
Gizmo Warm-up
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.)
2. To gain an idea as to how many atoms are in a gram or so of copper, use the larger balance on the right.
Press Add atoms to put a scoop of atoms in the weighing dish, and keep adding until the balance registers
between 1 and 2 grams. If you don’t seem to be making much progress, adjust the exponent using the
slider, which will make the scoop size bigger. How many atoms did you need to add?
Get the Gizmo ready:
Activity A:
● Select the AVOGADRO CONSTANT tab.
Molar Mass ● Turn on S how hints a
nd check that Copper (Cu)
is selected.
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?
1 x 10^19
2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum.
A. For each element, how many atoms did you Carbon : 3 x 10^19
need to add? Sulfur : 1 x 10^19
B. What do you notice about the number of
atoms in one mole?
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?
6.02 x 10^23
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!)
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