Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. In the image to the right, note a dozen eggs, a dozen donuts and
12
a dozen roses. How many of each item do you have?
no
2. Would a dozen of each object have the same mass?
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 I would not expect them to have the same mass because they are made different atoms.
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? 63.546 u
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.
20
How many atoms did you need to add? 1.01 x 10
2019
, Get the Gizmo ready:
Activity A:
Select the AVOGADRO CONSTANT tab.
Molar Mass Turn on Show hints and 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).
19
How many atoms did you need to add? 1.395 x 10
2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum.
19 19
carbon- 7 x 10 aluminum-2 x 10
A. For each element, how many atoms did you need to add? sulfur- 1 x 1019
carbon-12.011u aluminum-26.982u
B. What do you notice about the number of atoms in one mole? sulfur-32.065u
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.
23
What is the exact value of the Avogadro constant? 6.02 x 10
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!)
602,000,000,000,000,000,000,000
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.
S: Atomic mass 32.06 Molar mass 32.065u
Al: Atomic mass 26.982 Molar mass 26.982u
(Activity A continued on next page)
2019
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