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?
A dozen represented as 12 in total is 36
2. Would a dozen of each object have the same mass?
No, it will not have the same mass or weight.
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.
By weight they have the same mass. mass is the measure of the amount of
matter or the substance that makes up an object. But the number of the
atom is different.
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?
63.54u
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
Activity A: ready:
Molar Mass ● Select the AVOGADRO CONSTANT tab.
● 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).
How many atoms did you need to add?
6.02214076 x 10^23
2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum.
A. For each element, how many atoms 6.02214076 x 10^23
did you need to add?
Carbon, sulfur and aluminum all
B. What do you notice about the number need the same amount of atoms
of atoms in one mole? it's also the same amount as the
Avogadro constant
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?
6.02214076 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!)
602,214,179,300,000,000,000,000
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