2019

Name: Date:

Student Exploration: Moles

Vocabulary: atomic mass, Avogadro constant, conversion factor, dimensional analysis, mole,

molar mass, molecular mass, scientific 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?

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.

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?

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?

Bailey Sage 10-13-19

12

no

No I would not expect them to have the same mass because they are made different atoms.

63.546 u

1.01 x 10 20

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2019

Activity A:

Molar Mass

Get the Gizmo ready:

 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?

2. Explore: Repeat the same procedure with carbon, then sulfur and aluminum.

A. For each element, how many atoms did you need to add?

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?

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!)

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 Molar mass

Al: Atomic mass Molar mass

(Activity A continued on next page)

1.395 x 1019

carbon- 7 x 10 19

sulfur- 1 x 1019

aluminum-2 x 1019

carbon-12.011u

sulfur-32.065u

aluminum-26.982u

6.02 x 1023

602,000,000,000,000,000,000,000

32.065u

26.982u

32.06

26.982

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