Unit 2: Structure of Matter
Content Outline: Atomic Mass and the Mole Concept (2.3)
I. Mole (mol OR n)
A. This is a SI (Le Système International d’ Unités) unit (remember from Unit 1) that is used to represent the amount of a substance.
B. It can be written to show the number of atoms or molecules in a working sample of some element, compound, or molecule, such as sucrose (table sugar) – C6H12O6
1. This concept is very important because scientists, teachers and students cannot work with individual atoms or molecules because they are very, very small and can’t be handled one at a time.
2. So the mole was conceived to represent a working amount of a substance.
C. How to calculate a mole:
1. Determine the total atomic or molecular mass of the substance you are working with, using the chemical formula and Periodic Table. (Remember, how to find the Atomic Mass? – Hint…subscript.)
2. Then weigh out, using an electronic balance and weigh boat, that calculated amount.
3. Congratulations, you have just weighed out 1 mole of that substance!
For example: Atomic Mass
Aluminum has an atomic mass of 26.98 AMUs. So you would weigh out 26.98
grams of Aluminum to get a workable amount called a mole.
Molecular Mass
Salt (NaCl) has an atomic mass of: Sodium – 23.00 AMUs
Chlorine – 35.5 AMUs
Total AMUs = 23.00 + 35.5 = 58.5 AMUs Weigh out 58.5 grams of salt
The unit for of measurement is g/mol.
D. Molarity
1. Take your 1 mole of a substance and dissolve it in a small amount of distilled water, if it will dissolve, inside a volumetric flask. Then add distilled water to bring the volume to 1 L of distilled water. You now have a 1 Molar (1 M) solution.
2. Molarity is used for liquid solutions.
E. Amedeo Avogrado (1811)
1. He was an Italian physicist.
2. He proposed that the volume of a gas (at a given temperature & pressure) is proportional to the number of atoms, regardless of the type of gaseous substance used.
a. This eventually was modified to state: That in 1 mole of a substance there will always be 6.022 x 1023 atoms or molecules present. (That is a massive amount!)
b. This number became known as Avogrado’s constant when the French physicist Jean Perrin confirmed and proposed this in 1909 in honor of Avogrado’s work.
i. Jean Perrin would win the Nobel Prize for his work in 1926.
ii. The Nobel Prize is Sciences’ highest Award, The Super Bowl trophy in Pro Football.
c. Perhaps your class will celebrate Mole Day on October (10th month) 23 at 6:02 am.
II. Basic Measurements or Unit Conversions involving the Mole concept:
A. More than a mole: the basic concept is: amount you have/ amount of a mole = # of moles
You have 21.6 grams of Boron (B). How many moles do you have?
1 mole of Boron = 10.8 grams so… 21.6/10.8 = 2.0 moles.
You have 77.25 grams of Phosphorus (P). How many moles do you have?
1 mole of Phosphorus = 30.9 grams so… 77.25/30.9 = 2.5 moles.
B. Less than a mole: the basic concept is: amount you have/ amount of a mole = # of moles
You have 16.03 grams of Sulfur (S). How many moles do you have?
1 mole of Sulfur = 32.06 grams so… 16.03/32.06 = 0.5 moles
You have 2.43 grams of Magnesium (Mg). How many moles do you have?
1 mole of Magnesium = 24.30 grams so… 2.43/24.30 = 0.1 moles
C. Conversions from one unit to another unit involving the mole concept:
The basic concept is: Unit given x unit wanted = Unit wanted
unit given
The given unit cancels out and leaves you with the unit wanted.
1. Moles à Atoms/Molecules
a. You have 2.0 moles of Copper. How many atoms of Copper do you have?
1 mole = 6.022 x 1023 atoms so: 2 moles x 6.022 x 1023 atoms = 12.044 x 1023 atoms
1 mole
But using your rules for scientific notation, it becomes 1.2044 x 1024 atoms
b. You have 0.25 moles of Oxygen. How many atoms of Oxygen do you have?
1 mole = 6.022 x 1023 atoms so: 0.25 moles x 6.022 x 1023 atoms = 1.505 x 1023 atoms
1 mole
2. Atoms/Molecules à moles
a. You have 1.806 x 1024 atoms of Zinc (Zn). How many moles of Zinc do you have?
Step 1: Convert 1.806 x 1024 to 18.06 x 1023 (It must have the Avogrado exponent of 23.)
Step 2: 18.06 x 1023 Atoms x 1 mole = 3 moles
6.022 x 1023 atoms
b. You have 5.9 x 1022 atoms of Titanium (Ti) How many moles of Titanium do you have?
Step 1: Convert 5.9 x 1022 to 0.59 x 1023 (It must have the Avogrado exponent of 23.)
Step 2: 0.59 x 1023 Atoms x 1 mole = 0.098 moles
6.022 x 1023 atoms
3. Grams à Moles
a. You have 54.0 grams of Carbon (C). How many moles of Carbon do you have?
54.0 grams x 1 mole = 4.5 moles
12.0 grams
b. You have 10.0 grams of Nickel (Ni). How many moles of Nickel do you have?
10.0 grams x 1 mole = 0.17 moles
58.69 grams
4. Moles à Grams
a. You have 8.5 moles of Fluorine (F) gas. How grams of Fluorine do you have?
8.5 moles x 19.00 grams = 161.5 grams
1 mole
b. You have 0.45 moles of Scandium (Sc) gas. How grams of Scandium do you have?
0.45 moles x 44.96 grams = 20.23 grams
1 mole