General Chemistry 1
Study Material and Lecture Notes: July 2018
Lesson 8: The Mole Concept and Molar Mass
The Mole
What is a mole? What is Avogadro’s number?
A special unit of measure, called the mole, is used to deal with extremely large
numbers. In the SI system, the mole is the amount of substance that contains as many
entities as there are in exactly 12 g of C-12. The number of atoms in 12 g of C-12 is
experimentally determined to be 6.022 x 1023. This is called Avogadro’s number.
Illustration of the mole with different counting units:
a. 1 dozen = 12 entities or units
b. 1 dozen eggs = 12 eggs
c. 1 dozen papayas = 12 papayas
d. 1 dozen cars = 12 cars
e. 1 dozen books = 12 books
f. 1 pair = 2 entities
g. 1 gross = 12 dozens = 144 entities
h. 1 ream = 500 entities
i. 1 mole = 6.022 x 1023 entities = 6.022 x 1023 of anything
Notes:
Mole Day is observed by chemists every October 23, from 6:02 am to 6:02 pm.
Misconception: Avogadro’s number is not a defined value. It is an experimentally
determined value. Mass spectroscopy techniques are used to determine the value
of Avogadro’s number to a high degree of accuracy.
While a dozen always has 12 entities, one dozen eggs will not have the same mass
as one dozen books, or one dozen oranges, or one dozen cars.
Practice Exercises 1
Answer the following:
1. How many eggs are there in one mole of eggs?
2. How many mongo beans are there in one mole of mongo beans?
3. How many sodium atoms are there in 1 mole of Na atoms?
4. Calculate the number of atoms of argon in 0.500 moles Ar?
, 5. How many moles of Co are there in 4.960 x 1025 atoms of Co?
6. How many molecules of H2O are there in 1 mole of water molecules?
7. How many molecules of carbon dioxide, CO2, are there in 2.648 moles CO2?
8. How many atoms of oxygen are there in 2.648 moles CO2?
9. Determine the number of moles of ammonia, NH3, in 8.254 x 1025 molecules of
ammonia.
ANSWER KEYS:
1. 6.022 x 1023 eggs
2. 6.022 x 1023 mongo beans
3. 6.022 x 1023 Na atoms
4. Solution:
5. Solution:
6. 6.022 x 1023 H2O molecules
7. Solution:
8. Solution:
Answer
9. Solution:
Answer
Molar Mass
Recall: The mole is the amount of substance that contains Avogadro’s number of units
or entities. But how much will one mole of a substance weigh?
The molar mass is the mass in grams of one mole of a substance.
One mole of C-12 has a mass of exactly 12 g and contains 6.022 x 1023 C-12 atoms. This
mass of C-12 is called the molar mass.
Study Material and Lecture Notes: July 2018
Lesson 8: The Mole Concept and Molar Mass
The Mole
What is a mole? What is Avogadro’s number?
A special unit of measure, called the mole, is used to deal with extremely large
numbers. In the SI system, the mole is the amount of substance that contains as many
entities as there are in exactly 12 g of C-12. The number of atoms in 12 g of C-12 is
experimentally determined to be 6.022 x 1023. This is called Avogadro’s number.
Illustration of the mole with different counting units:
a. 1 dozen = 12 entities or units
b. 1 dozen eggs = 12 eggs
c. 1 dozen papayas = 12 papayas
d. 1 dozen cars = 12 cars
e. 1 dozen books = 12 books
f. 1 pair = 2 entities
g. 1 gross = 12 dozens = 144 entities
h. 1 ream = 500 entities
i. 1 mole = 6.022 x 1023 entities = 6.022 x 1023 of anything
Notes:
Mole Day is observed by chemists every October 23, from 6:02 am to 6:02 pm.
Misconception: Avogadro’s number is not a defined value. It is an experimentally
determined value. Mass spectroscopy techniques are used to determine the value
of Avogadro’s number to a high degree of accuracy.
While a dozen always has 12 entities, one dozen eggs will not have the same mass
as one dozen books, or one dozen oranges, or one dozen cars.
Practice Exercises 1
Answer the following:
1. How many eggs are there in one mole of eggs?
2. How many mongo beans are there in one mole of mongo beans?
3. How many sodium atoms are there in 1 mole of Na atoms?
4. Calculate the number of atoms of argon in 0.500 moles Ar?
, 5. How many moles of Co are there in 4.960 x 1025 atoms of Co?
6. How many molecules of H2O are there in 1 mole of water molecules?
7. How many molecules of carbon dioxide, CO2, are there in 2.648 moles CO2?
8. How many atoms of oxygen are there in 2.648 moles CO2?
9. Determine the number of moles of ammonia, NH3, in 8.254 x 1025 molecules of
ammonia.
ANSWER KEYS:
1. 6.022 x 1023 eggs
2. 6.022 x 1023 mongo beans
3. 6.022 x 1023 Na atoms
4. Solution:
5. Solution:
6. 6.022 x 1023 H2O molecules
7. Solution:
8. Solution:
Answer
9. Solution:
Answer
Molar Mass
Recall: The mole is the amount of substance that contains Avogadro’s number of units
or entities. But how much will one mole of a substance weigh?
The molar mass is the mass in grams of one mole of a substance.
One mole of C-12 has a mass of exactly 12 g and contains 6.022 x 1023 C-12 atoms. This
mass of C-12 is called the molar mass.
