Lesson 13 The Mole
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What Is a Mole?
Avogadro’s constant (the concept of the mole) is a scaling factor between microscopic amounts of chemicals and macroscopic amounts of chemicals.
B13.2 Mass of powder being weighed
A mole is a unit of measurement used in chemistry. In January 2018, IUPAC updated the definition of the mole. A mole now represents a number of particles—6.02 x 1023 particles to be precise.
1 mole = 6.02 x 1023 particles.
It is a similar concept to one dozen. If you have one dozen, you have 12 items. “Dozen” is a word that represents “counting.”
The mole is also a word that represents “counting” an exact number—just a really big number!
Atoms and molecules are incredibly small, and it would be almost impossible to carry out reactions at the molecular level. Avogadro’s constant (the concept of the mole) is a scaling factor between microscopic amounts and macroscopic amounts. For example, using the following chemical reaction,
2C(s) + O2(g) → 2CO(g)
you can interpret this reaction to mean 2 atoms of carbon react with 1 molecule of oxygen to produce 2 molecules of carbon monoxide. It would not be practical to work with such small amounts in the laboratory. Instead, the quantity is scaled up using the mole concept. This reaction can also be interpreted as 2 moles of carbon atoms react with 1 mole of oxygen molecules to produce 2 moles of carbon monoxide.
1 mole = 6.02 x 1023 particles.
It is a similar concept to one dozen. If you have one dozen, you have 12 items. “Dozen” is a word that represents “counting.”
The mole is also a word that represents “counting” an exact number—just a really big number!
Atoms and molecules are incredibly small, and it would be almost impossible to carry out reactions at the molecular level. Avogadro’s constant (the concept of the mole) is a scaling factor between microscopic amounts and macroscopic amounts. For example, using the following chemical reaction,
2C(s) + O2(g) → 2CO(g)
you can interpret this reaction to mean 2 atoms of carbon react with 1 molecule of oxygen to produce 2 molecules of carbon monoxide. It would not be practical to work with such small amounts in the laboratory. Instead, the quantity is scaled up using the mole concept. This reaction can also be interpreted as 2 moles of carbon atoms react with 1 mole of oxygen molecules to produce 2 moles of carbon monoxide.
Did You Know?
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B13.3 Amedeo Avogadro
B13.3 Amedeo Avogadro
Although Avogadro’s number is named after the Italian scientist Amedeo Avogadro, he is not the person who proposed the concept of the mole; it was just named in honour of him.
The concept of the mole is a method of counting and is different than the concept of mass of a sample. For example, if you were told you had 1 dozen feathers and 1 dozen elephants, you would know the following:
1 dozen feathers = 12 feathers
1 dozen elephants = 12 elephants
Would 1 dozen feathers weigh the same as 1 dozen elephants? The obvious answer is no; even though you have the same number, each individual entity has a different mass.
This is true for elements as well. One hydrogen atom would not weigh the same as one argon atom or the same as one copper atom.
B13.4 Modified Bohr diagram of hydrogen
B13.5 Modified Bohr diagram of argon
B13.6 Modified Bohr diagram of copper
This is because they are each composed of a different number of subatomic particles.
It then logically follows that one mole of each of these substances would also have different masses. The mass of one mole of an element is known as its molar mass and is located on the periodic table.
Mass of 1 mole of hydrogen = 6.02 Ă— 1023 particles = 1.01 g. (Or, the molar mass of hydrogen is 1.01 g/mol.)
Mass of 1 mole of argon = 6.02 Ă— 1023 particles= 39.95 g. (Or, the molar mass of argon is 39.95 g/mol.)
Mass of 1 mole of copper = 6.02 Ă— 1023 particles= 63.55 g (Or, the molar mass of copper is 63.55 g/mol)
Read This
Please read pages 107 and 108 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the definition of a mole. Remember,
if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice question to check your understanding of the concept you just learned. Make sure you write a complete answer to the practice
question in your notes. After you have checked your answer, make corrections to your response (where necessary) to study from.- Why is the concept of the mole needed?
The concept of the mole is needed as a way to scale between microscopic amounts and macroscopic amounts of chemical substances. - If you had 1 mole of sodium atoms, how many sodium atoms would you have?
6.02 x 1023 atoms. - If you had 1 mole of zinc atoms, how many zinc atoms would you have?
6.02 x 1023 atoms - If you had 1 mole of sodium atoms and 1 mole of zinc atoms, would the two samples have the same mass? Explain.
No, even though you have the same number of atoms, each individual atom does not have the same mass and the moles will not have the same mass either. - If you had 2 moles of sodium atoms, how many sodium atoms would you have?
2 Ă— (6.02 x 1023 particles) = 1.20 Ă— 1024 particles.