Using Moles to Count Atoms

• Because chemists often deal with large numbers of small particles, they use a large counting unit—the abbreviated mol.

Mole -the SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in 12 g of carbon-12

(video 1)

• A mole is a collection of a very large number of particles

• About 602 213 670 000 000 000 000 000!

• This number is usually written as 6.022x1023/mol and is referred to as AVOGADRO’S CONSTANT

• The constant is named in honor of the Italian scientist Amedeo Avogadro. Avogadro’s constant is defined as the number of particles, 6.022 x1023, in exactly 1 mol of a pure substance.

• One mole of gumballs is 6.022 x1023 gumballs.

• One mole of popcorn is 6.022 x1023 kernels of popcorn

• Avogadro’s constant equals 6.022 1023/mol; the number of particles in 1 mol

(video 2)• You might wonder why 6.022 1023 represents

the number of particles in 1 mol. • The mole has been defined as the number of

atoms in 12.00 grams of carbon-12. • Experiments have shown that 6.022 x1023 is the

number of carbon-12 atoms in 12.00 g of carbon-12.

• One mole of carbon consists of 6.022 x1023 carbon atoms, with an average atomic mass of 12.01 amu.

• An ATOMIC MASS UNIT (AMU)- is unit of mass that describes the mass of an atom or molecule, is equal to one twelfth of the mass of carbon-12 atom (C12)

• Moles and grams are related. The mass in grams of 1 mol of a substance is called its MOLAR MASS

• molar mass the mass in grams of 1 mol of a substance

(video 4)

• Because the amount of a substance and its mass are related, it is often useful to convert moles to grams, and vice versa. You can use conversion factors to relate units.

(video 5)

• Ex: The shopkeeper knows that exactly 10 gumballs have a combined mass of 21.4 g. This relationship can be written as two equivalent conversion factors, both of which are shown below

10 gumballs/21.4g

21.4g/ 10 gumballs

• There is a relationship between the amount of an element in moles and its mass in grams.

• This relationship is graphed for iron nails Because the amount of iron and the mass of iron are directly related, the graph is a straight line.

• Ex: Determine the mass in grams of 5.50 mol of iron. ( molar mass of Fe = 55.85 g/mol Fe)

• Ex: What is the mass in grams of 2.50 mol of sulfur, S ( molar mass of S= ________ )

• Ex: Determine the amount of iron present in 352g of iron. (molar mass of iron= _______ )