Using Moles to Count Atoms. Because chemists often deal with large numbers of small particles, they...
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Transcript of Using Moles to Count Atoms. Because chemists often deal with large numbers of small particles, they...
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= _______ )