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**Using Moles to Count Atoms**

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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)

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

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

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The constant is named in honor of the Italian scientist Amedeo Avogadro. Avogadro’s constant is defined as the number of particles, x1023, in exactly 1 mol of a pure substance. One mole of gumballs is x1023 gumballs. One mole of popcorn is x1023 kernels of popcorn

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**Avogadro’s constant equals 6**

Avogadro’s constant equals /mol; the number of particles in 1 mol (video 2) You might wonder why represents the number of particles in 1 mol. The mole has been defined as the number of atoms in grams of carbon-12. Experiments have shown that x1023 is the number of carbon-12 atoms in g of carbon-12.

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**One mole of carbon consists of 6**

One mole of carbon consists of x1023 carbon atoms, with an average atomic mass of 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

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**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)

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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

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**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.

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**Ex: Determine the mass in grams of 5. 50 mol of iron**

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

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**Ex: What is the mass in grams of 2**

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

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**Ex: Determine the amount of iron present in 352g of iron**

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

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