10-1: THE MOLE10-1: THE MOLE

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The MoleThe Mole

1. Avogadro’s Number 1. Avogadro’s Number (aka the MOLE):(aka the MOLE):A MOLE of somethingA MOLE of something (cars, bananas, atoms, (cars, bananas, atoms, molecules, people)molecules, people) is 6.02 x 10is 6.02 x 102323

This concept is similar to the idea of a “dozen”This concept is similar to the idea of a “dozen” being equal to 12 things (eggs, cookies, etc)being equal to 12 things (eggs, cookies, etc)Because atoms are so small, it takes a huge number of Because atoms are so small, it takes a huge number of them to make up a visible amount. them to make up a visible amount. The mole allows The mole allows us to talk about the number of atoms in a sample us to talk about the number of atoms in a sample we havewe have..

2. Where did chemists come 2. Where did chemists come up with that random number?up with that random number?

Named after the man who founded it Named after the man who founded it (Avogadro)(Avogadro)

In carbon-12 In carbon-12 (i.e. C with 6 protons and 6 (i.e. C with 6 protons and 6 neutrons, which has an atomic mass of neutrons, which has an atomic mass of 12 amu),12 amu), there are 6.02 x 10 there are 6.02 x 102323 C atoms in C atoms in 12 grams.12 grams.

Said another way, one mole of C atoms is Said another way, one mole of C atoms is 12 grams12 grams

The mole allowed chemists to talk about The mole allowed chemists to talk about how much of an element they have in how much of an element they have in gramsgrams

3. How big is Avogadro’s the 3. How big is Avogadro’s the number? Why is it so big?number? Why is it so big?

If you stacked a mole of sheets of If you stacked a mole of sheets of paper on top of each other, the stack paper on top of each other, the stack would reach beyond the solar systemwould reach beyond the solar system

This number is so large so we can This number is so large so we can reasonably talk about a HUGE amount reasonably talk about a HUGE amount of really tiny atomsof really tiny atoms

Working with the mole…Working with the mole…

First, let’s look at something familiar…First, let’s look at something familiar…4. Let’s say I have a dozen bikes. How many 4. Let’s say I have a dozen bikes. How many

wheels do I have? How many dozen wheels wheels do I have? How many dozen wheels do I have?do I have?

5. Let’s say I have one mole of bikes. How 5. Let’s say I have one mole of bikes. How many moles of wheels do I have?many moles of wheels do I have?

6.How many wheels do I have in 1 mole of 6.How many wheels do I have in 1 mole of bikes?bikes?

ANSWERSANSWERS

First, let’s look at something familiar…First, let’s look at something familiar…4. Let’s say I have a dozen bikes. How many 4. Let’s say I have a dozen bikes. How many

wheels do I have? How many dozen wheels wheels do I have? How many dozen wheels do I have?do I have?

2 dozen wheels or 24 wheels2 dozen wheels or 24 wheels5. Let’s say I have one mole of bikes. How 5. Let’s say I have one mole of bikes. How

many moles of wheels do I have?many moles of wheels do I have?2 moles of wheels2 moles of wheels

6.How many wheels do I have in 1 mole of 6.How many wheels do I have in 1 mole of bikes?bikes?2 moles wheels x 2 moles wheels x (6.02 x 10(6.02 x 102323)) = 1.2 x 10 = 1.2 x 1024 24

1 mole1 mole

Now let’s talk about Now let’s talk about atoms…atoms…

A: How many atoms/ions are in A: How many atoms/ions are in a compound?a compound?Look at the subscripts and add the total Look at the subscripts and add the total number of elements together. If necessary, number of elements together. If necessary, multiply by the total # of ions/elements. multiply by the total # of ions/elements.

Example: How many ions are there in the Example: How many ions are there in the compound CaClcompound CaCl22? ?

How many Cl ions are in the compound?How many Cl ions are in the compound?

If I have 12 CaClIf I have 12 CaCl22 compounds, how many Cl ions compounds, how many Cl ions do I have?do I have?

Example: How many ions are there in the compound CaClExample: How many ions are there in the compound CaCl22? ? Ca + Cl + Cl = 3Ca + Cl + Cl = 3

How many Cl ions are in the compound?How many Cl ions are in the compound?Cl + Cl = 2Cl + Cl = 2

If I have 12 CaClIf I have 12 CaCl22 compounds, how many Cl ions do I have? compounds, how many Cl ions do I have?

CaClCaCl2 2 CaClCaCl22 CaCl CaCl22 CaCl CaCl22 CaCl CaCl22 CaCl CaCl2 2 CaClCaCl2 2 CaClCaCl22 CaCl CaCl22 CaClCaCl22 CaCl CaCl22 CaCl CaCl22

OR OR 12 X 2 = 24 Cl atoms12 X 2 = 24 Cl atoms

B. How many moles of each B. How many moles of each type of atom/ion do I type of atom/ion do I

have?have? Multiply the number of moles by the Multiply the number of moles by the

subscript subscript Example: How many moles of Cl are in 5 Example: How many moles of Cl are in 5

moles of the compound CaClmoles of the compound CaCl22??

How many moles of Cl atoms are in How many moles of Cl atoms are in ONE mole?ONE mole?

Multiply by how many moles you have:Multiply by how many moles you have:

B. How many moles of each B. How many moles of each type of atom/ion do I have?type of atom/ion do I have?

Example: How many moles of Cl are in 5 Example: How many moles of Cl are in 5 moles of the compound CaClmoles of the compound CaCl22??

How many MOLES of Cl atoms are in How many MOLES of Cl atoms are in ONE mole?ONE mole?2 atoms per compound 2 atoms per compound 2 moles Cl 2 moles Cl per moleper mole

Multiply by how many moles you have:Multiply by how many moles you have:10 moles Cl10 moles Cl

C. How many atoms/ions do C. How many atoms/ions do I have?I have?

Multiply the number of MOLES of the atom by Multiply the number of MOLES of the atom by Avogadro’s number. Avogadro’s number.

Example: How many ions of Cl are in 5 moles of Example: How many ions of Cl are in 5 moles of compound CaClcompound CaCl22??

First find the total # of moles of Cl:First find the total # of moles of Cl:

Use Avogadro’s number as a conversion Use Avogadro’s number as a conversion factor:factor:6.02 x 106.02 x 102323

1 mole (cancel units you don’t 1 mole (cancel units you don’t want)want)

C. How many atoms/ions do C. How many atoms/ions do I have?I have?

Multiply the number of MOLES of the atom by Multiply the number of MOLES of the atom by Avogadro’s number. Avogadro’s number.

Example: How many ions of Cl are in 5 moles of Example: How many ions of Cl are in 5 moles of compound CaClcompound CaCl22??

First find the total # of moles of Cl:First find the total # of moles of Cl:10 moles Cl10 moles Cl

Use Avogadro’s number as a conversion factor:Use Avogadro’s number as a conversion factor:6.02 x 106.02 x 102323

1 mole (cancel units you don’t want)1 mole (cancel units you don’t want)

10 moles Cl x10 moles Cl x 6.02 x 106.02 x 102323 = 6.02 x 10 = 6.02 x 102424 Cl atoms Cl atoms 1 mole 1 mole